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Title: The rat and its relation to the public health
Author: Various
Release date: August 4, 2025 [eBook #76630]
Language: English
Original publication: Washington: Public Health and Marine Hospital Service of the United States, 1910
Credits: Richard Tonsing and the Online Distributed Proofreading Team at https://www.pgdp.net (This file was produced from images generously made available by The Internet Archive)
*** START OF THE PROJECT GUTENBERG EBOOK THE RAT AND ITS RELATION TO THE PUBLIC HEALTH ***
TREASURY DEPARTMENT
Public Health and Marine-Hospital Service of the United States
THE RAT AND ITS RELATION TO THE PUBLIC HEALTH
BY VARIOUS AUTHORS
PREPARED BY DIRECTION OF THE SURGEON-GENERAL
[Illustration: [Logo]]
WASHINGTON
GOVERNMENT PRINTING OFFICE
1910
TABLE OF CONTENTS.
Page.
_Introduction_ (Walter Wyman) 9
_Natural History of the Rat_ (David E. Lantz) 15
Classification of rats 15
Distribution of the genus _Mus_ in America 17
History of the brown rat 19
General description of the species in America and key to the
species 20
Habits of rats 22
Breeding habits 22
Abundance 23
Migrations and invasions 24
Food 26
Feeding habits 26
Ferocity 27
_Plague Infection in Rats_ (George W. McCoy) 29
Mode of examination 30
Gross lesions of natural rat plague, acute 32
Subcutaneous injection 32
The bubo 33
The granular liver 34
The spleen 35
Pleural effusion 35
Gross lesions of natural rat plague, chronic 36
Rat plague without gross lesions 37
Microscopical examinations 37
Bacteriological diagnosis of rat plague 38
Pest-like bacteria found in rats 41
Artificial infection of rats with plague 41
Modes of infection 42
Local reaction 43
The bubo 44
The liver and spleen 44
Chronic plague due to artificial inoculation 44
The histology of rat plague 45
Natural rat plague 46
Immunity of rats to plague 46
References 48
_Rat Leprosy_ (Walter R. Brinckerhoff) 49
Introduction 49
Review of literature 49
Description of disease 50
Etiology 52
Summary 52
Bibliography 53
_Bacterial Diseases of the Rat other than Plague_ (Donald H.
Currie) 55
Danysz bacillus or bacillus typhi Murium of Loeffler 55
Pneumonia 55
Staphylococcus abscesses 56
Bacillus pseudo-tuberculosis rodentium (Pfeiffer) 57
Toyama’s bacillus 57
Infections of mice 57
_Organic Diseases of the Rat, Including Tumors_ (George W. McCoy) 59
Usefulness of wild rats for laboratory purposes 59
Circulatory apparatus 60
Pulmonary apparatus 60
Digestive tract 61
Cirrhosis of the liver 61
Fatty degeneration of the liver 61
Hernia 61
Genito-urinary tract 62
Nephritis 62
Abscess of the kidney 62
Atrophy of the kidney 63
Vesical calculi 63
Tumors 64
Metastases 67
Histological structure 67
Lipomata 67
Fibromata 67
Sarcomata 67
Adenomata and Carcinomata 67
_Ectoparasites of the Rat_ (Nathan Banks) 69
Fleas—Siphonaptera 69
Lice—Anoplura 77
Mites—Acarina 80
_Internal Parasites of Rats and Mice in Their Relation to
Diseases of Man_ (Ch. Wardell Stiles and Charles G. Crane) 87
Summary 87
Introduction 87
Protozoa 88
Cestoda 95
Nematoda 101
Acanthocephala 108
_Compendium of Animal Parasites Reported for Rats and Mice—(Genus
Mus)_ (Ch. Wardell Stiles and Albert Hassall) 111
_The Flea and Its Relation to Plague_ (Carroll Fox) 123
Theories as to the transmission of plague 123
Insects that have been suspected in the transmission of plague 124
Experiments proving that fleas can transmit plague 125
The bacillus in the flea 126
How the flea clears itself of bacilli 127
Regional distribution of fleas on rats 127
Anatomy of the mouth parts of the Ceratophyllus Fasciatus 128
Outside the head 128
Inside the head 129
The act of biting 131
How the flea infects its host 132
Enumeration of fleas that have been found on rats 133
Results of identification of fleas in California 135
Synopsis of fleas commonly found on rats 136
Ceratophyllus Fasciatus, Bosc 136
Lœmopsylla Cheopis, Rothschild 138
Ctenopsyllus Musculi, Dugés 140
Pulex Irritans, Linnæus 142
Ctenocephalus Canis, Curtis 143
References 144
_Rodents in Relation to the Transmission of Bubonic Plague_
(Rupert Blue) 145
Epidemiological observations in San Francisco 147
Theories as to the cause of seasonal prevalence 149
The occurrence of plague in the marmot of Asia and ground
squirrel of California 150
Plague infection in ground squirrels 150
The natural habitat of plague 151
References 152
_Rodent Extermination_ (Wm. Colby Rucker) 153
Trapping 154
Poisoning 156
Natural enemies 159
Cutting off of the rat’s food supply 160
Building the rat out of existence 161
_Natural Enemies of the Rat_ (David E. Lantz) 163
Animals that destroy rats 163
Hawks 163
Owls 164
Wild mammals 166
Skunks 166
Weasels 166
Minks 167
Domestic animals 167
Dogs 167
Cats 167
Ferrets 168
Other animals 168
Mongoose 168
Alligators 168
Snakes 169
Bounties on predatory animals 169
_Rat-Proofing as an Antiplague Measure_ (Richard H. Creel) 171
Rat-proofing of primary importance 173
Rat-proofing is expensive 174
Methods of rat-proofing 175
Rat-proofing ordinances should be specific 177
Choice of architecture and building materials 178
_Inefficiency of Bacterial Viruses in the Extermination of Rats_
(Milton J. Rosenau) 179
Introduction 179
Experiments upon rat virus in the Hygienic Laboratory 183
Experiments with microorganisms for destroying rats by the U.
S. Biological Survey 186
Experiments during the San Francisco plague outbreak 188
Opinions of others 190
Pathogenicity for man 193
References to the literature 201
Résumé 204
_Plague Eradication in Cities by Sectional Extermination of Rats
and General Rat-Proofing_ (Victor G. Heiser) 205
_The Rat in Relation to Shipping_ (Wm. C. Hobdy) 207
Adaptability of the rat to his surroundings 208
Damage to cargo 209
Fumigation 211
Summary 213
_The Rat as an Economic Factor_ (David E. Lantz) 215
Introduction 215
Utility of the rat 215
Destructiveness of the rat 216
Grains 216
Merchandise in stores and warehouses 218
Merchandise in transit 219
Poultry and eggs 219
Game and wild birds 220
Fruit and vegetables 221
Flowers and bulbs 221
Fires 222
Buildings and furniture 222
Miscellaneous 223
Amount of losses caused by rats 224
Indirect losses 225
_The Rat in Relation to International Sanitation_ (John W. Kerr) 227
International sanitary regulations 228
Inquiry into the crusade against rats throughout the world 230
Rat extermination in United States ports 231
Rat extermination in Chinese cities 232
Rat extermination in Madras, Bombay, and Calcutta, India 234
Rat extermination in Yokohama and Nagasaki, Japan 235
Rat extermination in East Africa 237
Rat extermination in Cape Town, South Africa 238
Rat extermination in Alexandria and Cairo, Egypt 238
Extermination of rats at the port of Constantinople 238
Rat extermination in Russian ports 239
Destruction of rats in Trieste, Austria 240
Destruction of rats in Genoa, Italy 240
Destruction of rats in Barcelona, Spain 241
Rat destruction in French ports 241
Ministerial decree relating thereto 242
Destruction of rats in German ports 243
Measures against rats in Rotterdam, Holland 245
Destruction of rats at Antwerp, Belgium 245
Destruction of rats in Denmark 245
Danish law of March 22, 1907 245
Collection and destruction 247
Destruction of rats in Swedish ports 248
Destruction of rats in English ports 249
Measures against rats in Australian ports 250
Measures against rats in South American ports 252
Measures against rats in West Indian ports 252
Destruction of rats in Panama 253
Measures against rats in Vancouver, B. C. 253
Necessity of concerted action of nations 254
LIST OF ILLUSTRATIONS.
Page.
Fig. 1a. Upper molars of the brown rat (_Mus_): tubercles in 16
three rows
Fig. 1b. Upper molars of the rice rat (_Oryzomys_): tubercles in 16
two rows
Fig. 2a. Right hind foot of brown rat, showing long sixth foot 17
pad
Fig. 2b. Right hind foot of house mouse, showing round sixth 17
foot pad
Fig. 3a. Ears of brown rat and black rat, showing relative size 21
fig. 3b.
Fig. 4. Necropsy appearance of normal rat 48
Fig. 5. Necropsy appearance of plague-infected rat 48
Fig. 6. Flea, showing the various parts 70
Fig. 7. Louse—_Polyplax spinulosus_ 78
Fig. 8. Mite—_Lælaps echidninus_ 81
Figs. 9 Internal parasites of rats and mice 90–109
to 58.
Fig. 59. Isolated plague-infected center, Manila, P. I. 206
Fig. 60. Scheme for testing rat-plague infection, Manila, P. I. 206
Plate I. Mouth parts of _Ceratophyllus fasciatus_ 130
II. _Ceratophyllus fasciatus_ 136
III. _Lœmopsylla cheopis_, Rothschild 138
IV. _Ctenopsyllus musculi_, Duges 140
V. _Pulex irritans_, Linnæus 142
VI. _Ctenocephalus canis_, Curtis 144
THE RAT AND ITS RELATION TO THE PUBLIC HEALTH.
By WALTER WYMAN,
_Surgeon-General of the Public Health and Marine-Hospital Service_.
INTRODUCTION.
The science of bacteriology has elucidated many facts with respect to
the causation of disease, and with this advance in knowledge, old
theories regarding the miasmatic and humoral origin of human ills have
been abandoned.
Epidemiological studies have likewise determined the methods of
transmission of many of the infectious and contagious diseases, thus
eliminating erroneous conceptions that they are attributable to some
mysterious condition of the atmosphere or soil, or to a visitation of
the wrath of the Almighty.
Both these sciences have contributed to our knowledge of the
relationship of living things, particularly with respect to their
influence upon each other in relation to health and disease. It is now
known, for instance, that mosquitoes are the pests of man, not only
because of their bites, but because they at times transmit malaria,
dengue, filariasis, and yellow fever. So, too, it is known that rodents
are the enemies of man, not only because of the toll exacted from him,
but because they are the principal agents in the propagation and spread
of bubonic plague.
Ancient writings abound in allusions to pestilences and their connection
with epizootics among rats and mice.
In the Book of Samuel there is reference to a pestilence having relation
to mice, and that it might be stayed the Philistines made offerings of
golden images of the mice that marred the land.
During the centuries that have intervened rats have migrated to
practically every quarter of the earth, causing untold losses on account
of their depredations. They have also, in all probability, been the
primary agents of transmission in the pandemics of plague which have
visited the earth. The fact that plague is due to a specific
microorganism, and that its presence in man is also associated with
epizootics in rats, has led to a more careful study of this animal,
particularly in relation to his habits, the diseases from which he
suffers, and the methods necessary to his control. Prior to the
beginning of the present pandemic of plague which had its origin in
China, interest in the rat was almost wholly an economic and financial
one. Since that time evidence has been rapidly accumulating which proves
that this animal and his parasites are responsible for the transmission
of plague and that plague itself is essentially a disease of the rat.
A knowledge of this animal on the part of the sanitarian therefore
becomes essential. During the enforcement of antiplague measures in
California, Hawaii, the Philippine Islands and elsewhere, observations
of great value have been made and their practical application has
resulted in better directed efforts for the elimination of the disease.
In studies of plague and leprosy with the view to their diagnosis and
control, it is not enough now to isolate the microorganisms responsible
for these diseases, but the sanitarian must be able to recognize the
pathological conditions present in animals affected, and to do so he
must have practical knowledge of this subject in order that he may
differentiate between the various diseases from which these animals
suffer.
Opportunity for observation and study of the diseases of rats and the
methods necessary to their eradication has been afforded to the officers
of the Public Health and Marine-Hospital Service who are constantly
stationed on the outposts in the warfare against exotic diseases. The
results of these observations have been utilized by officers of the
service, and some of them have been published for the benefit of others.
The rat has received much attention of late in other parts of the world.
In Denmark, for instance, a legalized warfare against rodents has been
begun, principally on account of their influence in the transmission of
trichinosis. In England there exists The Incorporated Society for the
Destruction of Vermin, and in other places rat destruction is being
agitated both from economic and public health standpoints.
In view of the great importance of the rat in relation to the public
health, it has been thought advisable to collect and publish all
pertinent information on the subject, in order that public health
officials who should be on the lookout for the appearance of plague
among rodents might have available a reliable treatise on the subject.
Studies of rodents from a biologic and economic standpoint come within
the province of other departments of the public service, and the
cooperation of the Biological Survey and Bureau of Entomology of the
Department of Agriculture was therefore requested and received.
The subjects dealt with in this publication have been prepared by those
having wide experience.
In the chapter on natural history by Mr. David E. Lantz there is given a
classification of rats as well as the distribution of the genus _Mus_ in
America. An interesting and important fact is mentioned that the
Biological Survey has no records of the presence of the brown rat in
Nevada, Utah, Wyoming, Idaho, and the greater part of Montana. Mr. Lantz
also describes the different species in America, and refers to their
habits as to breeding, feeding, migrations, invasions, and ferocity. The
facts presented by him emphasize the great difficulty of ridding cities
of these pests.
Passed Assistant Surgeon McCoy discusses plague infections in rats and
describes the methods of examination. He also describes the gross
lesions found in plague rats, gives the bacteriologic diagnosis of rat
plague and the cultural characteristics of the plague bacillus on
various media. He gives the methods of artificial infection of rats with
plague, and reviews the recent work of Ledingham in relation to the
histology of rat plague. Finally, he presents results of his own
investigations to show that the wild rat is not especially susceptible
to plague infection, and that a certain percentage of such animals enjoy
a natural immunity to plague.
Doctor Brinckerhoff discusses rat leprosy; states that it is very
similar to human leprosy, and that it is caused by a bacillus which
closely resembles the bacillus of Hansen. He describes the pathological
changes found, and expresses the hope that the disease will receive
further earnest study, in order that additional information may throw
light on the problems presented by leprosy in man.
Passed Assistant Surgeon Currie briefly outlines the bacterial diseases
of the rat, other than plague and leprosy. He mentions the great utility
that would follow the discovery of a rat destroying bacterium, but
states that it appears now more than probable that few such natural
diseases of rats exist.
In a chapter on organic diseases of the rat, Doctor McCoy summarizes the
results of his observations made during examinations of these animals in
the Federal laboratory of the service at San Francisco. These
observations are of interest, and will assist those engaged in such work
to further classify the pathological changes noted as well as
differentiate them from plague.
The ectoparasites of the rat are classified and described by Mr. Nathan
Banks, and he has presented in condensed form information of much
practical value upon the subject.
Dr. Ch. Wardell Stiles discusses the internal parasites of rats and mice
in relation to the diseases of man. He regards the rat as a permanent
reservoir for trichinosis, and states that this disease will probably
never be eradicated from man until rats and mice are practically
eradicated, and a national campaign directed against trichinosis must
take the rat into consideration.
A compendium of animal parasites reported for rats and mice is presented
in a chapter by Ch. Wardell Stiles and Albert Hassall. While, as the
authors state, no list of this kind can ever lay claim to being
complete, it represents the present knowledge of the subject.
In a discussion of the flea and its relation to plague, Passed Assistant
Surgeon Fox summarizes the theories as to the transmission of this
disease. He also mentions the insects that have been suspected of
transmitting plague and presents accumulated evidence that fleas
actually convey the infection. He then gives the anatomy of the mouth
parts of the _Ceratophyllus Fasciatus_, the common rat flea of North
America. He also enumerates the fleas that have been found on rats, and
gives the results of identifications of 19,768 fleas in San Francisco
and Oakland, Cal. The plates accompanying this article, and their
description should be of great value to those engaged in antiplague
measures.
Surgeon Blue briefly discusses the subject of rodents in relation to the
transmission of bubonic plague. He discusses the theories as to the
cause of seasonal prevalence of this disease and presents a table
showing the number of rats examined during the different months of the
year, the number found infected, the average temperature and rainfall
for those months and the character of the days, as to the number clear,
partly cloudy, or cloudy. He refers to plague infection in ground
squirrels in California and warns against the possibility that this
animal may become responsible for the establishment of a permanent focus
of plague on the Pacific coast of the United States, as the marmots are
so concerned with regard to India.
The all-important subject of rodent extermination is considered in
detail, various phases of the subject being dealt with by different
authors.
Passed Assistant Surgeon Rucker discusses the destruction of these
animals by trapping, poisoning, cutting off of food supply, and
destroying of existing nests and at the same time preventing the making
of new ones. He describes the methods of use of the various mineral
poisons, but finally states that rodents must be builded out of
existence; in other words, habitations must be rendered rat proof.
Mr. Lantz, in discussing the natural enemies of the rat, mentions the
animals that destroy these pests. He concludes that on account of this
function bounties for the destruction of small animals that prey on
rodents can not be justified and that they should in the future be
protected in every way possible.
Passed Assistant Surgeon Creel discusses rat proofing as an antiplague
measure, and gives in detail the principles of construction necessary.
He concludes that rat proofing is the most valuable antiplague measure,
and that it should precede auxiliary measures such as trapping and
placing of poisons.
Surgeon Rosenau discusses the bacterial viruses in relation to rat
destruction. As a result of his investigations in the hygienic
laboratory and the reports of investigations and practical use
elsewhere, he concludes that the bacterial viruses have signally failed
to accomplish the mission for which they were intended, and that they
are not entirely harmless to man, as has been stated.
Passed Assistant Surgeon Heiser briefly outlines the measures
recommended for the eradication of plague in cities by means of
sectional extermination of rats and general rat proofing. He gives
results following this method of procedure in Manila, and presents
charts showing how to deal with infected city districts.
Passed Assistant Surgeon Hobdy, in a chapter on the rat in relation to
shipping, refers to the voyage-making tendencies of the rodent, its
destructiveness aboard ship, and its power of adapting itself to unusual
conditions and surroundings. In one small lumber vessel fumigated by
Doctor Hobdy at the Angel Island quarantine station there were collected
525 dead rats. Mention is also made of another vessel on which were
collected 1,700 rats after fumigation. He discusses the methods by which
it gains access to vessels, and outlines the practices that should be
observed to keep it off. He also describes in some detail the measures
to be adopted for its destruction after it has gotten aboard ship, and
mentions the different methods of fumigation.
Mr. Lantz, in a third paper, discusses the rat as an economic factor,
and states in his paper that they do not serve any useful purpose. On
the other hand, they cause enormous loss through damage to grain,
merchandise, poultry and eggs, game and wild birds, fruit and
vegetables, and flowers and bulbs. They also cause damage by setting
fire to buildings and destroying furniture. He refers to various
estimates made of the losses in the United States from rats, and they
vary from $35,000,000 to $50,000,000 a year; but at the same time he
states that, with present information, any attempt to state the amount
of loss from rats would be largely guesswork.
Assistant Surgeon-General Kerr refers to the rat as a factor in
international sanitation, and briefly outlines the provisions contained
in international sanitary agreements for their eradication. He reviews
the efforts being made at the more important seaports to exterminate
rats, as well as the methods being employed to that end. The information
presented is, in part, compiled from consular reports received through
the Department of State. There are given, so far as obtainable, copies
of laws and ordinances enacted for the destruction of rats and the
different methods practiced in ports where plague has prevailed, and the
facts presented indicate that a more or less widespread crusade against
rats is being carried on. He expresses the belief that it is too much to
expect that the rat population can ever be exterminated from any city,
but that it is not too much to expect that ocean carriers can be freed
from rodents and kept so, which action would confine plague within
continental boundaries.
Epidemiological studies made of plague since the adoption of the
International Sanitary Convention of Paris and the International
Sanitary Convention of Washington have proven that the rat and its
parasite, the flea, are the agents of transmission of the disease. In
other words, where rats go plague will go. I believe, therefore, that in
order to stop the further progress of plague, radical measures should be
adopted, and in a communication of February 26, 1909, addressed to the
Secretary of State, I suggested the advisability of submitting the
question of a systematic destruction of rodents aboard ship to an
international sanitary conference, with the view to the adoption of an
international sanitary regulation on the subject. The adoption of such a
regulation would undoubtedly lessen quarantine restrictions, prevent the
destruction of cargo by rodents, and obviate the danger of the further
spread of plague.
Until ships are freed from rats, each country must take all necessary
precautions, consistent with international agreements, to destroy rats;
and the sanitary authorities of infected localities must, at great
expense, determine the extent of infection among rodents, with the view
to its elimination. This problem when it presents itself in a community
is of great magnitude, and those responsible for its solution should be
familiar with all its phases.
It is with the view to supplying the necessary information in one
treatise that this publication is issued. In its preparation the bureau
has had the cooperation of the Department of Agriculture and
acknowledgements are due, and here made to, the officers of that
department for their hearty cooperation in contributing some of the
chapters which follow.
NATURAL HISTORY OF THE RAT.
By DAVID E. LANTZ.
_Assistant, U. S. Biological Survey, Department of Agriculture_.
INTRODUCTION.
The extermination of rats has become one of the serious problems of
modern times. That such noxious animals should have flourished so long
is not creditable to our civilization. While no kind of rat can be
regarded as harmless, the various species differ greatly in harmfulness.
In comparison with the cosmopolitan species that have reached our shores
from the Old World, our native rats do little damage. It is important,
therefore, to be able to recognize the introduced forms, to understand
their habits, and to concentrate efforts for their extirpation.
CLASSIFICATION OF RATS.
Rats and mice belong to the _Rodentia_, an order which comprises more
than a third of all living species of mammals. Also, it exceeds any
other mammalian order in the number of its individuals.
Rodents are mainly herbivorous mammals, mostly of small size, having a
furry, sometimes a spiny, integument, clawed digits, and usually
plantigrade feet. The most important distinguishing character of the
order is its dentition. This is marked by the absence of canine teeth
and the presence of strongly developed incisors growing from permanent
pulps. The incisors are never more than two in the lower jaw and usually
but two in the upper. They are elongated, curved, chisel-like in shape,
and continue to grow throughout the life of the animal. Only the front
of these teeth is covered with enamel, a provision which keeps them
sharp by the more rapid wearing away of the softer dentine in the body
of the tooth, as the upper and lower pairs meet in gnawing. Between the
incisors and the cheek, or molar, teeth of rodents there is a wide,
vacant space, marking the entire absence of canines.
The most extensive family of rodents is the _Muridæ_, a name which
applies to rats and mice in the widest sense of those terms. It is
difficult to characterize the family, since its members differ widely.
However, most of them are rat-like in form and light and active in
movements. None of the family have premolars; and, except in a single
genus (_Hydromys_), the number of molars is three. Oldfield Thomas, the
eminent English zoologist, includes in this family no less than 77
genera, or almost half the total of 159 which he ascribes to the whole
order _Rodentia_.[A] He further subdivides the _Muridæ_ into a dozen
subfamilies, of which the _Murinæ_ and the _Sigmodontinæ_ are the most
extensive. The name _Cricetinæ_ is now generally used instead of
_Sigmodontinæ_, though not always with the same limitations.
Footnote A:
Proc. Zool. Soc., pp. 1012–1028, 1896.
The _Murinæ_ comprise only Old World rats and mice, while the
_Cricetinæ_ are, in the main, American forms. In the _Murinæ_ the cusps,
or tubercles, of the unworn upper molars are arranged triserially, or in
three longitudinal rows; in the _Cricetinæ_ they are arranged
biserially, one row on the outer and one on the inner margin (fig. 1).
The wearing away of these cusps leaves characteristic curved lines of
hard enamel surrounding areas of dentine. When the cusps are in pairs
the worn pattern looks somewhat like the Greek letter sigma (Σ), whence
the name sigmodont, often applied to native American rats and mice.
[Illustration:
Fig. 1a. Fig. 1b.
FIG. 1a.—Upper molars of the brown rat (_Mus_): tubercles in three
rows.
FIG. 1b.—Upper molars of the rice rat (_Oryzomys_): tubercles in two
rows.
]
The _Murinæ_ are the true rats and mice, typified by the genus _Mus_,
which contains by far the largest number of species. Trouessart, in his
Catalogus Mammalium, enumerates 260 species of _Mus_ described before
1905. Since that date a number of new forms have been described.
The genus _Mus_ is characterized by narrow, ungrooved incisors; three
small, rooted molars; soft fur mixed with hairs, sometimes with spines;
a rudimentary pollex having a short nail instead of a claw; a long tail
bearing rings of overlapping scales and often naked or nearly so. The
ears are rather large, the eyes bright and prominent, and the muzzle
somewhat pointed. The members of the genus are natives of the Old World,
throughout which, with the exception of Madagascar, they are quite
generally distributed. Nearly seven-eighths of the whole number of
species are commonly called rats.
The distinction between rats and mice is arbitrary and based on size.
Exclusive of the tail, rats may be said to vary in length from 4½ to 10
inches or more, while mice measure from 2 to 4 inches. With few
exceptions, rats have six well-defined footpads (plantar tubercles), the
last on the hind foot being elongated in shape; the last hind-foot pad
of mice is usually circular (fig. 2).
Of the many species of _Mus_ only three or four have developed the
ability to adapt themselves to such a variety of conditions as to become
cosmopolitan. Four have found lodgment in America: The common house
mouse (_Mus musculus_); the old English black rat (_Mus rattus_); the
Egyptian, or roof, rat (_Mus alexandrinus_); and the brown rat (_Mus
norvegicus_), known also as the gray rat, barn rat, wharf rat, sewer
rat, and Norway rat. The black rat and the roof rat differ from each
other chiefly in color. Indeed some zoologists regard them as races of
the same species, and the trinomial _Mus rattus alexandrinus_ for the
roof rat is now in use among zoologists.
[Illustration:
FIG. 2a.—Right hind foot of brown rat, showing long sixth foot pad.
FIG. 2b.—Right hind foot of house mouse, showing round sixth foot pad.
]
DISTRIBUTION OF THE GENUS MUS IN AMERICA.
The common house mouse (_M. musculus_) found its way to America soon
after the first settlement by Europeans. It now inhabits all settled
parts of North and South America, as well as nearly the entire Old
World; but in very cold regions it does not always survive the winters,
and is therefore comparatively scarce or local. It almost always reaches
a new settlement sooner than the rat.
The black rat (_M. rattus_) has been known in Europe since the twelfth
century. It was carried to South and Middle America about three and a
half centuries ago (1554). The time of its arrival in the English
colonies of North America is not known with certainty, but it was well
established in the settled parts by the beginning of the eighteenth
century. Soon after the arrival of the brown rat, the black species
began to decrease in numbers, and has become extinct in most localities.
At present it is not uncommon in some parts of the South, and still
occurs in scattered colonies in Canada and some of the States east of
the Mississippi, and also on some of the coastal islands. It is
occasional in many of our seaports, being apparently brought from the
Far East in merchandise. Except in a few ports like San Francisco, where
new arrivals are probably rather frequent, these introduced individuals
are often destroyed before they multiply. The history of the black rat
in Europe and its disappearance before the brown rat is an exact
parallel to its history here, and the animal is now comparatively rare
north of the Alps, except in the Channel Islands.
The Biological Survey has specimens of the black rat from Massachusetts,
New Hampshire, Georgia, Florida, Alabama, California, and Washington,
and also from Mexico, Honduras, Nicaragua, and Hawaii. There are
authentic records of its recent occurrence in Newfoundland, Quebec, Nova
Scotia, New York, North Carolina, Tennessee, West Virginia, and
Mississippi. In parts of South and Middle America it is abundant.
The roof or Alexandrian rat (_M. alexandrinus_) is similar to the black
rat in form and general habits, though not in color. Little is known of
its history, but it is thought to be a native of Egypt, where it is
still abundant. It has established itself in many parts of the world,
mainly in warm climates, and is common near the coast in the southern
parts of the United States.
The Biological Survey has specimens of the roof rat from North Carolina,
Georgia, Florida, Alabama, Mississippi, Texas, Arizona, and California.
In the last-named State it is abundant in the Sacramento Valley. It is
known also from Dismal Swamp, Virginia, and from Cuba, the Bermudas,
Trinidad, San Domingo, Costa Rica, Nicaragua, Mexico, and Hawaii. Also,
it inhabits many parts of South America, where in places it is the
dominant species.
The most destructive of the rat family is the brown rat (_M.
norvegicus_). In most parts of the United States it is the common rat
about houses and barns in the country and about markets, wharves, and
warehouses in cities. It is larger and more robust than either the black
or the roof rat, and differs from both in habits. It is more of a
burrower, and lives in excavations which it makes under buildings and in
loose soil along hedges and river banks. This habit, combined with its
greater strength and ferocity has enabled it to supplant the other
species in temperate latitudes; but in the warmer parts of America and
the Old World it has not been able to drive out the others. The house
mouse everywhere holds its own against the brown rat by its ability to
escape into retreats too small for the rat to follow.
The brown rat inhabits most of the thickly populated parts of America.
North of Panama it occurs generally except in the arid interior, from
the Isthmus to the Yukon Valley and southern Greenland. In the Great
Basin it is practically unknown, and in New Mexico and Arizona it is
confined chiefly to towns along the railroads. The Biological Survey is
without records of its presence in Nevada, Utah, Wyoming, Idaho, and the
greater part of Montana. The reason for its absence in that region is
not understood, but its ability to withstand extreme cold is proved by
the fact that it flourished in latitude 78° 37′ north on board Doctor
Kane’s ship _Advance_, in the Second Grinnell Expedition, during the two
winters when that vessel was icebound. It has also adapted itself to the
continuous low temperatures of cold-storage warehouses, in which it
appears to breed freely.
HISTORY OF THE BROWN RAT.
We know little of the history of this species. Greek and Roman writers
make no mention of rats of any kind, but possibly knew the animals and
included them in their frequent references to mice. Pallas, in 1778,
described the brown rat under the name _Mus decumanus_, and this was
generally used until it was found that Erxleben had called it _M.
norvegicus_ in 1777. Previously, the common name Norway rat had often
been used for this species.
The brown rat is generally supposed to be of Asiatic origin. Various
modern writers have asserted that it came originally from Persia or
India; but W. T. Blanford states that the species is at present unknown
in Persia, and that in India the black rat is the generally distributed
species, while the brown rat occurs only along the coast and the
navigable rivers.[B] This implies that the latter species is a
comparatively recent immigrant into India.
Footnote B:
Fauna of British India. Mammals, p. 409, 1891.
As regards the arrival of the brown rat in Europe, two facts are known.
The species reached England from some eastern port about 1728 or 1729,
and according to Pallas, a little earlier, 1727, crossed the Russian
frontier from Asia and soon spread over the greater part of that
country.[C] This statement, taken in connection with that of Blanford,
makes it highly probable that before this migration the Asiatic home of
the species was north, rather than south, of the high mountains of
northern India. This view, which has been adopted by several
naturalists, is further strengthened by the fact that the animal
flourishes better in temperate than in tropical climates.
Footnote C:
Zoographica, Rosso-Asiatica, vol. 1. p. 165, 1831.
Possibly earlier and unrecorded westward migrations of the brown rat
took place. A few years ago Professor Waile, the archeologist, while
making excavations at Cherchell on the coast of Algeria, dug up the
skull of a rat, which he stated was contemporary with the Roman
occupation of the country under the Cæsars. The skull had but one molar,
much worn, but the cranial bones were intact, and French zoologists
pronounced the remains as undoubtedly those of the “surmulot,” or brown
rat.[D] This shows that we have little more than conjectures for the
early history of this species.
Footnote D:
Comptes Rendus des Séances de L’Académie des Sciences, Paris, vol.
116, p. 1031, 1893.
The brown rat is said to have first appeared in Paris in 1750. It was
brought to the United States, probably from England, about the beginning
of the Revolution, 1775. According to Audubon, it was unknown on the
Pacific coast of the United States in 1851; but Dr. J. S. Newberry
thought it must have arrived at San Diego, Monterey, and San Francisco
at a much earlier date.[E] Doctor Cooper recorded its arrival at Fort
Steilacoom, Washington, as occurring about 1855.
Footnote E:
Pac. R. R. Reports, Vol. 6, Zoological Report, pt. 2, p. 60, 1857.
GENERAL DESCRIPTION.
The brown rat differs considerably from the black rat and the roof rat.
It is larger, has a shorter head, a more obtuse muzzle, smaller ears,
and a relatively shorter and stouter tail. The general color is
grayish-brown above and whitish below. The over hairs of the upper parts
have black tips. The tail is usually shorter than the head and body
combined. The average measurements of adult specimens of the brown rat
in the Biological Survey collections are as follows: Total length, 415
millimeters (16.3 inches); tail, 192 millimeters (7.1 inches); hind
foot, 43 millimeters (1.7 inches). This species sometimes attains a
total length of 19 to 20 inches, and has been known to weigh 24 to 28
ounces and even more. The average weight of an adult brown rat is
considerably less than a pound.
The black rat is less robust than the brown rat. It has a longer head, a
sharper muzzle, and larger and broader ears (fig. 3). The tail is longer
than the head and body combined. The fur is of a sooty, or plumbeous
black, color, paler on the underparts. It is much softer and denser than
that of the brown rat, and the mixture of very dark and lighter over
hairs gives it a peculiar shining appearance. The average measurements
of 20 apparently adult specimens in the collection of the Biological
Survey are as follows: Total length, 379 millimeters (14.9 inches);
tail, 207.4 millimeters (8.1 inches); hind foot, 35.8 millimeters (1.4
inches).
The roof rat in general resembles the black rat, except as to color and
texture of fur. Above it does not greatly differ in color from the brown
rat, but its underparts are usually more yellowish. The fur is commonly
shorter and harsher in texture than that of the black rat, but this
difference might not always be apparent in specimens of the two forms
from the same latitude. The average measurements of 50 adult specimens
of the roof rat in the collections of the Biological Survey are as
follows: Total length, 393.3 millimeters (15.5 inches); tail, 212.8
millimeters (8.4 inches); hind foot, 36.2 millimeters (1.4 inches).
[Illustration:
FIG. 3A, FIG. 3B.—Ears of brown rat and black rat, showing relative
size.
]
Both albinism and melanism are frequent among rats, and pied forms also
are common. It has been claimed that all the white rats (albinos) of the
bird stores are _Mus rattus_, but albinism is by no means confined to
this species. Doctor Hatai found that all the colonies of white rats
maintained at the neurological laboratories of Chicago University and
the Wistar Institute of Anatomy, Philadelphia, were of the _M.
norvegicus_ species.[F] The same is true of all the albino rats in the
collections of the National Museum and the Biological Survey. These
collections contain also several spotted rats (gray and white) and
sooty-black specimens indistinguishable in color from _M. rattus_, all
being undoubtedly of the _M. norvegicus_ species.
Footnote F:
Biological Bulletin, vol. 12, pp. 266–273, March, 1907.
KEY TO THE SPECIES OF MUS IN AMERICA.
Size small. Total length of adult less than 200
millimeters _Mus musculus_
Size large. Total length of adult exceeding 300
millimeters.
Ears moderate, when laid forward barely or not
reaching eye; tail shorter than (rarely equal
to) the length of head and body, darker above
than below; color of body normally gray-brown
above, white below; hind foot 38–46 millimeters _Mus norvegicus_
Ears larger, when laid forward reaching at least
to middle of eye; tail longer than head and
body, dusky all around; hind foot 33–37
millimeters.
Color grayish-brown above, white or yellowish _M. rattus
white below. alexandrinus_
Color blue-black above, slaty below _M. rattus_
HABITS OF RATS.
BREEDING HABITS.
Both climate and food supply affect the rate of multiplication of most
rodents. The rat probably increases more rapidly in a temperate and
equable climate than in one of great variability. Extremes of heat and
cold retard multiplication, decreasing both the number of litters in a
year and the number of young at a time. In northern latitudes,
apparently, more or less interruption of breeding occurs in the winter
months.
Where the country is well settled the food supply of rats is not likely
to be deficient; and when the animals have access to stores of grain,
the young mature very quickly and probably reproduce earlier than when
grain is absent.
The brown rat is more prolific than either the roof rat or the black
rat. The female brown rat has usually 12 mammæ—3 pairs of pectoral and 3
pairs of inguinal—although these numbers are not constant, one or more
teats frequently being undeveloped. The black rat and the roof rat have
only 10 mammæ—2 pairs of pectoral and 3 pairs of inguinal—with but
little tendency to vary. Records of actual observations on the number of
young confirm the deductions that might be drawn from the above facts.
At Bombay, India, during the recent investigations made by the India
Plague Commission, 12,000 rats were trapped and examined. The average
number of embryos found in pregnant brown rats was 8.1; the highest
number, 14. The average for the black rat was 5.2; the largest number,
9.[G]
Footnote G:
Etiology and Epidemiology of Plague, p. 9, Calcutta, 1908.
In temperate latitudes the average number of young produced by the brown
rat is undoubtedly greater. Instances of very large litters observed in
England are recorded in The Field (London). In two instances 22 and 23
young, respectively, were found in a single nest, though no evidence is
offered that these were the progeny of a single female; but in two other
cases 17 and 19 embryos were found in gravid females. A dealer in
feedstuffs in Washington, D. C., relates that he found 19 young rats in
a single nest in his store. Within the past few months the writer has
examined four pregnant brown rats taken in traps. The numbers of embryos
they contained were 10, 11, 11, and 13, respectively. While we have not
enough data for definite conclusions, we may safely state that the
average litter for this latitude is not less than 10.
Frank T. Buckland, in Curiosities of Natural History, relates that a
white rat which he kept in captivity gave birth to 11 young when only
eight weeks old. As gestation in rats occupies three weeks, this animal
must have bred when only five weeks old.
The number of times rats breed in a year is not definitely known, and
probably varies considerably with local conditions. Kolazy makes the
almost incredible statement that two female white rats, kept by him in
confinement and well fed, within thirteen months gave birth to 26
litters of young, numbering 180 in all. One of them produced young
regularly at intervals of 25 days.[H]
Footnote H:
Verh. Zool. Bot. Gesel. Wien., pp. 731–734, 1871.
The writer recently kept two young female brown rats with a male in a
large open cage for several months. One of the females gave birth to
young on April 15; the other on April 17. The number in these litters
was not observed, as some were devoured soon after birth, and all within
three days, presumably by the male rat. On May 23 both females gave
birth to young, 24 in number, all in one nest.
The known facts concerning the breeding of the brown rat may be briefly
summarized as follows: The animals breed from three to five times a
year, each time bringing forth from 6 to 19 young. After a gestation
period of twenty-one days, the females give birth to their young in
nests built in underground burrows or under floors, stacks, lumber,
woodpiles, or other shelter. The young are blind and naked when born,
but grow rapidly, and young females are capable of breeding when less
than three months old.
Early spring and summer are the periods of greatest reproductive
activity among rats. Young, however, are to be found every month of the
year.
The above statements apply in the main also to the black and the roof
rat, but the number of young in a litter is somewhat smaller. The newly
born young of the black rat have not the bright pink color of those of
the brown and the roof rat, but are bluish, especially on the upper
parts. Black-and-white spotted rats are at first bluish-and-red spotted,
the red areas representing the white of the adults.
ABUNDANCE OF RATS.
From the foregoing account of the breeding habits of rats, the great
difficulty of ridding cities or large areas of the animals may be
readily understood. Ordinarily, they breed more rapidly than they are
destroyed. Although few are seen in daytime, at night they fairly swarm
along river fronts and wharves, as well as in sewers, stables,
warehouses, markets, and other places where food is abundant. Their real
numbers may sometimes be discovered when any such harbor is demolished.
An ordinary farm sometimes supports an astounding number of rats. In
1901, an estate of 2,000 acres near Chichester, England, was badly
infested with the pests. They were systematically destroyed by traps,
poisons, and ferrets, under the supervision of the proprietor. In this
way 31,981 were killed, while it was estimated that tenants at the
thrashing had destroyed fully 5,000 more. Even then the property was by
no means free from rats.[I]
Footnote I:
The Field (London), vol. 100, p. 545, 1902.
During a plague of rats on the island of Jamaica in 1833, the number of
rats killed on a single plantation in a year was 38,000. The injury to
sugar cane on the island caused by the animals was at that time
estimated at half a million dollars a year.[J]
Footnote J:
New England Farmer, vol. 12, p. 315, 1834.
The report of the Indian Famine Commission presented to the English
Parliament in 1881 affords one of the best illustrations of the number
of rats that may infest a country. An extraordinary number of the
animals at that time inhabited the southern Deccan and Mahratta
districts of India. The autumn crop of 1878 and the spring crop of 1879
were both below the average, and a large portion of each was destroyed
by rats. The resulting scarcity of food led to the payment of rewards
for the destruction of the pests, and over 12,000,000 were killed.[K]
Footnote K:
British Medical Journal, Sept. 16, 1905, p. 623.
MIGRATIONS AND INVASIONS.
Migrations of rats have often been recorded. The brown rat is known in
Europe quite generally as the migratory rat. The Germans call it the
Wanderratte. Pallas narrates that in the autumn of 1727 this species
arrived from the east at Astrakhan, southeastern Russia, in such great
numbers and so suddenly that nothing could be done to oppose them. They
crossed the Volga in immense troops. The cause of this general migration
was attributed to an earthquake; but since similar movements of the same
species often occur without earthquakes, it is probable that only the
food supply of the animals was involved in the migration which first
brought the brown rat to Europe.
A seasonal movement of rats from houses and barns to the open fields
takes place in spring when green and succulent plant food is ready for
them. The return movement takes place in the autumn. This seasonal
migration is noticeable even in large cities.
But more general movements of rats frequently occur. In 1903 a multitude
of migrating rats spread over several counties in western Illinois. They
were noticed especially in Rock Island and Mercer counties. For several
years previous no abnormal numbers of the animals were seen, and their
coming was remarkably sudden. An eyewitness to the occurrence informed
me that as he was returning to his home one moonlit night he heard a
general rustling in a nearby field, and soon a great army of rats
crossed the road in front of him, all moving in one direction. The host
stretched away as far as they could be seen in the dim light. These
animals invaded the farms and villages of the surrounding country and
caused heavy losses during the winter and summer of 1904. A local
newspaper stated that between March 20 and April 20, 1904, Mr. F. W.
Montgomery, of Preemption, Mercer County, killed 3,435 rats on his farm.
He caught most of them in traps.[L]
Footnote L:
Moline (Ill.) Evening Mail, Apr. 25, 1904.
In 1877 a similar migration of rats into parts of Saline and Lafayette
counties, Mo., took place.[M] Also, one came under my own observation in
the Kansas River valley in 1904. This valley, for the most part, was
flooded by the great freshet of June, 1903, and for about ten days was
covered with several feet of water. Probably most of the rats in the
valley at the time perished in the flood. Yet in the fall of 1903 much
of the district was visited by hordes of rats, which remained during the
winter and had so increased by the following spring that serious losses
to grain and poultry resulted.
Footnote M:
Forest and Stream, vol. 8, p. 380, July 12, 1877.
No doubt most of the so-called migrations of rodents, were all the facts
known, could be accounted for as instances of abnormal reproduction or
of failure of food supply in one place, compelling change of habitat. In
England a general movement of rats inland from the coast occurs every
October. This is known to be closely connected with the closing of the
herring season. During the fishing the rodents swarm to the coast,
attracted by the offal left in cleaning the herring; and when this food
fails, the animals troop back to the farms and villages.
In South America plagues of rats are often periodical, occurring in
Parana, Brazil, at intervals of about thirty years and in Chile at
intervals of from fifteen to twenty-five years. It has been discovered
that these plagues in the cultivated lands follow the ripening and decay
of the dominant species of bamboo in each country. The ripening of the
seed furnishes for two or more years a favorite food for rats in the
forests, where the animals multiply greatly. When this food fails, they
are forced to the cultivated lands for subsistence. In 1878 almost the
whole crops of corn, rice, and mandioca in the State of Parana were
destroyed by rats, causing a serious famine.[N]
Footnote N:
Nature, vol. 20, p. 65, 1879.
An invasion of rats (_Mus rattus_) in the Bermuda Islands occurred about
the year 1615. Within two years they had increased so alarmingly that
none of the islands was free from them. The rodents “devoured everything
that came in their way—fruits, plants, and even trees”—so that for a
year or two the people were nearly destitute of food. A law was passed
requiring every man in the islands to keep 12 traps set. In spite of all
efforts the animals continued to increase, until finally they
disappeared so suddenly that they must have been victims of a
pestilence.[O]
Footnote O:
Popular Science Monthly, vol. 12, p. 376, January, 1878.
FOOD OF RATS.
Instead of being strictly herbivorous, as might be inferred from their
dentition, rats are practically omnivorous.
The bill of fare of the rat includes grains and seeds of every kind,
flour, meal, and all food products made from them; fruits and garden
vegetables; mushrooms; bark of growing trees; bulbs, roots, stems,
leaves, and flowers of herbaceous plants; eggs, chicks, ducklings,
squabs, and young rabbits; milk, butter, and cheese; fresh meat and
carrion; mice, rats, fish, frogs, mollusks, and crustaceans. This great
variety of food explains the ease with which rats maintain themselves in
almost any environment.
FEEDING HABITS.
Rats resemble squirrels in the manner of holding food while eating. As
soon as they have separated a small portion of food from a larger mass,
they sit up, arching the back and holding the morsel in the paws and
turning it as a squirrel does. After eating, they brush the mouth and
fore parts, including the whiskers (vibrissæ), with the paws until all
are clean. Rats drink much water, a habit often taken advantage of in
placing traps or poisons for them.
Rats generally feed after sunset, but in places where they are not often
disturbed they come out and feed in broad day and even in the sunshine.
The roof rat and the black rat are more expert climbers than the brown
rat, which is larger and clumsier. In buildings, the brown rat keeps
mainly to the cellar and lower parts, where it commonly lives in
burrows. From these retreats it makes nightly excursions to the upper
parts of the house in search of food. The roof rat and the black rat
live in the walls or in the space between ceilings and roofs. They nest
in any of these places.
Rats readily climb trees to obtain fruit. In the Tropics the roof rat
and the black rat habitually nest in trees and spend much of their time
in these arboreal retreats, while the brown rat makes only occasional
excursions into the branches in search of food.
In the open, rats seem to have defective vision by daylight. They move
slowly and uncertainly. On the contrary, at the side of a room and in
contact with the wall they run with great celerity. This fact suggests
that the vibrissæ serve as feelers and that the sense of touch in them
is extremely delicate. The animals always prefer narrow spaces as
highways—another circumstance which may be made use of in placing traps.
FEROCITY OF RATS.
The ferocity of rats has been grossly exaggerated. The stories of their
attacks upon human beings, sleeping infants especially, have but slight
foundation. If attacked, nearly all rats defend themselves with the
teeth; and no doubt a horde of rats, if hungry, would be formidable.
Ordinarily the probability of being bitten by rats is remote, and the
bite is not poisonous.
The ferocity of rats is mainly exercised against members of their own
order. The brown rat is undoubtedly the most formidable of the genus in
America, and possibly in the world; yet when captured it adapts itself
readily to confinement, and in a few days will take food and water
whenever offered. The enmity of this species toward other rats and mice
is well known. It is supposed to have destroyed the black rat over the
greater part of Europe and America, although it is possible that disease
carried by the brown rat was a factor in the disappearance of the other
species. That the black and the roof rat in tropical countries have not
been displaced by the brown rat is probably owing largely to their more
arboreal habits. It is not uncommon in the Far East to find two species
of rats living side by side in the same locality. An example is _M.
imperator_ and _M. rex_ living on one of the Solomon Islands. The first
is a burrowing species; the other arboreal. In 1877 two native species
of rats, _M. macleari_ and _M. nativitatis_, were found living together
in amity on Christmas Island, in the Indian Ocean.[P] About ten years
ago the brown rat was accidentally introduced, and it is now thought
that both the native species are extinct.
Footnote P:
Proc. Zool. Soc. 1888, pp. 517, 534.
When pressed by hunger rats become cannibals and destroy their weaker
fellows. However, when ordinary food is abundant, cannibalism among rats
is rare.
PLAGUE INFECTION IN RATS.
By GEORGE W. MCCOY,
_Passed Assistant Surgeon United States Public Health and
Marine-Hospital Service._
The rat is a known or a suspected factor in the transmission of several
diseases, yet at present, and perhaps for many years to come, the most
immediate and pressing question that concerns us is its relation to the
origin and spread of plague among human beings. For this reason a
discussion of the reaction of these animals to natural and to artificial
infection with _B. pestis_ becomes of prime importance.
Not only are rats believed to be more or less directly responsible for
cases of human plague in a community, but in addition, they are believed
to be the most frequent medium through which plague is carried from one
locality to another, for these animals are good travelers, can live on a
very meager ration, and can do without water for a long time if food is
available. We have found that on a diet of dry grain alone a rat may
live for over a month.
In this connection it may not be amiss to call attention to the
importance of the rat as an agent in conveying plague infection to other
rodents and especially to ground squirrels. There is every reason for
believing that the infection among the squirrels in California was
derived originally from rats. Wherry[16] states that more rats than
ground squirrels have been trapped in the squirrel burrows in the
vicinity of Berkeley, Cal. This shows how easy it might be for rats to
infect squirrels and vice versa.
The clinical manifestations of plague in rats are of little importance.
It is generally said that the plague-infected rat staggers about with a
drunken gait, loses fear of its natural enemies, and is readily
captured. Our experience with artificially infected rats indicates that
the animals show no marked manifestations of illness until shortly
before death when they become quiet, crouch in the corner of the cage,
and try to hide.
It is rather surprising to observe that comparatively few plague rats
are found dead. In the San Francisco campaign, while no accurate figures
are obtainable, certainly not more than 20 per cent of the infected
rodents were found dead, the remainder being trapped. This is probably
due to the fact that the disease is one of several days’ duration, from
two to six most frequently, and during this period there are more
chances of catching the sick rodent in a trap than there are of finding
the body after death, unless the immediate surroundings are known to
harbor infected animals and an especially careful search is made for
cadavers in the places, often difficult of access, where rats have their
burrows and nests.
As plague is a disease that gives rise to such characteristic gross
pathological lesions in man and in laboratory animals, it is but
reasonable to expect that equally distinctive lesions would be found in
the rat, and this we find to be the case.
Skschivan[1], Kister and Schumacher[2], and other writers have observed
and recorded the gross lesions of plague in rats. It remained, however,
for the Indian Plague Commission[3], which had the opportunity of
examining an enormous number of plague rats in Bombay and elsewhere in
India, to crystallize our knowledge of this subject and to point out its
field of usefulness.
As to the comparative value of microscopical and macroscopical methods
of diagnosis, the Indian Plague Commission[3] states that: “The results
of tests carried out for the purpose of comparison make it manifest that
the naked eye is markedly superior to the microscopical method as an aid
in diagnosis, and as the result of our experience we are prepared to
make a diagnosis of plague on the strength of the macroscopical
appearances alone, even though the other results of cutaneous
inoculation and culture are negative and the animal shows signs of
putrefaction.”
Our experience with rat plague, though limited, leads us to the same
conclusion as that arrived at by the Indian Commission in regard to the
value of the gross lesions of plague in making the diagnosis. To one who
is acquainted with them, these lesions are as characteristic as those of
any infectious disease in man. It is quite true that occasionally
atypical cases are encountered where the majority of the gross lesions
are wanting, and in such cases it becomes necessary to resort to the
inoculation of animals or to cultural investigations in order to make a
diagnosis. Such cases are, however, if anything, rarer than are atypical
post-mortem findings in pneumonia or in typhoid fever in man.
MODE OF EXAMINATION.
A brief description of the actual manner of examining rats for plague
infection will be given here.
The rats are immersed in any convenient solution for the purpose of
killing fleas and other ectoparasites that might be capable of carrying
infection from a plague-infected rat.
The following plan of handling rats has been found satisfactory in the
federal laboratory at San Francisco. The rats are nailed to a shingle by
an attendant. Another attendant reads off the address on the tag
attached to the rat, puts a check number on the shingle, and records the
address from which the rat was taken and the check number on the card
shown on page 48. This card is arranged so as to give the data as to the
address from which the rat came, its size, sex, and species. After being
checked the rats are dissected and finally, after examination by the
medical officer, they are removed from the shingle; any plague-infected
rats are burned as soon as the necessary investigation has been made.
The dissection is made by reflecting the skin from the whole front of
the body and neck so as to expose the cervical, axillary, and inguinal
regions. The thoracic and abdominal cavities are then opened with
scissors.
In the inspection, careful search for buboes must be made in the regions
of the various peripheral lymph glands. The abdominal and thoracic
organs must be subjected to a careful scrutiny. It is needless to say
that this work should be done in a rat-proof, well-lighted building that
is provided with water, gas, and sewer connections. The utmost care
should be taken to avoid any undue risk of infection. The wearing of
rubber gloves is not necessary. Everyone who has to handle infected
animals must be sufficiently alive to the danger of infection.
In the extensive work conducted by the Indian Plague Commission[3],
attendants were protected with Haffkine’s prophylactic. This is
undoubtedly a wise precaution and should be taken if possible.
For a worktable on which to dissect the rats we use in San Francisco a
table which slopes gently from the sides and ends toward the center,
where a drain pipe is attached which leads to a vessel containing a
disinfectant. The table is covered with sheet lead.
The layman of average intelligence readily learns to recognize the gross
lesions of rat plague and it is wise to train the laboratory attendants
to do this. Every rat should, however, be subjected to a careful
scrutiny by the physician responsible for the work. The great majority
of rats may be put aside after a cursory examination as entirely beyond
suspicion of infection. Probably 8 or 10 per cent of them will require a
very careful examination for the gross lesions of plague. A card which
we have found very useful for keeping records of suspected and infected
animals is shown on page 34. Probably all of the species of the genus
_Mus_ are susceptible to plague infection. I shall, however, confine
myself to a consideration of plague in the rats found the world over
(_M. norvegicus_, _M. rattus_, _M. alexandrinus_).
In Bombay[18] it has been found that the epizootic among _Mus
norvegicus_ appears first and is probably responsible for the diffusion
of plague among _Mus rattus_. It precedes the infection among _Mus
rattus_ by about ten days, and the opinion is expressed by the Indian
Plague Commission that the usual course of the infection is from the
_Mus norvegicus_ to the _Mus rattus_, and as the latter rodent is a
house dweller in India it is the most frequent source of human
infection.
In San Francisco the _Mus rattus_ population is comparatively small,
contributing perhaps 2 per cent of the total rat population of the city;
but in the section of the city where the large warehouses are found,
especially those where oriental goods are stored, about 15 per cent of
the rats taken are _Mus rattus_. So far as concerns plague infection
about 5 per cent of the rat cases were in _Mus rattus_. It may be of
interest to note that the last infection found among rats in San
Francisco was among the _Mus rattus_ in a large warehouse near the water
front. Two plague-infected rats were found in this building, one October
21, 1908, and the other October 23, 1908. A large number of mummified
carcasses, all _Mus rattus_, were found in the building, and it seems
not unlikely that a somewhat extensive epizootic had occurred among
them. No previous case of rat plague had been found in the city for
eighty-five days, though about 25,000 rats had been examined during that
period, and none have been found in the six months since, although over
30,000 rats have been examined. Our records show that of 84 infected
rats, 79 were _Mus norvegicus_, and the remainder were _Mus rattus_.
Some of the latter may have been _Mus alexandrinus_, as the two species
(_Mus rattus_ and _Mus alexandrinus_) were not clearly differentiated in
the earlier examinations.
THE GROSS LESIONS OF NATURAL RAT PLAGUE—ACUTE PLAGUE.
SUBCUTANEOUS INJECTION.
This is the sign which usually first attracts attention. White[4], in
discussing plague in rats, states that “the most noticeable post-mortem
appearance of the plague rat is the engorgement of the subcutaneous
blood vessels, together with a diffuse pink color of the subcutaneous
muscles, which have a peculiar dry, waxy translucency.” It has been our
experience frequently to have an attendant who is dissecting rats remark
that he had found an infected rat after the first incision was made in
reflecting the skin. The injection is dark red, and upon close
inspection one sees that the small vessels are uniformly distended with
blood. It is usually distributed over the whole surface of the body, but
on two occasions we have seen it confined to the side of the body on
which the primary bubo was found. A bright pink injection is a rather
common finding among rats in San Francisco. It is not likely to be
mistaken for the injection of plague infection. Subcutaneous œdema,
confined to the vicinity of the bubo, is occasionally encountered.
In our experience in San Francisco an injection identical in appearance
with that found in plague infection was found only twice, and in each
case there was associated with it a small discharging subcutaneous
abscess. There were no other lesions in either case and the pus from
these abscesses failed to produce plague in guinea pigs.
In a series of 61 consecutive plague rats in San Francisco, injection
was present fifty-two times, it was confined to the region of the bubo
twice, it was unilateral twice, and was general in distribution
forty-eight times. It was slight thirteen times, moderate fifteen times,
marked sixteen times, intense eight times.
THE BUBO.
This is the most reliable single sign of plague infection, and when
present in typical form is enough on which to base a diagnosis which
rarely proves erroneous.
The gland involved is usually surrounded by a more marked injection than
is present elsewhere, and an infiltration which at times is hemorrhagic.
This surrounding hemorrhage which was common in the plague rats
described by the Indian Plague Commission was met with very rarely in
San Francisco. The gland proper is usually caseous. The contents may be
shelled out very readily, though prior to section the gland feels very
firm. In the cases seen at the federal laboratory in San Francisco, the
contents of the buboes were recorded as being hemorrhagic four times and
as caseous twenty-nine times. Pest-like bacilli were noted as present in
18 cases, in 6 of which the “coccoid” form predominated. They were
recorded as absent five times.
Indolent enlargement of the lymph glands is very commonly encountered in
rats that are not infected with plague. Among old rats probably 15 per
cent will show this. Such glands, however, are tough, elastic, and not
surrounded by infiltration. They are not likely to be mistaken for the
plague buboes. In the leprosy-like disease of rats, the glands may reach
an enormous size.
Observers differ as to the location of the primary bubo. Skschivan[1]
states definitely the location of five primary buboes in plague rats
seen in Odessa in 1901. Two were in the axilla, two in the inguinal
region, and one in the neck. Kitasato[5] says: “To judge from the
experience of the past it can be suggested that in examining rats
particular attention should be paid to their submaxillary and cervical
glands and to the spleen. These organs in most cases show the evidence
of infection, if there be any.” From this it would appear that he
regarded the neck glands as the most frequent seat of the bubo. It may
be remarked here that his experience was derived from plague rats seen
in Asia.
We find a marked difference between the experience in San Francisco and
that in Bombay. This is demonstrated in the following table, which shows
the location in percentage of single buboes in each situation:
───────────────────────────────────────┬───────┬───────┬───────┬───────
│ Neck.│Axilla.│ Groin.│Pelvis.
───────────────────────────────────────┼───────┼───────┼───────┼───────
│ _Per│ _Per│ _Per│ _Per
│ cent._│ cent._│ cent._│ cent._
Indian Plague Commission, Bombay—2,923 │ 75│ 15│ 6│ 4
rats[3] │ │ │ │
Wherry, Walker, and Howell, San │ 12│ 12│ 75│
Francisco[6]—8 rats │ │ │ │
Federal laboratory, San Francisco—32 │ │ 22│ 72│ 6
rats │ │ │ │
───────────────────────────────────────┴───────┴───────┴───────┴───────
The American figures are too small to be of much significance, but one
is struck with the fact that in Bombay three-fourths of the buboes are
in the neck, while in San Francisco three-fourths of all found are in
the inguinal region. We have records of only three multiple buboes found
in rats in San Francisco, and in no case was either of the buboes in the
neck; while in Bombay, to quote from the report[3], “Of the rats with
multiple buboes 54.5 per cent had a bubo in the neck.” Striking as these
figures are, we have collected further evidence that the inguinal region
is the commonest location of the bubo in plague rats in this vicinity.
Passed Asst. Surg. J. D. Long, Public Health and Marine-Hospital
Service, who has had an extensive experience with rat plague in Oakland,
Cal., tells me that the majority of the buboes were found in the groin,
very few in the neck. Acting Assistant Surgeon Wherry, Public Health and
Marine-Hospital Service, informs me that in a series of plague rats
examined after the report made in association with Walker and Howell[6],
the cervical bubo was very rarely encountered.
Particular care was taken to look for cervical buboes, as it seemed
rather inconsistent to find the other lesions so fully in accord with
those found in India, yet to have the location of the bubo to differ so
radically. We have not encountered a mesenteric bubo in our work in San
Francisco. The Indian Plague Commission found none in over 5,000
naturally infected plague rats. As mesenteric buboes are very commonly
encountered in plague infection brought about by feeding, they conclude
that the absence of these buboes in naturally infected rats is strong
evidence that the infection does not enter by the alimentary canal.
THE GRANULAR LIVER.
Two lesions of the liver are encountered in plague rats. The one most
frequently observed is spoken of by the Indian Plague Commission as
“fatty” change, though it is explained that this term refers to the
naked eye appearance as, microscopically, the lesion is found to be due
to a necrosis of the liver tissue. When this change is present the organ
is found to be rather yellowish in color and is studded with an enormous
number of yellowish white granules which are about the size of a pin
head. This lesion, which was very common in the San Francisco cases, is
very readily recognized.
The other lesion is a marking of the organ with grayish white spots;
“they are typically of the size of a pin’s point, and give the surface
of the organ a stippled appearance as if dusted over with gray
pepper”[3] (p. 331). This appearance, which is less frequently
encountered than is the preceding one, is more difficult to recognize;
indeed the most careful scrutiny is necessary to avoid overlooking it.
Rats that have been fed with certain biological preparations used to
destroy rodents (Danysz’s virus and similar preparations) often present
lesions in the liver resembling those due to plague infection. The
granules are, however, larger and more distinct. In these cases the
spleen is enlarged and generally granular, but rarely dark and friable
as in plague infection.
THE SPLEEN.
The size of the spleen of healthy rats of the same weight varies so
greatly that often one can not be sure as to what constitutes an
enlargement of this organ.
In plague rats this organ is markedly enlarged, firm, friable, rather
dark in color, and occasionally presents small granules under the
capsule. As Skschivan[1] pointed out, these granules are not encountered
as often as are granules in the liver. At times the organ presents a
very distinctly mottled appearance. This latter appearance is much more
frequently seen in artificially inoculated rats than in those found
infected in nature. We have seen the organ distinctly slate-colored on
several occasions.
PLEURAL EFFUSION.
The last sign of rat plague is one of great importance when associated
with other suspicious lesions. The effusion is bilateral, and is serous
in character, usually clear, though it is occasionally blood stained.
Pleural effusion is rarely found in rats other than those that are
plague infected. The following table shows in percentage the frequency
of the various macroscopical lesions of acute natural rat plague, as
observed in Bombay and in San Francisco:
────────────────────────┬────────────┬──────┬────────┬───────┬─────────
│Subcutaneous│Bubo. │Granular│ Large │ Pleural
│ injection. │ │ liver. │ dark │effusion.
│ │ │ │spleen.│
────────────────────────┼────────────┼──────┼────────┼───────┼─────────
│_Per cent._ │ _Per │ _Per │ _Per │ _Per
│ │cent._│ cent._ │cent._ │ cent._
Indian Plague │ 69 │ 85 │ 58 │ │ 72
Commission, │ │ │ │ │
Bombay—4,000 rats │ │ │ │ │
Wherry, Walker, and │ 59 │ 14 │ 14 │ 68 │ 71
Howell, San │ │ │ │ │
Francisco—88 rats │ │ │ │ │
Federal laboratory, San │ 85 │ 57 │ 87 │ 74 │ 59
Francisco—62 rats │ │ │ │ │
────────────────────────┴────────────┴──────┴────────┴───────┴─────────
It is recognized that the data from the San Francisco records is so much
smaller than that from the Indian report that perhaps no just comparison
is to be made. However, the figures are quite similar, except for the
small percentage of buboes and of liver lesions in the work of Wherry,
Walker, and Howell. The work of these observers was done in the early
part of the epizootic in San Francisco while the other figures from that
city are drawn from records later in the campaign.
No single sign is pathognomonic, though only once have we been deceived
by what was regarded as a typical plague bubo. This was in a rat that
presented no other suspicious lesions and the inoculation test resulted
negatively.
It is a combination of two or more of the signs that is of moment. The
subcutaneous injection with a typical liver or these signs associated
with a typical spleen afford good grounds for a diagnosis. A rat showing
a typical liver associated with a pleural effusion will usually prove to
be plague infected, and if a large, dark, firm spleen is also found a
diagnosis may be considered as practically established.
As has been pointed out by several writers gross lesions of plague may
be distinguished even in rats that are badly decomposed.
CHRONIC PLAGUE.
No case of natural chronic plague has been encountered in San Francisco.
Only one case was found among the many hundreds of plague rats examined
by the Indian Plague Commission[3] (p. 457) in Bombay. However, this
commission encountered a considerable number of cases among _Mus rattus_
in the Punjab villages of Kasel and Dhand. The lesions were purulent, or
caseous foci. They classify these cases as follows: Chronic plague of
the visceral type, which is further subdivided into splenic nodules and
abscesses, and mesenteric abscesses; chronic plague of the peripheral
type in which abscesses are situated in the regions of the peripheral
lymph glands.
Plague bacilli were either absent or very scanty upon microscopical
examination. They were, however, quite frequently recovered by cultural
methods, and in the great majority of the cases the organisms were fully
virulent. No evidence was forthcoming to show that this chronic rat
plague had anything to do with the recurrence of acute plague among the
rats.
We have diligently sought for chronic plague among the rats in San
Francisco, but, as we said above, without success, although a
considerable number of lesions that correspond perfectly to the
description of chronic plague have been submitted to the guinea-pig
inoculation test, but invariably with a negative result. An account of
the lesions of chronic plague as observed among inoculated rats is given
in another part of this paper.
Pound[7] believes that recovery from plague in rats is shown by the
presence of pigmented lymphatic glands. Kister and Schumacher[2] mention
pigment deposits in the inguinal region, but remarked that they are not
characteristic of plague, a view which I believe is correct, as we have
frequently seen them in San Francisco among the older rats, in which
there was no reason to suspect previous plague infection, and they have
been almost uniformly absent in the case of rats that have been
experimentally infected with plague but have recovered.
RAT PLAGUE WITHOUT GROSS LESIONS.
Plague infection may be present in a rat without bringing about any
recognizable gross lesions. For example: Dunbar and Kister[8] mention a
rat, which came from a ship on which plague rats had been found, that
had no lesions, and cultures were negative; but a guinea pig cutaneously
inoculated died of plague.
Among a considerable number of inoculated rats we have very rarely,
perhaps once or twice in a hundred cases, found nothing at the
post-mortem examination that would suggest plague infection, yet
cultures or inoculation of guinea pigs would demonstrate the presence of
_B. pestis_. Such cases are very infrequent, but it should be kept in
mind that they do occur. When a large number of rats are to be examined
it would be impracticable to inoculate a guinea pig from each rat; and
even if one did this the occasionally resistent guinea pig would
introduce a larger error than exists by placing dependence upon the
gross lesions for a diagnosis.
MICROSCOPICAL EXAMINATION.
The exact weight to be given to the morphology of the organisms found in
smears from the organs of a rat suspected of being plague infected is a
matter of individual judgment. Smears from a bubo and from the spleen
may show no organisms at all, or none even remotely resembling _B.
pestis_, and yet by culture and inoculation methods we may be able to
demonstrate that the animal is plague infected. Attention has been
called to this point by several observers, and every worker in this
field has the experience sooner or later.
In other cases the smears will show such numbers of perfectly typical
bipolar bacilli and “involution” (coccoid) forms as to leave scarcely
any doubt as to the nature of the organism. But even here cases that are
not plague are encountered that will deceive even the most experienced.
We have been accustomed to put great dependence on the “coccoid” forms
of the organism, but late in the San Francisco experience, smears from a
splenic nodule that was not regarded as due to plague showed perfectly
typical “involution” (“coccoid”) forms. Animal inoculations and cultures
showed that the tissues contained no plague bacilli.
In addition to these two classes of cases we have a third, where smears
show a few typically shaped bacilli, or where a considerable number of
typical-looking bacilli are found along with many other bacterial forms.
There is no safe rule for reaching a conclusion in these cases, and one
must resort to culture or to inoculation methods, or both. In any such
case it is always a good plan to let the macroscopical findings have
more weight than the microscopical.
The bipolar appearance of _B. pestis_ is so largely dependent upon the
technique of staining, fixing, length of time the stain is allowed to
act, and the length of the washing, that it should never be given great
weight. Here, as elsewhere in bacteriology, many errors are to be
avoided by not depending too much upon the morphology of the organism
under investigation.
BACTERIOLOGICAL DIAGNOSIS OF RAT PLAGUE.
While the gross lesions of rat plague are often sufficiently
characteristic to justify a positive diagnosis, and the gross lesions in
conjunction with the microscopical examination will in other cases
enable us to say definitely that a rat is plague infected, still a
certain number of cases occur in which it is necessary to resort to
other methods, and there are circumstances, such as the first case in a
community, that make a complete bacteriological confirmation of a
diagnosis necessary.
This is not the proper place in which to discuss fully the bacteriology
of plague. However, a brief outline of what is necessary to establish
beyond question the existence of plague infection in an animal will be
given.
_B. pestis_ may often be isolated in culture from the tissues (bubo,
liver, spleen, or heart’s blood) of an infected rat. Unless the tissues
are badly contaminated with other organisms, plate or stroke culture
will yield a growth of _B. pestis_ in pure culture, or isolated
pest-like colonies may be transferred to other media.
It is unwise, however, to trust to cultural methods alone. In the
majority of doubtful cases it is advisable to inoculate guinea pigs or
white rats. The lesions of plague in these animals are quite
characteristic, and _B. pestis_ may readily be recovered from their
tissues if cultures are made at once after death.
A pure culture of the organism under suspicion is obtained from the
naturally infected animal or from a laboratory animal inoculated from
the one under suspicion. This culture is studied in regard to its
morphology; first, on agar, where it grows as a short rod, or often in
the shape of a coccus; second, in broth, where it often grows in
streptococcus-like chains; third, on agar containing 3 per cent sodium
chloride, where most extraordinary alterations in morphology occur,
giving large balloon-shaped bodies, objects resembling gigantic cocci
and enormous trypanosome-shaped forms, the so-called “involution” forms.
These involution forms must not be confused with the so-called
“involution” (coccoid) forms of the organism found in smears from animal
tissues.
We think it worth while to call special attention to the great
diagnostic value of involution forms developed when _Bacillus pestis_ is
grown on salt agar. No other organism that we have had the opportunity
of working with gives forms that are at all likely to be mistaken for
those of _Bacillus pestis_, except _B. mallei_, and of course the other
points of difference would at once serve to distinguish the latter
organism.
_B. pestis_ is Gram negative, though this point is of no great value
except to distinguish the “coccoid” forms from pus cocci.
The appearance and character of the culture should be as follows:
_Agar._—Smooth, glistening, round whitish colonies which are found to be
sticky when touched with an inoculating needle.
_Broth._—A scanty surface growth which falls, often in globular masses,
when the tube is gently agitated; and a fine flocculent precipitate.
_Litmus milk._—Generally rendered slightly acid.
_Glucose broth._—Rendered slightly acid. Gas is not formed.
_Lactose broth._—Unchanged in reaction. Gas is not formed.
The other cultural reactions are of no material assistance in the
identification of the organism. Indeed, in routine work the appearance
of the growth on agar and in broth, together with the involution forms
on salt agar, are sufficient for identifying the organism.
The plague bacillus is a nonmotile organism, a point worth bearing in
mind.
A culture answering the above description when rubbed into the shaven
skin of a guinea pig or a white rat should cause the death of either of
these animals of plague within ten days, and an organism must be
isolated from their tissues after death corresponding to the one
inoculated.
If one wishes to be doubly certain, one may inoculate a series of
laboratory animals, giving to half of them a sufficient dose of antipest
serum. The protected animals should recover, or markedly outlive the
controls, which should die in the usual time.
As to the virulence of cultures of the bacillus from cases of rat plague
Klein[17] states “that _B. pestis_ bred in the rat is of decidedly less
virulence than that bred in the human subject; moreover, the former is
liable, outside the animal body, to a much greater extent to rapidly
lose its virulence.” It is evident that in any given epidemic it will be
very difficult to say just which strain, rat or human, one is dealing
with.
In the case of the strains of _B. pestis_ recovered from rats in San
Francisco we have seen nothing to justify such an opinion as Klein
expresses. The cultures are all highly virulent and retain their
virulence under artificial cultivation.
The value of inoculation by the cutaneous method to demonstrate the
presence of plague infection in putrefying tissue is well known. We have
had one example in which the value of inoculation by this method was
proven in the case of a rat that was so badly decomposed as not to admit
of any opinion being formed as to whether the animal was infected or
not. A rat was brought from a warehouse where a typical plague rat had
been taken a few days previously. The specimen was so badly decomposed
that the abdominal organs could not be distinguished with any degree of
certainty. Smears from tissue that was thought to represent spleen were
negative so far as pest-like organisms were concerned. A guinea pig
vaccinated from this splenic material died in seven days of typical
plague, and a pure culture of _B. pestis_ was obtained from its organs.
Kolle and Martini [9] compare the cutaneous method of inoculation to the
use of an agar plate in separating plague bacilli from other organisms,
and so regularly does _B. pestis_ penetrate the skin and infect the
animal, and so rarely do other organisms do this, that it offers a
certain and accurate method of “filtering out” _B. pestis_ from any
badly decomposed tissue.
The technique of the cutaneous method of inoculation, or “vaccination”
as it is sometimes called, is very simple. An area about an inch square
is shaven on an animal’s belly, taking care to abrade the epithelium
slightly. The culture or suspected tissue is rubbed on this shaven area
with a platinum loop or a dressing forceps. Guinea pigs when inoculated
in this manner generally die before the seventh day; white rats die a
day or two earlier.
Kister [10] uses a drop of juice from an organ rich in bacilli for
agglutination experiments with antipest serum. This would appear in many
cases to be of very material assistance, and the objection that it is
difficult to form a uniform emulsion of the bacteria would be avoided.
The well-known tendency of _B. pestis_ to grow in clumps in culture is
the main reason why agglutination reactions have not been more
extensively used in plague work.
Skschivan [1] makes use of Pfeiffer’s phenomenon in establishing the
identity of a given organism as _B. pestis_.
To assist in the early diagnosis of plague, Dunbar and Kister [8]
practiced intraperitoneal inoculation of laboratory animals and used a
parallel series of immunized animals. As is well known, intraperitoneal
inoculation with plague cultures or infected material leads to the early
death of the inoculated animal, and it is evident that the survival of
the immunized animal would afford considerable evidence that the
material used for inoculation contains _B. pestis_.
PEST-LIKE BACTERIA FOUND IN RATS.
The somewhat general impression that there are a considerable number of
organisms that are readily mistaken for _Bacillus pestis_ is not
justified, provided one gives attention to cultural and inoculation
investigations. It is quite true that there are a considerable number of
organisms which in smears from tissues are scarcely to be distinguished
_morphologically_ from _B. pestis_. The similarity, however, usually
ends there. A few resemble plague somewhat closely in cultural
reactions, and especially _B. pseudo-tuberculosis rodentium_ (Pfeiffer)
should be mentioned here; but these differ in pathogenicity. For
example, the above-named organism is not pathogenic for rats.
Neumans[11] reviews the subject of pest-like organisms pathogenic for
rats, and describes an organism belonging to this group which he
isolated from the body of a rat. His work clearly shows that none of the
organisms that have been described should cause any serious difficulty
in the hands of a careful investigator.
Kister and Schmidt[12] describe an organism closely resembling _B.
pestis_ in many respects, and with which guinea pigs could be
successfully infected by the cutaneous method. This organism, which was
also pathogenic for rats and mice, belongs to the hemorrhagic septicæmic
group. It differed from _B. pestis_ in that it gave no involution forms
when grown upon salt agar and was much more rapidly fatal to laboratory
animals.
Augeszky[13] observed an epidemic among gray rats in his laboratory
which was due to a pest-like organism belonging to the Friedlander
group. The animals died after a couple of days of illness. At the
post-mortem examination the spleen was found large, soft, and congested.
There was a hyperæmia of the intestines, lungs, and liver. In the spleen
were found many, and in the heart’s blood few, capsulated bacilli, some
of which resembled _B. pestis_. The cultural reactions were in nowise
similar to those of _B. pestis_. He found that inoculation of rats with
a pure culture of this organism sometimes killed in as short a time as
twenty-four hours, sometimes as late as two or three weeks, and in some
cases the lesions were not very unlike those sometimes produced by _B.
pestis_. However, this organism by its different cultural reactions, and
the fact that the capsule is usually easily demonstrated, would probably
never be a source of any confusion.
ARTIFICIAL INFECTION OF RATS WITH PLAGUE.
For laboratory purposes in general it is customary to use tame white
rats, and in plague work they are especially satisfactory, as they are
easily handled, rarely harbor fleas, are very susceptible to the
infection, and finally and most important, they frequently die a day or
two earlier than guinea pigs. At times it may be necessary to use wild
rats on account of a failure in the supply of white rats, or for the
sake of economy. This may be done very satisfactorily, if one bears in
mind the fact that a considerable number of wild rats are more or less
immune to plague infection, especially when the infectious material is
introduced by Kölle’s (cutaneous) method. Therefore, it is always
advisable to use three or four wild rats where one white rat would be
sufficient. They should be kept in a container of such design that there
is no possibility of their escaping. The inoculation is best conducted
with the animal under the influence of ether.
MODES OF INFECTION.
Rats may be infected experimentally by the ingestion of contaminated
material, and by the application of virulent plague bacilli to a mucous
or a cutaneous surface, or by subcutaneous injection of the organism.
Practically we may confine our study to inoculation by the cutaneous
method, and to subcutaneous inoculation, when the material is injected
in the ordinary manner. A useful modification of the latter method is to
make a small pocket under the skin of the abdomen and thrust the
suspected material into this pocket. This avoids the necessity of making
an emulsion of infectious matter, such as the organs of an animal. The
time that elapses between the inoculation of a rat with virulent culture
of plague bacilli and its death varies somewhat with the size of the
dose and with the mode of inoculation. The following table, compiled
from work in San Francisco, shows the day of death of a few white rats
and a considerable number of wild rats using the strain of _B. pestis_
that was found in the recent epidemic here. Some were inoculated by the
cutaneous and some by the subcutaneous method:
───────────────────────────────────┬─────────────────┬─────────────────
Day of death. │ White rats. │ Wild rats.
───────────────────────────────────┼─────────────────┼─────────────────
Second │ │ 3
Third │ 5│ 27
Fourth │ 7│ 41
Fifth │ 1│ 30
Sixth │ 1│ 9
Seventh │ │ 8
───────────────────────────────────┼─────────────────┼─────────────────
Total │ 14│ 118
───────────────────────────────────┴─────────────────┴─────────────────
The wild rats were all _Mus norvegicus_.
The _lesions_ found, when an artificially inoculated rat is examined
after death, are in a general way similar to those found in naturally
infected rats with certain differences to be mentioned later.
In order to obtain accurate figures as to the frequency of the various
lesions in inoculated rats, I have compiled the data from the records of
the federal laboratory in San Francisco of a considerable number of wild
rats that have been inoculated in the course of various investigations
and have died of acute plague. The rats were practically all of the
species _Mus norvegicus_.
_Artificially inoculated (subcutaneously) plague rats._
──────────────┬─────────┬────────────┬─────┬────────┬────────┬─────────
│ Local│Subcutaneous│Bubo.│Granular│Enlarged│ Pleural
│reaction.│ injection.│ │ liver.│ dark│effusion.
│ │ │ │ │ spleen.│
──────────────┼─────────┼────────────┼─────┼────────┼────────┼─────────
Present │ 36│ 48│ 19│ 47│ 56│ 18
Very extensive│ 1│ [Q]2│ │ │ │ 8
Slight │ 2│ 6│ │ │ │ 8
──────────────┼─────────┼────────────┼─────┼────────┼────────┼─────────
Total present │ 39│ 56│ 19│ 47│ 56│ 34
Absent │ 10│ 4│ 39│ 15│ 3│ 21
Not recorded │ 13│ 2│ 4│ │ 3│ 7
──────────────┼─────────┼────────────┼─────┼────────┼────────┼─────────
Total │ 62│ 62│ 62│ 62│ 62│ 62
──────────────┴─────────┴────────────┴─────┴────────┴────────┴─────────
Footnote Q:
Intense.
All of the lesions aside from the local reaction were present and well
marked in six cases.
_Artificially inoculated (cutaneously) plague rats._
──────────────┬─────────┬────────────┬─────┬────────┬────────┬─────────
│ Local│Subcutaneous│Bubo.│Granular│Enlarged│ Pleural
│reaction.│ injection.│ │ liver.│ dark│effusion.
│ │ │ │ │ spleen.│
──────────────┼─────────┼────────────┼─────┼────────┼────────┼─────────
Present │ 16│ 34│ 42│ 58│ 58│ 22
Very extensive│ 1│ [R]15│ │ │ │ 6
Slight │ 6│ 13│ │ │ │
──────────────┼─────────┼────────────┼─────┼────────┼────────┼─────────
Total present │ 23│ 62│ 42│ 58│ 58│ 28
Absent │ 37│ 6│ 26│ 11│ 8│ 37
Not recorded │ 9│ 1│ 1│ │ 3│ 4
──────────────┼─────────┼────────────┼─────┼────────┼────────┼─────────
Total │ 69│ 69│ 69│ 69│ 69│ 69
──────────────┴─────────┴────────────┴─────┴────────┴────────┴─────────
Footnote R:
Intense.
All of the lesions aside from the local reaction were present and well
marked in five cases.
LOCAL REACTION.
The most striking difference between natural and artificial plague in
rats is the presence of a reaction at the site of inoculation in the
majority of cases where the organism is introduced subcutaneously, and
in about a third of the cases where the infectious material is rubbed on
the shaven skin (cutaneous inoculation). The local reaction may exist
only as a yellowish-brown crust, overlying a granulating surface, and
associated with a trifling thickening of the skin and subcutaneous
tissue. It may appear as one or more firm papules 3 or 4 millimeters in
diameter. The most frequent appearance is a brawny œdematous and
blood-stained reaction which extends over an area perhaps an inch in
diameter; at times purulent change may be well advanced. Very rarely one
finds so extensive an œdema as to cause the lesion to somewhat resemble
the widespread gelatinous reaction seen so commonly in the guinea pig.
On one or two occasions we have seen an extensive slough at the site of
inoculation.
BUBO.
It is very exceptional that one finds in cases of induced plague the
typical, firm, caseous bubo surrounded by an infiltrated area, as is so
commonly seen in natural infection in rats. The glands are sometimes
enlarged and injected without other changes. The commonest lesion,
however, is a markedly enlarged gland which upon close inspection is
seen to have a number of yellowish points just under the capsule. These
points are especially well seen when a section is made through the
gland. The gland may be squeezed out of the capsule and it breaks down
readily enough when pressure is made upon it; but the uniform necrotic
process that one sees so often in natural rat plague is absent.
LIVER.
Granular lesions precisely like those found in natural infections are
very common. If the rat has died on the sixth day or later, the ordinary
lesions are apt to be replaced by necrotic foci that may be as much as 2
millimeters in diameter.
SPLEEN.
This organ is found mottled more frequently than in natural plague
infection, and large granules are much more common.
The subcutaneous injection is rarely so well marked as it is in natural
infections.
Pleural effusion of the same nature as that found in natural plague is
common. Hemorrhagic foci are not rare in the lungs, and occasionally the
organs are partly consolidated.
CHRONIC PLAGUE DUE TO ARTIFICIAL INOCULATION.
Occasionally a rat that has been inoculated but has survived a week or
longer, will show, when killed, only an abscess at the site of the
injection. Stained smear preparations may show a large variety of
bacterial forms. We have not been able to demonstrate the presence of
_B. pestis_ in these lesions, yet there is no doubt but that the lesion
is the result of the inoculation.
A lesion more frequently found is a caseous or a purulent lymphatic
gland. If the inoculated rat has been killed about ten days after the
inoculation, in some cases one or more of the peripheral lymph glands
will be found to be surrounded by an infiltration, and the gland itself
will be purulent or less frequently caseous. Such lesions are
occasionally met with in rats in which there is no suspicion of plague
infection; but they are seen so frequently among rats that have survived
artificial inoculation with _B. pestis_, there is no doubt but that in
these cases they are the result of the inoculation. In several such
cases pest-like organisms have been demonstrated in smears, and acute
plague has been produced in guinea pigs by inoculation with the pus
found in these lesions. Not infrequently in these cases the spleen will
be found enlarged and looking very much like the organ in acute plague,
but cultures from this organ in such cases have in my experience
remained sterile.
In other cases the only lesions will be found in the spleen. The organ
is enlarged and contains a number of caseous nodules. These nodules vary
in number from four or five to thirty or forty and in size from the head
of a pin to a lesion 0.3 centimeter in diameter. In a number of such
cases the nature of the lesion has been demonstrated by animal
inoculation. For example, in a series of experiments carried out to
determine the susceptibility of San Francisco rats to plague infection a
large _Mus rattus_ died on the eleventh day after inoculation. The
post-mortem examination showed nothing except an enlarged spleen which
contained about a dozen caseous nodules, the largest of which was not
over 2 millimeters in diameter. The nodules were very firm and the
capsule smooth, so that they were held with difficulty with dressing
forceps. Cultures from the liver and the spleen remained sterile, but a
piece of the spleen was placed beneath the skin of a guinea pig. This
animal died of acute plague, and a pure culture of _B. pestis_ was
isolated from its liver. In some of these cases the liver will show
large, distinct, whitish caseous foci. In another case a small _Mus
norvegicus_ was killed on the twelfth day after a cutaneous inoculation
from an artificially infected squirrel. No lesion was found except in
the spleen which was not materially enlarged, but which presented two
small whitish caseous granules on the surface, neither being over 1
millimeter in diameter. A piece of the spleen containing one of these
granules was put under the skin of the belly of a guinea pig. The guinea
pig died on the fourth day with the usual lesions of acute plague.
Occasionally in these cases of chronic plague punctate hemorrhages or
even areas of consolidation are found in the lungs.
THE HISTOLOGY OF RAT PLAGUE.
The most recent and satisfactory work on this subject is that of
Ledingham [14], who has studied the lesions of both natural and induced
plague in rats. The following is a very brief abstract of his work. The
reader is referred to the original for a full study of the subject.
NATURAL RAT PLAGUE.
Two groups of cases are distinguished, first, those in which a large
number of _B. pestis_ are found in the liver and in the spleen. In the
spleen this is accompanied by hemorrhages and congestion of the pulp
sinuses and in the liver with congestion of the capillaries. These are
early cases.
In the second group, or the later cases, there are extensive reaction
changes in the tissues. In the spleen this leads at times to distinct
abscess formation, but more frequently to a walling off of the foci of
necrosis. In the liver more or less focal necrosis is found; sometimes
the areas of “necrosis” may be so extensive that little healthy liver
tissue remains. Bacilli are usually to be demonstrated in these areas of
necrosis. Giant cells of the Langhans type may be found in the
neighborhood of these foci.
The granular appearance of the liver is attributed to “hemorrhages and
the focal necroses, together with the fatty changes in the liver cells.
It must be understood, however, that a peculiar honeycomb-like vacuolar
degeneration of the liver cell protoplasm was far more frequent than any
actual, coarse, fatty infiltration. The granular appearance of the
spleen is due partly to endothelial catarrh and partly to subcapsular
changes.”
In experimental rat plague Ledingham found the lesions to resemble those
of the first group of cases referred to above. There is usually marked
bacteraemia; focal necroses of the liver are scanty.
In a chronic case, minute abscesses were found scattered through the
spleen. In the center of the abscesses were found clumps of degenerated
bacilli. The areas were walled off by epithelioid and spindle cells and
numerous giant cells of the tubercular type.
IMMUNITY OF RATS.
Contrary to the general impression the wild rat is not an animal
especially susceptible to plague infection. The Indian Plague Commission
[19] found that when rats are inoculated by the cutaneous method from
the spleen of infected rats 59 per cent are immune to infection. A
series of experiments conducted in the federal laboratory in San
Francisco showed that when inoculated with highly virulent cultures of
_B. pestis_ there is an immunity which is, however, more frequent among
the large rats. When inoculated cutaneously with tissue containing large
numbers of _B. pestis_ from plague infected human beings, rats, or
squirrels, about 15 per cent of small rats and about 50 per cent of
large ones were found to be immune. There is no good reason for
believing that this immunity of San Francisco rats was due to a previous
attack of the disease. Indeed, it was known beyond a doubt that some of
the immune rats had never had an opportunity of becoming infected with
plague in nature and thereby establishing an acquired immunity. We may
mention here the fact that has been observed by many workers, and which
we have amply confirmed, that rats are readily immunized by antiplague
serum.
The subject of the transfer of infection directly from rat to rat by
cutaneous or subcutaneous inoculation through a series of the animals is
one that is evidently intimately associated with the preceding subject,
as it is quite evident that an immune rat or several of them might
terminate a series without any actual diminution in the virulence of the
organism transferred. It is quite plain that the success of such an
experiment would depend largely upon the number of rats used in each
transfer. The Indian Plague Commission [19] had no difficulty in
carrying infection through twenty-six transfers, using from six to fifty
rats in each transfer.
Pound [7] in a series of eight experiments, was never able to convey the
infection successfully beyond the sixth rat, using but one rat for each
transfer. There was no apparent lessening of the virulence of the
organism and each series appears to have been terminated abruptly by
encountering an immune rat.
Baxter-Tyrie [15] says:
It is probable that under certain natural circumstances a reduction in
the virulence of the organism is effected and a comparative immunity
is conferred on the rats. The infection of immigrant rats is, however,
severe, and their arrival is heralded by a heavy mortality. In the
same manner an infected rat imported into a fresh locality produces a
similar result. This attenuation of virulence is responsible for the
condition known as chronic rat plague.
Several experiments conducted in San Francisco to determine this point
have given results that I regard as showing merely the presence of a
considerable percentage of immunity among the rats. It was observed that
in each case certain of the rats died of acute plague even in the last
transfer. It was very evident that had certain combinations of immune
rats been encountered the experiment might have terminated at any point.
On the other hand, by being especially fortunate in using nonimmune
rats, the experiments might have given a much higher percentage of cases
of acute plague. Unfortunately it was necessary to terminate these
experiments in each instance before they could be regarded as completed.
The reason for the natural subsidence of plague among rats in any
community is a point about which much more evidence must be obtained
before we can speak with any degree of certainty. It may be due to the
lack of susceptible material, possibly to a loss of virulence of the
organism; but it seems more probable that it is due to a change in the
number or relations of the ectoparasites of the rat.
Adequate measures of rat extermination, while they may never bring about
the ideal condition of a community that is free from rats, are, as is
shown by the recent experience in San Francisco, of the utmost value in
shortening the epizootic.
REFERENCES.
Endnote 1:
Skschivan (Centralblatt für Bacter., etc., 1903, Vol. XXXIII, No. 4,
p. 260).
Endnote 2:
Kister & Schumacher (Zeit. für Hyg. u. inf. Krank., Vol. LI, 1905).
Endnote 3:
Indian Plague Commission (Journal of Hygiene, 1907, Vol. VII, No. 3).
Endnote 4:
White (Medical Record, vol. 67, No. 4, Jan. 28, 1905).
Endnote 5:
Kitasato (Philippine Journal of Science, Vol. I, No. 5, 1906).
Endnote 6:
Wherry, Walker & Howell (Journal Am. Med. Assn., April 11, 1908, Vol.
L, No. 15).
Endnote 7:
Pound (1907, Report on Plague in Queensland, B. B. Ham, p. 134).
Endnote 8:
Dunbar & Kister (1904, Centralblatt für Bact., etc., Vol. XXXVI, No.
1, p. 127).
Endnote 9:
Kolle & Martini (Deut. Med. Woch., Jan. 2, 1902, Vol. XXVIII).
Endnote 10:
Kister (Centralblatt für Bact., etc., July 24, 1906, Vol. XLI, No. 7).
Endnote 11:
Neumans (1903, Zeit. f. Hyg. u. inf. Krank., Vol. XLV, No. 3, p. 451).
Endnote 12:
Kister & Schmidt (1904, Centralblatt für Bact., etc., Vol. XXXVI, No.
3, p. 454).
Endnote 13:
Aujeszky (1904, Centralblatt für Bact., etc., Vol. XXXVI, No. 5, p.
603).
Endnote 14:
Ledingham (Journal of Hygiene, 1907, Vol. VII, No. 3).
Endnote 15:
Baxter-Tyrie (Journ. of Hygiene, Vol. V, 1905, p. 315).
Endnote 16:
Wherry (The Journal of Infect. Diseases, Dec. 18, 1908, Vol. V, No.
5).
Endnote 17:
Klein (The Bacteriology and Etiology of Oriental Plague, MacMillan and
Co., London, 1906).
Endnote 18:
Indian Plague Commission (Journal of Hygiene, 1907, Vol. VII, No. 6,
p. 761).
Endnote 19:
Indian Plague Commission (Journal of Hygiene, 1906, Vol. VI, No. 4).
RAT RECORD CARD.
[Legend: O = Ordinary; W = White belly; R = Red; Go. = Gopher rat; S =
Small; M = Medium; L = Large; M. R. = Mus rattus; M. N. = Mus
norvegicus.]
───┬────────┬───────────────┬─────┬────────┬────────────┬─────┬─────────
No.│ Date. │District No. 6.│Sex. │ Size. │ M. N. │M. R.│Pregnant.
───┼────────┼───────────────┼──┬──┼──┬──┬──┼──┬──┬──┬───┼──┬──┼─────────
„ │ „ │ „ │M.│F.│S.│M.│L.│O.│W.│R.│Go.│O.│W.│ „
───┼────────┼───────────────┼──┼──┼──┼──┼──┼──┼──┼──┼───┼──┼──┼─────────
19 │Dec. 10,│ 401 Fillmore │1 │ │ │1 │ │ │ │1 │ │ │ │
│ 1908 │ street │ │ │ │ │ │ │ │ │ │ │ │
20 │ do │ do │ │1 │ │ │1 │1 │ │ │ │ │ │ [S]7
───┴────────┴───────────────┴──┴──┴──┴──┴──┴──┴──┴──┴───┴──┴──┴─────────
Footnote S:
Number of fœtuses.
PLAGUE RAT CARD.
PLAGUE RAT NO. 50.
Date: June 20, 1908.
Species: _M. norvegicus_.
From District No. 6, sewer, Haight and Steiner Streets.
Condition: Badly injured by trap; thorax crushed.
Subcutaneous injection: General, marked.
Lymphatic glands, bubo or other lesions: Right inguinal bubo, caseous.
Liver: Typical whitish granules.
Spleen: Large, dark, firm.
Pleural effusion: Unable to say.
Purulent or caseous foci:
Diagnosis from gross lesions: Plague.
Diagnosis from smears: Plague (spleen and bubo).
Cultures: _B. pestis_ recovered from liver culture.
Inoculation, guinea pig No. 50 A, +6.25.08.
Vaccination, guinea pig No. 50 B, +6.26.08.
Date suspicious:
Date positive: June 20, 1908.
Date negative:
[Illustration:
A HOEN & CO BALTIMORE.
NECROPSY APPEARANCE OF PLAGUE-INFECTED RAT
]
[Illustration:
A HOEN & CO BALTIMORE
NECROPSY APPEARANCE OF NORMAL RAT
]
RAT LEPROSY.
By WALTER R. BRINCKERHOFF, S. B., M. D.,
_Assistant Director Leprosy Investigation Station, United States Public
Health and
Marine-Hospital Service, Honolulu, Hawaii_.
INTRODUCTION.
The leprosy-like disease of the rat is of great interest to leprologists
because of its close similarity to the disease leprosy in man. Its
practical importance to those engaged in the study of the human disease
is increased by the fact that it can be artificially propagated under
laboratory conditions from animal to animal and, still more important,
can be transferred from the species in which it occurs naturally (_Mus
norvegicus_) to a more tractable laboratory animal (_Mus albus_). The
brief description of the affection which follows is intended to assist
in its recognition and to stimulate the interest of investigators in the
disease, which presents problems replete with interest to the study of
pathology or bacteriology and of great promise to those engaged in the
investigation of human leprosy. It is earnestly hoped that the
investigation of this disease will be undertaken in general medical
research laboratories, as it is extremely probable that certain of the
most difficult problems presented by leprosy in man can be studied in
this disease of the rat, and if solved there the information gained can
be directly applied to the solution of the analogous problems in the
human disease.
REVIEW OF LITERATURE.
The first publication on rat leprosy was made by Stefansky (1903), who
observed the disease in Odessa during an antiplague campaign against
rats.
Rabinowitch (1903) found the disease among rats in Berlin and confirmed
the work of Stefansky.
Dean (1903) discovered the disease independently in London, and in a
later publication (1905) reports success in transferring the disease by
artificial inoculation.
Tidswell (1906) reports a case of the disease in a rat caught in Sydney,
New South Wales, Australia.
The English Plague Commission observed the disease in India in 1907
(Wherry).
Wherry (1908) and McCoy (1908) report upon the finding of the disease in
rats caught in San Francisco, Cal.
Mezincescu (1908) has studied the disease and attempted to determine its
relationship to known human lepra by complement fixation tests.
DESCRIPTION OF DISEASE.
_Geographical occurrence._—It would be premature at present to make
didactic statements as to the geographical distribution of the disease,
for its discovery has usually depended upon antiplague measures, which
are not world-wide in their scope. In spite of this it seems profitable
to briefly review the known occurrence of the disease in relation to
that of human leprosy. When such a comparison is made we note that the
disease is present among the rats of Berlin, a city which is practically
free from human lepra. On the other hand in Honolulu, which is an
endemic focus of human leprosy, in the examination of 16,000 rats,
during an antiplague campaign, no case of rat leprosy was encountered.
In addition to the scrutiny of the rats examined for plague in Honolulu,
an attempt was made to obtain leper rats by offering a reward for a rat,
dead or alive, infected with the disease. This offer was given wide
publicity in the Territory, but brought no results.
_Occurrence of the disease._—The proportion of rats infected with the
disease in different localities varies greatly, as will be seen in the
following table:
TABLE 1.—_Proportion of leper rats to the total rats examined._
───────────────────────────┬───────────────────────────┬───────────────
Place. │ Observer. │ Proportion.
───────────────────────────┼───────────────────────────┼───────────────
│ │ _Per cent._
Odessa │Stefansky [301] │ 4–5.000
Sydney │Tidswell [305] │ .001
San Francisco │Wherry [308] │ .210
Do │McCoy [310] │ .160
Honolulu │Currie[T] │ .000
───────────────────────────┴───────────────────────────┴───────────────
Footnote T:
Personal communication.
Rats in the late stage of the disease are easily recognized by the
presence of a patchy alopecia associated with cutaneous and subcutaneous
nodules, which may or may not be the site of open ulcers. The diagnosis
can be readily confirmed by a microscopic examination of a smear from an
ulcer or a nodule, which will show the specific bacillus of the disease
in enormous numbers.
Stefansky[301] describes two clinical types of the disease, the one
localized particularly in the lymph nodes, the other in the skin and
muscles. The glandular type was the more common. Dean[304] thinks that
no line of demarcation can be drawn between these clinical types.
Dean[304] and Wherry[307] both mention that attention was attracted to
the diseased animals by the fact that they were seen abroad during
daylight in an obviously sick condition.
The skin, in a well-developed case of the disease, presents a patchy
alopecia coincident with thickening and nodule formation, which is
situated in the subcutaneous tissue. The cut surface of the nodules or
thickenings is light yellow in color, is clean, dry, and cheese-like. In
the region of the nodules the skin is atrophic, and ulcers often form on
the prominent parts of the affected area. The subcutaneous fat tissue is
diminished in amount. Histologically the process is seen to be
practically confined to the subcutaneous tissue and to consist
essentially in the presence of cells rich in protoplasm, with vesicular
nuclei, whose cell body is more or less completely filled with slender
acid-fast bacilli. The subcutaneous fat is replaced by such a tissue.
All investigators who have studied the disease agree in emphasizing the
similarity of the histology of the lesion to that in leprosy in man.
When the musculature is involved the muscle fibers atrophy and the
fibers are infiltrated with the specific bacilli. The affected muscle is
friable, and macroscopically grayish white in color.
The peripheral lymph nodes are commonly involved, though McCoy[310]
reports a case in which only the pelvic and mesenteric nodes were
diseased, and in the Tidswell case[305] the peripheral nodes were not
enlarged. The typically affected nodes are enlarged, sometimes measuring
as much as 3 centimeters in the greatest extent, firm, and, on section,
opaque pale yellow-white in color. In the experimental disease the
writer has frequently found the characteristic bacilli of the disease in
peripheral lymph nodes which were very slightly enlarged and presented
no macroscopic lesion. Dean[304] has observed invasion of the
submaxillary or salivary glands by extension from infected cervical
lymph nodes. Wherry[308] notes that in his cases he did not find the
submaxillary or cervical glands involved, which fact he contrasts with
two early cases in which the skin and adjacent axillary or inguinal
nodes were involved.
Microscopically the lymph nodes show large numbers of cells in the
sinuses similar to those in the skin lesions. Multinuclear giant cells
are frequently observed which may measure as much as 70 to 80
microns[304]. The protoplasm of the cells is loaded with the specific
bacilli of the disease. The lymph follicles, trabeculæ, and capsule of
the glands are also invaded by the bacilli.
The internal organs are relatively slightly affected in the natural
disease. Small foci have been found in the liver by Dean[304] and in the
liver and spleen by McCoy[310]. Wherry[307] reports finding the bacilli
in smears from both the liver and spleen. The writer has found
microscopic lesions containing the characteristic bacilli in the liver
in a case of the experimental disease.
Lesions have been observed in the bone marrow by Dean[304], and the same
author states that the nerves are invaded by the bacilli of the disease.
McCoy[310] found the bacilli in the urinary bladder in one case.
With a disease showing such a striking similarity to human leprosy,
attention has naturally been directed to the bacteriological examination
of the nasal mucus. Dean[304] and Wherry[307] have both found the
characteristic bacilli in the nasal mucus, while McCoy[310] has failed
to do so. The writer’s experience has been confined to the experimental
disease, and in his animals the nasal examinations have been negative.
ETIOLOGY.
The accepted etiological factor in the disease is an acid-fast bacillus
3 to 5 microns in length and 0.5 micron wide. The bacilli resemble very
closely the lepra bacillus of man, but seem to have somewhat greater
power to hold carbol-fuchsin stain against mineral acids. The bacilli
often have rounded ends and may be curved. The beaded appearance so
often seen in lepra bacilli is common. The bacilli show the same
tendency to form bundles that is such a marked characteristic of
_Bacillus lepræ_. To one familiar with the microscopic appearance of
smears from the discharges and lesions of human leprosy the picture
presented by similar preparations from the disease of the rat is most
striking.
The organism does not grow on the usual culture media—Stefansky [301],
Rabinowitch[302], Dean[304], Tidswell[305]—or on certain special
media—Dean[304].
The organism is not pathogenic for the guinea pigs—Dean[304],
Tidswell[305]—rabbit, mouse, monkey—Dean[304]. The disease can be
transmitted to black and white rats—Dean[304], Wherry.
SUMMARY.
In the leprosy-like disease of rats we have an affection which closely
resembles, both in its etiological factor and in its pathology, the
disease leprosy in man. The fact that the disease is readily propagated
in a laboratory animal permits of its investigation in any laboratory.
It is earnestly hoped that the study of this disease will be taken up by
bacteriologists and pathologists, as in this way valuable information
may be gained which will be applicable to the problems presented by
leprosy in man.
BIBLIOGRAPHY.
Endnote 301:
Stefansky, W. K., ’03. Eine lepraähnliche Erkrankung bei Wanderratten.
Cent. f. Bact., Bd. 33, Orig. S. 481. Baum. Jahres., Bd. 19, S. 496.
Endnote 302:
Rabinowitch, L., ’03. Ueber eine Hauterkrankung der Ratten. Cent. f.
Bact., Bd. 33, Orig. S. 577. Baum. Jahres., Bd. 19, S. 496.
Endnote 303:
Dean, G., ’03. A Disease of Rats caused by an acid-fast Bacillus.
Cent. f. Bact., Orig. Bd. 34, S. 222. Baum. Jahres., Bd. 19, S. 494.
Endnote 304:
Dean, G., ’05. Further Observations on a Leprosy-like Disease of the
Rat. Jour. Hyg., vol. 5, p. 99.
Endnote 305:
Tidswell, F., ’06. Note of Leprosy-like Disease of Rats. Lepra, vol.
6, p. 197.
Endnote 306:
English Plague Commission. Jour. Hyg., vol. 7, p. 337. Cited by
Wherry.
Endnote 307:
Wherry, W. B., ’08. The Leprosy-like Disease among Rats on the Pacific
Coast. Jour. Am. Med. Asso., vol. 50, No. 23. Cent. f. Bact., Ref. Bd.
42, S. 664.
Endnote 308:
Wherry, W. B., ’08. Notes on Rat Leprosy and on the Fate of Human and
Rat Lepra Bacilli in Flies. Public Health Reports, U. S. P. H. and M.
H. S., vol. 23, p. 1841. Jour. Infec. Dis., vol. 5, p. 507.
Endnote 309:
Mezincescu, D., ’08. Maladie Lépreuse des Rats et ses Relations avec
la Lèpre Humaine. Compt. Rend. Soc. Biol., T. 64, p. 514. Cent. f.
Bact., Ref. Bd. 42, p. 664.
Endnote 310:
McCoy, G. W., ’08. Rat Leprosy. Public Health Reports, U. S. P. H. and
M. H. S., vol. 23, p. 981. Jour. Am. Med. Asso., vol. 51, p. 690.
The writer wishes to express his gratitude to Dr. George Dean for
histological material from the natural and experimental disease, and to
Doctors Wherry and McCoy for rats inoculated with the disease and normal
animals for its propagation.
BACTERIAL DISEASES OF THE RAT, OTHER THAN PLAGUE AND RAT LEPROSY.
By DONALD H. CURRIE,
_Passed Assistant Surgeon, United States Public Health and
Marine-Hospital Service_.
So far as is known, the several species of rats that are found about the
habitations of man—_Mus norvegicus_, _Mus rattus_, _Mus alexandrinus_,
and _Mus musculus_—are naturally subject to but few bacterial diseases
as compared to some other animals. Interest in this matter has only
recently been aroused, owing to the rôle played by the rat in the spread
of bubonic plague. When we consider the immense number of rats that have
been examined in connection with antiplague work by trained
investigators in recent years, and that to many investigators the
thought must have come that the discovery of some rat destroying
bacterium would be of the greatest utility, it appears more than
probable that few such natural diseases exist.
Plague is the one natural bacterial disease that has demonstrated its
power to destroy these rodents in numbers sufficiently large to attract
general attention; scientific investigation has only been able to add a
few other bacterial diseases, and these are probably for the most part
rare ones, causing the death of a very small percentage of the total rat
population.
Of the “natural” diseases (i. e., spontaneous, in distinction to
diseases that can only be produced artificially, under laboratory
conditions) the following are the more important ones:
Rat plague and rat leprosy, which are made the subject of special
chapters in this publication, must be mentioned as the most important
diseases observed among rat populations.
DANYSZ’S BACILLUS OR BACILLUS TYPHI MURIUM OF LOEFFLER.
These are probably identical organisms, differing only in their degree
of virulence, at least their pathogenicity alone distinguishes them in
the laboratory. They are both members of the paracolon group. They
produce a diffuse cloudiness in broth, ferment glucose but not lactose
or saccharose, do not liquefy gelatin nor coagulate milk.
_B. typhi murium_ (Loeffler) is fatal to mice (_Mus musculus_), but not
to rats. M. Danysz isolated a bacillus during an epidemic of field mice
which was indistinguishable from the above, except that its virulence
was capable of being raised to a point where it would destroy a
relatively large percentage of rats inoculated with it by feeding. We
see from this that, strictly speaking, it is not a natural disease among
rats, still there are cases where its virulence has for a time remained
high enough to infect a considerable per cent of rats exposed to those
that have sickened of it. Not only is this true in cage experiments, but
probably it sometimes occurs in nature after the virus is once
thoroughly introduced (an article by M. Danysz; also experience of this
service in plague in San Francisco, 1903 to 1905), and may therefore be
grouped under the list of “natural” infections. This bacillus is
unfortunately of a very unstable nature, in so far as its virulence is
concerned; some cultures appearing to be avirulent, while others cause
an all but absolute mortality among the rodents eating it.
The duration of the disease is variable and appears to depend somewhat
on the size of the dose received, as well as virulence of the culture.
We have seen death in thirty-six hours or less following ingestion. On
the other hand, it may occur in two weeks. Usually it occurs in from six
to twelve days. In a typical case when the animal has lived ten or
twelve days it is much emaciated, its tissues are dry, and intestinal
hemorrhages are sometimes met with. When the disease is much prolonged a
pustular eruption may be present over the skin. The organism can often
be isolated from the heart blood by plating, such isolation alone
affording means of diagnosis. The only present interest this organism
has is as a means of destroying the rat. It was believed to be harmless
to man, but more recently cases of human illness have been reported that
were believed to have been caused by infection with this bacillus.
PNEUMONIA.
We have recently seen a case of lobar pneumonia in a rat in which a
diplococcus was present in pure culture. Possibly connected with this is
a condition of abscess of lung, which is not very uncommon. The cavity
is filled with a creamy or cheesy matter composed of broken-down cells.
Often these cavities break into the pleura. Several morphological types
of organisms are found, but from their variation this laboratory has
regarded them as secondary or accidental, especially as we have failed
to demonstrate that this material was infectious.
STAPHLOCOCCUS ABSCESSES.
These are rather common and may occur subcutaneously or in the
superficial muscles of any part of the body.
BACILLUS PSEUDO-TUBERCULOSIS RODENTIUM (PFEIFFER).
This organism that infects rats is of interest from its close
resemblance to the plague bacillus. It is difficult to distinguish the
two organisms by ordinary cultural or animal tests. The earlier writers
claimed that _B. pseudo-tuberculosis rodentium_ could be differentiated
by its power of coagulating milk, but more recently this difference has
been found to be an inconstant one.
TOYAMA’S BACILLUS.
Toyama has described an organism which he states is pathogenic for _Mus
rattus_, field and house mice (_Mus musculus_), but not pathogenic for
_Mus norvegicus_.
It causes congestion of lungs, enlargement of lymph nodes, especially in
the neck, and enlargement of the spleen. It was isolated from a natural
epizootic among _Mus rattus_. It is a nonspore-bearing bacillus, without
capsule, stains without showing bipolarity, and grows upon ordinary
media.
Among other bacteria that have been described as causing diseases in
rats may be mentioned:
_Von Schilling’s bacillus_, allied to Danysz’s organism.
_Bacillus “Eris,”_ a member of the colon group.
_Bacillus muris_, a member of the _B. diphtheria_ group.
Of the bacteria that show virulence for rats under laboratory
conditions, but, so far as is known, cause no spontaneous outbreaks, the
following are the best-known examples:
_Bacillus bovisepticus_ produces a fatal disease bacillus of swine
erysipelas (especially for albino rats), and the bacillus of tetanus.
Of the higher fungi (not strictly bacterial) we have:
_Streptothrix maduræ_ produces local swellings when inoculated
artificially.
It has been stated that rats occasionally suffer from a disease similar
or identical to the affliction in man known as favus (_Achorion
Schönleinii_).
INFECTIONS OF MICE (MUS MUSCULUS).
This species of _Mus_ is very susceptible to a large number of bacterial
diseases when inoculated under laboratory conditions. The following are
some of the best-known examples:
_B. murisepticus_, _Staphlococcus pyogenes_, _Streptococci_,
_Diplococcus pneumoniæ_, _B. pneumoniæ_ (Friedlander), Diplococcus of
pleuro-pneumonia of horses, _B. Typhi murium_, _B. anthracis_, B. of
malignant edema, _B. tetani_, _B. mallei_, _B. diphtheriæ vitulorum_,
_B. bovisepticus_, _B. suisepticus_, the bacillus of Mereshkowsky, and
many others. The last-named organism has been utilized to a limited
extent for the destruction of mice about dwellings.
ORGANIC DISEASES OF THE RAT, INCLUDING TUMORS.
By GEORGE W. MCCOY,
_Passed Assistant Surgeon, United States Public Health and
Marine-Hospital Service_.
The lesions described here are those that have been found in the routine
examination of rats for plague infection in the federal laboratory at
San Francisco during the past year, in which time approximately 120,000
rats have been examined.
As the subject had no special bearing upon the plague investigations,
but little time was spent in examining and recording the nature of
organic lesions that were observed. Notes, however, were made of many of
the conditions which were encountered, and these notes have been used as
the basis of this paper.
It is well known that various lower animals are subject to some of the
so-called organic diseases from which man suffers, and not a little
experimental work has been done in endeavoring to establish in animals
certain of the lesions commonly found in human pathology.
_Usefulness of wild rats for laboratory purposes._
We would call special attention to the fact that wild rats suffer
spontaneously from cirrhosis of the liver, fatty degeneration of the
liver, nephritis, and calculi of the urinary tract, and would,
therefore, probably furnish excellent subjects for the experimental
investigation of these diseases.
The objection may be made that the very fact that these animals do
suffer from these diseases spontaneously makes them unsuitable for
experimental purposes, as one could not be certain that any lesions
found were not spontaneously developed rather than that they were due to
the conditions imposed in an experiment. In reply to this objection we
would say that the most of these organic lesions occur so rarely in rats
in nature that one could almost ignore them.
The ease with which wild rats are obtained and the readiness with which
they adapt themselves to the conditions of life in captivity are factors
which should make them more extensively used for laboratory purposes
than is the case at present. We have described (New York Medical
Journal, Feb. 6, 1909) the methods that have been found useful in
keeping and handling these rodents. Without going into details here we
may say that if rats of approximately the same size are kept together in
a cage there will be practically no mortality from fighting. Of course,
there should be no overcrowding. Rats should be fed meat or cheese and
plenty of green food such as carrots or cabbage. In our experience in
San Francisco it has been found practicable to keep for a year one
series of ten inoculated wild rats without any loss. Judging from my
experience I have no hesitancy in saying that the natural mortality in
the laboratory is higher among both guinea pigs and white rats than it
is among wild rats.
It is almost certain that some of the lesions described below are due to
animal parasites, or to bacteria, but no such causative agent has been
identified.
CIRCULATORY APPARATUS.
We have seen no lesion of the circulatory system with the exception of a
few cases of pericardial effusion. The most extreme example was one in
which the pericardial sac was dilated to such an extent that it filled
almost the entire cavity of the thorax. The fluid in the sac was blood
stained and there were a number of recent adhesions between the visceral
and the parietal surfaces of the pericardium.
PULMONARY APPARATUS.
Pleural effusion, as is stated in another place, is an important sign of
plague infection. A clear, watery effusion has been found in a few cases
in rats that were not plague infected.
One example has come under observation of a large _Mus norvegicus_ that
had both pleural cavities almost entirely filled with a milky fluid. The
lungs were compressed and congested. Microscopical examination for
animal parasites and for bacteria was negative.
A condition of consolidation of the lungs which closely resembles the
stage of gray hepatization in lobar pneumonia in man is seen
occasionally. The area may involve half of a lung. Upon microscopical
examination one finds the air spaces and the small bronchi filled with
leucocytes. There was no cavity formation in any of the cases that have
come under observation.
Two relatively common purulent conditions of the lungs are encountered.
In the first of these, large and more or less distinctly loculated sacs
are found, which are filled with yellow semifluid caseous matter; in the
second, the lesion is of much the same nature, but the material in the
sac has the consistency of tough, ropy mucus. Aside from the main focus
of this sort, numerous smaller areas of the same nature are seen
scattered through the otherwise normal parts of the lungs. The extent of
some of these purulent processes is remarkable. We have seen cases in
which the chest cavity was almost filled by the lesions described.
DIGESTIVE TRACT.
CIRRHOSIS OF THE LIVER.
It was a matter of surprise to find well-marked cases of hepatic
cirrhosis in rats, as this disease in man has been pretty generally
regarded as very largely due to intemperance in the use of alcoholic
beverages. Such an etiology hardly accounts for the condition in the
rat. The lesion is by no means rare; well-marked cases are encountered
probably as often as once in a thousand rats. We have never seen it in a
young rat, probably because the condition develops slowly and the rat
reaches adult life before the process is complete. The organ is usually
somewhat yellowish, very firm, often, but not always, somewhat shrunken
in size. The surface of the whole organ is covered with small, rounded
elevations; a typical “hobnail-liver” in miniature.
Microscopically we find various degrees of increase of connective
tissue. In a well-marked case the capsule is much thickened, and heavy
bands of connective tissue run through the organ in every direction.
This increase of connective tissue is most marked in the vicinity of the
portal vein and its companion vessels. The microscope will show that in
some fields over half of the structure is made up of fibrous tissue. The
liver cells that remain appear to be normal. The presence of animal
parasites in the liver is frequently associated with a considerable
hypertrophy of the connective tissue of the organ. In a majority of
cases of hepatic cirrhosis, however, no parasites are to be found. One
case has come under observation in which the surface of the liver was
covered with a number of flattened, wart-like elevations. Upon section
nothing was to be found to account for this except an enormous
overgrowth of connective tissue.
FATTY DEGENERATION OF THE LIVER.
A considerable number of cases of well-marked fatty degeneration of the
liver have been seen. At times the fatty change is so extensive that the
organ floats when placed in water. Microscopically the liver cells are
found to be extensively infiltrated with fat granules.
HERNIÆ.
A few ventral herniæ have been observed. In the majority of the cases
the sac contained intestine only and this was easily reduced. On two
occasions other viscera have been found in the sac; the spleen on one
occasion and in another case along with several loops of intestine which
were easily reduced there was found the upper extremity of the right
division of the uterus which carried a cyst about 1 centimeter in
diameter. The cyst was partly adherent to the sac of the hernia. The
other division of the uterus was dilated and full of pus. The hernial
sac is rarely situated in the median line. One inguinal hernia has been
seen.
GENITO-URINARY TRACT.
NEPHRITIS.
Nephritis is a rather common condition in rats. Among the large (old)
ones it will be found probably once in every fifteen or twenty examined.
It has been found to be especially frequent in rats that are suffering
from the leprosy-like disease, as probably two-thirds of those having
that interesting infection will show marked evidence of nephritis. The
kidney is usually brownish or grayish, mottled, friable and often shows
cysts upon the surface and in the substance of the organ. Some of these
cysts may be as large as a pea, or indeed even much larger. The capsule
strips very readily.
Microscopically the lesions are found to be due partly to epithelial and
partly to interstitial change. There is a marked increase of connective
tissue rather irregularly distributed throughout the organ. The
epithelial cells show various degrees of degeneration; the nuclei are
stained very lightly, or not at all; granular change of the protoplasm
is well marked. Some tubules are encountered in which the epithelial
cells are entirely wanting.
Cyst formation is a conspicuous feature in many of the cases. These
cysts vary considerably in size, are often filled with granular débris,
and are more or less completely lined with epithelial cells which are
sometimes flattened. At times the epithelial lining is entirely wanting.
The glomeruli, on the whole, appear to be better preserved than are the
tubules. Occasionally areas are found in which there is a very marked
round cell infiltration between the epithelial structure. One of the
most marked cases of nephritis we have observed was in a large female
_Mus alexandrinus_, in which both kidneys were almost entirely replaced
by cystic formation, the largest cyst being perhaps 3 centimeters in
diameter by 4 centimeters in length, and full of a clear, watery fluid.
So extensive was the cystic formation that only a few remnants of kidney
tissue remained. Microscopical examination showed a marked increase in
the capsular and interstitial connective tissue, a shrinking of the
glomeruli, which were surrounded by well-marked fibrous capsules, and
extensive cyst formations. The lining of some of these cysts was made up
of epithelial cells. Others were quite bare. This rat had, in addition,
a large, rough calculus in the urinary bladder.
ABSCESS OF THE KIDNEY.
A female _Mus norvegicus_ had on one side of the neck a large cavity
full of caseous matter. In each kidney there were five or six
circumscribed collections of pus, the largest of which was about the
size of a pea. Microscopical sections through these abscesses showed
that they were walled off from the kidney structure proper by beginning
connective tissue formation. The abscess cavity was filled with
polynuclear leucocytes, some of them very markedly disintegrated. The
epithelial structure of the kidney proper showed some parenchymatous
degeneration.
ATROPHY OF A KIDNEY.
On one occasion we have seen a kidney represented by a very small
flattened mass of tissue, the nature of which was not quite clear until
microscopical examination showed a few fairly well-defined glomeruli and
a few cell groupings suggestive of tubules. Whether the condition was
congenital or acquired is not known. The other kidney appeared to be
normal in every respect. There was no evidence of compensatory
hypertrophy.
VESICAL CALCULI.
The bladder of rats very frequently contains very irregularly shaped,
rough, somewhat branching concretions. These concretions are rather soft
and tough and are dirty white in color.
In addition to these concretions we have seen several cases of
well-marked vesical calculi. In one case 21 smooth round stones which
completely filled the bladder were found. The total weight of the stones
was 3.8 grams. In another case 6 calculi were found, the total weight of
which was 7.8; the largest one weighing 5 grams. In a third case 8
smooth, round stones weighing 1.7 grams were found, the largest of which
weighed 0.6 gram. The last two cases were female rats; the sex of the
first was not recorded.
In each of these cases the bladder showed to the naked eye very marked
evidence of inflammation. The mucous membrane was reddened, villous, and
covered with tenacious mucus. In one case in which microscopical
examination was made the mucous membrane was found to be covered with
pus cells, the surface layers of which were undergoing degeneration.
Diseases of the genital tract in the human race analogous to those
mentioned below are so generally regarded as due for the most part to
infections from impure sexual relations that it was a distinct surprise
to find such lesions in rodents.
In the male abscesses are occasionally met with in connection with the
seminal vesicles. We have seen them varying in size from a pea to a sac
whose contents would have measured 3 or 4 cubic centimeters. In the
female purulent collections in the horns of the bifid uterus are
encountered, but they are rare. We have seen cases that were
anatomically exactly like the purulent lesions so commonly found in the
fallopian tubes of women. In one case one horn of the uterus was closed
at both ends and distended by a thin, watery pus into a large
sausage-shaped mass about the size of an index finger. The opposite horn
of the uterus contained six fœtuses. A very curious case was one in
which four fœtuses, each one a little less than an inch in length, were
found lying in the midst of a large, yellowish, puttylike mass that
distended one horn of the uterus into a balloon-shaped mass about 3
centimeters in diameter. The fœtuses were partly dried, and had
evidently been dead for a long time.
TUMORS.
Tumors among rats and mice are not infrequent when these animals are
kept in captivity, and the tumors of mice especially have been made the
subject of very extensive experiments for the purpose of determining the
mode of transmission, the question of immunity, and other subjects that
might throw light upon malignant growths in the human family. White or
tame rats have been much less used than mice. However, it is interesting
to note that the earliest observations on the successful transplantation
of a malignant growth from one animal to another was that of Hanau[101],
who reported a carcinoma of the external genitals of a white rat and he
succeeded in transplanting this tumor into other white rats.
I shall not make any attempt to review the enormous literature on tumors
in tame rats and mice, but shall merely mention some of the more
important points that have been learned in an experimental way in regard
to this subject. The histological nature of the tumors found in white
rats was of particular interest, as we wished to compare them with the
tumors that have come under observation among the wild rats in San
Francisco.
In addition to Hanau’s case of carcinoma cited above the following
tumors of white rats are mentioned. Herzog[102] observed a cystic
sarcoma of the neck of a white rat. Loeb[103] mentions three tumors of
white rats; an adenoma in the mammary gland, an adenocarcinoma of the
pancreas, and a carcinoma of the thyroid. Flexner and Jobling[104]
report a mixed cell sarcoma of the seminal vesicles of a white rat. This
tumor upon transplantation showed a marked tendency to produce
metastases. Gaylord and Clowes[105] report cases of fibrocarcinoma of
white rats arising apparently from infected cages, and they present
evidence that in certain breeding establishments carcinoma is endemic
among the white mice. Spontaneous tumors are much more frequently met
with in mice than in rats, and a number of epidemics of malignant
growths have been observed among mice in captivity.
Tyzzer[106] found in a mouse a primary adenocarcinoma of the lung and an
adenoma of the kidney. Loeb[107] found that upon the transplantation of
a pure gland-like tumor (carcinoma) which originated in the submaxillary
gland of a Japanese mouse both carcinoma and spindle cell sarcoma were
developed, and this observation, that transplanted tumors may give rise
to a different histological growth from that which was transplanted, has
been made by others. Tyzzer[108] reports 20 spontaneous tumors in mice.
Of these tumors 12 were papillary cyst-adenomas of the lung and were
mostly very minute, some of them microscopic; 2 were cyst-adenomas of
the kidney; 2 lymphosarcoma, 1 of the groin and 1 of the mediastinum,
and 4 were adenocarcinoma. These 20 spontaneous tumors occurred in 16
mice, 4 of them having tumors of 2 different types. Ehrlich and
Apolant[109] record the occurrence in a white mouse of a mixed tumor
(carcinoma sarcomatodes). Saul[110] mentions spontaneous papillary
adenocarcinoma and teleangiectatic carcinoma both in the mammary glands
of mice.
Saul showed that by planting the common liver worm of the rat
(_Cysticercus fasciolaris_) subcutaneously in a mouse he was able to
develop a tumor which partook of the nature of a malignant
(carcinomatous) growth. It will be seen by an examination of the data
presented below relating to spontaneous tumors in wild rats that a
considerable number of them have been associated with the presence of
the parasite Saul used in his experiments. He also states[111] that
Borrel found worms or their remnants in malignant tumors of mice.
When metastases occur in mouse tumors the most usual seat of the
secondary growths is in the lungs, thus Tyzzer[112] observed metastases
in 4 cases out of 73 mice inoculated with the Jensen tumor. He
demonstrated that the metastases took place by the blood vessels, not by
the lymphatic channels, although the tumors were of a carcinomatous
nature.
Simon[113], who reviews the subject of mouse tumors with special
reference to the subject of immunity, remarks that mouse carcinomata,
although found most frequently in old females, when transplanted grows
equally well in males, and better in young than in old animals. It has
been found by some observers that a rat or a mouse unsuccessfully
inoculated with a strain is thereafter immune, to even the most virulent
strain.
Haaland[114] and other writers have found a marked variation in the
susceptibility of different races of mice to mouse carcinoma.
Ehrlich[115] and his co-workers Apolant and Haaland have recorded many
experiments in transplantation of tumors of mice. They have demonstrated
that moderate heating of a mouse tumor lengthens the incubation period,
diminishes the number of successful transplantations, and brings about
certain changes in the histology of the tumors reproduced.
Gay[116] found a difference in the susceptibility of white rats from
different sources. In his work with carcinoma in rats he found
metastases regularly in the lungs and rarely in the lymph nodes. He was
able to raise the virulence of the tumor by transplantation of the lung
metastases. This increase of virulence was shown by increase in the
rapidity in growth, increase in metastases, and the increase of the
epithelial elements over the stroma.
Brooks[117] in considering the subject of tumors in animals concludes
that true neoplasms are very rare in wild animals living under natural
conditions. It should be stated, however, that Brooks refers especially
to higher mammals such as are found in zoological collections.
TUMORS OF WILD RATS.
A new growth is found approximately once in every thousand rats examined
in San Francisco. Ninety-two tumors have been examined microscopically.
Time has been available for the study of but one or at the most two
sections from each tumor and while in some cases the diagnosis was
easily made in others there was room for considerable difference of
opinion as to the nature of the growth. It is obvious that it is hardly
fair to expect to make a final diagnosis in every case from one or two
sections taken from one part of the growth, and it is possible that
further study will throw more light upon the histological nature of some
of them.
_Location._—The largest number of the tumors have been found in the
subcutaneous tissue of either the thorax or of the abdomen, and as the
majority of these have been found in female rats we have assumed that
they were probably of mammary origin. The growths were occasionally
located directly under the nipple, but in such cases the nipple was not
retracted, and it was exceptional to find any ulceration. The tumors
were very rarely adherent to the surrounding tissue. After the
subcutaneous tissue tumors were found most frequently in the liver.
Histologically, the most of these growths were sarcomas and the majority
of them had a parasite, the _Cysticercus fasciolaris_, in some part of
the tumor. This parasite, as is well known, is the larval stage of a
tapeworm found in the cat. These tumors of the liver were frequently
associated with an enormous number of secondary growths varying in size
from a millet seed to 1 centimeter in diameter scattered through the
omentum, mesentery, and other abdominal structures.
Several growths have been found in the kidney, mostly of an epithelial
nature, one being a particularly well-marked example of a cystic
papilloma. A few have been found in connection with other parts of the
genito-urinary tract. A large bloody tumor, which upon microscopical
examination was found to be an angiosarcoma, replaced a testicle. A
large growth, apparently an endothelioma, was found near the end of one
horn of the bicornuate uterus.
METASTASES.
Metastases have been found in a number of cases of sarcoma and a smaller
number of cases of the epithelial growths. Most frequently the secondary
tumors were in the liver, the mesentery or the kidney.
_Size._—In proportion to the size of the rat the tumors were quite
large, scarcely any under 1 centimeter in diameter having been observed,
and they varied from this to a growth several centimeters in diameter.
HISTOLOGICAL STRUCTURE.
The following tumors may be regarded as of the connective tissue type:
LIPOMATA.
One typical lipoma has been found. It was located in the subcutaneous
tissue of the thorax and was similar in gross and microscopical
appearance to the tumors of the same nature in man.
FIBROMATA.
A considerable number of subcutaneous tumors have been typical hard
fibromas, others were fibromas in which there were a few cell nests that
led to the suspicion that perhaps a malignant change was taking place in
the tumor, or that a malignant growth was being converted into one of a
benign nature.
SARCOMATA.
Typical spindle cell sarcomas have been encountered a number of times. A
few round cell sarcomas were found in which there were usually a number
of giant cells, but hardly enough to justify one in designating the
growths as giant cell sarcomas. Several other growths have been seen
which gave the impression of being sarcomas but left one in some doubt
as to whether the tissue might not be of the nature of a granuloma.
Many tumors of the epithelial type were encountered which may be classed
together.
ADENOMATA AND CARCINOMATA.
Several very typical adenomas and cystic adenomas have been found. A few
tumors were observed that presented the appearance of carcinomas. A
large number of growths were observed that apparently stood between the
adenoma and the carcinoma and there was room for legitimate difference
of opinion about any one of these, and in fact, different pathologists
who have examined sections of these tumors have expressed different
opinions as to the nature of the growths.
REFERENCES.
Endnote 101:
Hanau (Fortsch. der Med., vol. 7, 1889, May 1, p. 321).
Endnote 102:
Herzog (Journal Med. Research, 1902, vol. 8, old series, p. 74).
Endnote 103:
Loeb (Journal Med. Research, 1901, vol. 6, p. 28; also vol. 3, p. 44,
and vol. 17, p. 299).
Endnote 104:
Flexner and Jobling (Journal Am. Med. Assn., 1907, vol. 48, p. 420).
Endnote 105:
Gaylord and Clowes (Journal Am. Med. Assn., 1907, vol. 48, p. 15).
Endnote 106:
Tyzzer (Journal Am. Med. Assn., 1906, vol. 47, p. 1237).
Endnote 107:
Loeb (Univ. of Pa. Med. Bull., 1907, vol. 19, No. 5).
Endnote 108:
Tyzzer (Journal Med. Research, vol. 17, No. 2, p. 155).
Endnote 109:
Ehrlich and Apolant (Berl. klin. Woch., 1907, vol. 44, pp. 399 and
1401).
Endnote 110:
Saul (Centralblatt für Bact., etc., Aug. 27, 1907, vol. 47).
Endnote 111:
Saul (Centralblatt für Bact., etc., 1909, vol. 49, p. 4).
Endnote 112:
Tyzzer (Journal Med. Research, vol. 17, No. 2, p. 137).
Endnote 113:
Simon (International Clinic, vol. 2, 18th series).
Endnote 114:
Haaland (Berlin, klin. Woch., 1907, vol. 44, p. 73).
Endnote 115:
Ehrlich, Apolant and Haaland (1906, Berlin, klin. Woch., vol. 43, No.
2).
Endnote 116:
Gay (1909, Journal Med. Research, Vol. XX, No. 2).
Endnote 117:
Brooks (1907, Am. Jour. of Med. Sciences, Vol. CXXXIII).
THE ECTOPARASITES OF THE RAT.
By NATHAN BANKS,
_Assistant Entomologist, Bureau of Entomology_.
The ectoparasites of the rat fall naturally into three groups, the
fleas, the lice, and the mites. These three groups are widely separated
from each other, the mites belonging to the class Arachnida, having four
pairs of legs, no segmentation to the body, no antennæ, and no compound
eyes. The fleas and lice belong to the class Insecta. The lice are near
the order Hemiptera, sucking insects without a complete metamorphosis,
while the fleas are related to the Diptera and pass through a complete
metamorphosis. All of these three groups, however, agree in one
character—they are wingless. The mites and lice have flattened or
depressed bodies, while the fleas have compressed bodies. All three
groups have many other species which infest various other animals. Few,
if any, of these parasites confine themselves to the rat, and all can
walk or jump in the adult condition, so that they can easily transfer
their attentions from one rat to another or to some other host. The
majority of them are known to occur on mice, and several of the fleas
and mites will readily attack man.
FLEAS—SIPHONAPTERA.
These wingless, compressed insects are known to all, but few have taken
the trouble to look at them with much care. The adult female flea
deposits her eggs among the hairs or fur of the host animal, but, unlike
the eggs of many parasites, these are not fastened to the hairs and fall
freely to the ground. These eggs are oval, whitish, and smooth, and
about one-half millimeter long. The larvæ escape from the eggs in two to
five days. They are enabled to break the eggshell by a slender process
on the top of the head which disappears after the first molt. This larva
is a slender, legless, cylindrical creature, whitish or yellowish in
color, with a head and 13 segments. There are a few scattered hairs or
bristles on the body and at the tip is a pair of corneous processes. On
the upper part of the head is a pair of short, slender appendages, the
antennæ or feelers. At the front of the head is a pair of biting jaws or
mandibles. These larvæ feed on almost any kind of refuse; some have been
reared on the sweepings from rooms. There is always some organic matter
in this refuse, and this is doubtless their nourishment. The larvæ in
houses usually crawl into cracks or under carpets and feed on the dust
that occurs in such places. Those that infest wild animals probably feed
on the refuse in the nests or retreats of these animals. They remain in
the larval stage from a week to ten days, sometimes two weeks, molting
the skin three times in this interval. Then they spin flat, white,
silken cocoons, in which they transform to the pupal stage. Sometimes
the cocoon is covered with particles of dust. In from five to eight days
the adult flea emerges from the cocoon. The period of their
transformation is affected by the temperature and moisture. In warm,
damp weather a generation may develop in ten days or two weeks, but
usually about eighteen days to three weeks elapse from the egg to adult.
Although some moisture seems necessary to their development, an excess
is apt to destroy the larvæ.
[Illustration:
FIG. 6.—Flea, showing the various parts.
]
The leaping ability of adult fleas is familiar to all. No part of the
leg is particularly enlarged, so that the jump is made by the entire leg
as in the leaf-hopper insects, and not by the hind part of the leg as in
grasshoppers and flea-beetles. The size of fleas is not as variable as
in many insects. Most are about 2 to 3 millimeters long, while the range
is about 1.5 to 6 millimeters. The adult flea has a hard, strongly
chitinized body. The head is small, and on each side bears a short
jointed antenna, which may repose in a groove or depression. Most
species have a small, simple eye, but several forms are normally without
eyes. The sides of the head below the antennæ are called the genæ. At
the lower front end of the head is the mouth and mouth parts. The latter
consist of a pair of triangular maxillæ with jointed maxillary palpi and
a beak or proboscis made up of one median and four lateral pieces. The
outer pair of lateral pieces is the labrum with the imperfectly jointed
labial palpi. They serve as a sheath for the other organs, which are
more slender. The inner pair of pieces are considered to be the
mandibles and the median piece a labrum or hypopharynx. Others call this
piece the unpaired piercing organ, the lingua, or the syringostome.
There are other interpretations of the homologies of the mouth parts,
but the above is the most generally adopted one. The labrum and the
mandibles are roughened and constitute the piercing organs which the
flea inserts into the host to tap a blood vessel. On the lower part of
the head there is frequently a series or comb of stout spines. Similar
spines sometimes occur on the posterior border of the pronotum. These
series of spines are called “ctenidia,” and they are of great value in
classification. Behind the head are three segments, or zoonites, each
bearing a pair of legs. These together form the thorax. The upper
surface is called the notum (pronotum, mesonotum, etc.). The sides are
the pleura—sometimes “epimera” is used; and the ventral part is the
sternum. Each of the thoracic segments has a spiracle, or a breathing
pore, on each side. The first segment of the thorax, called the
“prothorax,” is shorter than the others, and, as above stated,
frequently has a row of ctenidia, or spines, on its posterior border.
The next segment is the mesothorax, and the third the metathorax. The
metathorax usually has some stout bristles in rows on its pleura, which
are enlarged and called “epiphyses,” formerly called “squama aliforme.”
The basal one or two segments are sometimes partly covered by the
epiphyses or the metathorax. These segments consist of a dorsal plate,
or tergite, and a ventral plate, or sternite. Behind the thorax is the
abdomen of 9 apparent segments. Seven of these segments have a spiracle
or breathing pore on the sides. The last segment, or pygidium, bears the
genital organs; in the male certain processes called “claspers” at each
side of the genital opening. The anal aperture is at the end of the
ninth segment between the dorsal and ventral plates. The claspers have a
main curved part, and a slender backward projection called the
“manubrium,” and at the apex an articulated clawlike process called “the
movable finger.” At the tip of the abdomen of the female there is a
short median piece called the “style.” The legs consist of five parts:
The coxa, a large basal piece; the trochanter, a minute piece at the end
of the coxa; the femur, which is usually slightly swollen in the middle;
the tibia, which usually has stout bristles or spines on its posterior
side; and the tarsus, which consists of five parts or joints. The basal
joint is often the longest, and the comparative lengths of these joints
is expressed by a formula, as 60–45–32–18–30. The last, or fifth, joint
has been called the “metatarsus,” but this name is better applied to the
basal joint. At the tip of the last tarsal joint is a pair of stout
claws. The coxæ of legs II and III show a longitudinal suture.
Fleas as a rule prefer certain hosts, but are not as particular in this
regard as are many parasites. Those species which are best known are
found to attack several hosts, including man. This catholicity of taste
is what makes them dangerous parasites, the possible transmitters not
only of plague, but also of consumption, leprosy, etc. The fleas are
treated by various writers under other names, such as _Aphaniptera_, and
_Suctoria_. About 300 species are described, and perhaps as many more
will be gathered by collectors. Formerly all fleas were kept in the
genus _Pulex_; now they are arranged in many genera, and these genera
grouped into families. No less than eight such families are recognized
by some authorities on this group. The species that occur on rats belong
to three families, which may be separated as follows:
1. Thoracic segments much shortened and constricted;
labial palpi apparently not jointed; third joint
of antennæ without subjoints; no ctenidia;
abdomen of female becomes more or less swollen _Sarcopsyllidæ_
Thoracic segments not shortened nor constricted;
labial palpi with joints; third joint of antennæ
with several more or less distinct subjoints;
ctenidia often present; abdomen of female never
distinctly swollen 2
2. Posterior tibial spines in pairs _Pulicidæ_
Posterior tibial spines mostly single and more
numerous _Ctenopsyllidæ_
CTENOPSYLLIDÆ.
To this family belongs the _Ctenopsylla musculi_ Dugès.
This was formerly placed in the genus _Typhlopsylla_. The head is rather
acute in front and has four ctenidia each side; the eyes are very small;
the pronotal comb has 22 spines; each dorsal segment of the body has two
rows of hairs; the basal row of smaller hairs. The proportions of joints
in the hind tarsus are: 45–25–17–8–14. Length 1.8 to 2.5 millimeters.
This species is abundant on rats and mice in Europe and other countries;
recently it has been taken in California and Florida on rats and mice.
PULICIDÆ.
This family includes the greater number of fleas. They have been
arranged in many genera, six of which have been taken from rats. These
are separable as follows:
1. Head without ctenidia; eyes distinct 2
Head and pronotum with ctenidia; last tarsal joint
with four pairs of lateral spines 5
2. Pronotum with ctenidia; female with one
antepygidial bristle on each side _Hoplopsyllus_.
Pronotum without ctenidia 3
3. Last tarsal joint with four pairs of lateral
spines; female with one antepygidial bristle each
side 4
Last tarsal joint with five pairs of lateral
spines; female with two to five antepygidial
bristles each side _Ceratophyllus_.
4. Mesosternite very narrow, without internal rod-like
incrassation from the insertion of coxa upward _Pulex_.
Mesosternite with a rod-like internal incrassation
from the insertion of coxa upward _Xenopsylla_.
5. Eyes rudimentary; female with two to five
antepygidial bristles each side _Neopsylla_.
Eyes distinct; female with but one antepygidial
bristle each side _Ctenocephalus_.
_Hoplopsyllus_, one species, described as a _Pulex_.
_Hoplopsyllus anomalus_ Baker.
The mandibles scarcely reach halfway down on the anterior coxæ; upon
each are two large spines; the pronotal comb has about nine spines each
side; and each abdominal segment has but a single row of bristles. The
hind femora have six to eight bristles on the side; the proportions of
the joints in the hind tarsus are: 26–16–8–5–13. Color, dark reddish
brown. Female, 2.5 millimeters; male, 1.5 millimeters.
Described from a spermophile from Colorado and recorded by Doctor Fox
and Professor Doane from _Mus norvegicus_ from California.
_Pulex._—Of this, the typical genus of the family, but one species has
been recorded from rats.
_Pulex irritans_ Linn.
The mandibles reach about halfway down on the anterior coxæ; the head is
regularly rounded in front; there are no transverse rows of bristles on
the vertex, and but one row of bristles on each abdominal tergite. The
proportions of the joints in the hind tarsus are, 50–30–18–12–32. Color,
usually yellow brown. Male, 1.6 to 2 millimeters; female, 2 to 3.5
millimeters.
This, the human flea, is quite cosmopolitan, but more abundant in warm
countries than elsewhere. It occurs on many domestic animals and has
frequently been taken from rats in California and elsewhere; it also
occurs on skunks.
_Xenopsylla._—This genus includes the following species, formerly placed
in the genus _Lœmopsylla_.
_Xenopsylla cheopis_ Rothschild.
The mandibles reach nearly to the end of the anterior coxæ; there are no
ctenidia on the head or pronotum; the eyes are distinct; each abdominal
tergite has but one row of bristles; the hind femur has a row of about
eight bristles; the proportions of the joints in the hind tarsus are as
follows: 46–30–16–10–20. Color, light brown. Male, 2.5 to 3.5
millimeters; female, 4 to 5.5 millimeters.
This is a true rat flea, but will readily bite man, and is the species
chiefly concerned in transmitting the bubonic plague. It is widely
distributed, especially in seaport towns.
_Ceratophyllus._—Fleas of this genus are abundant on many kinds of small
mammals, especially rodents. There are a great many species and some are
so closely related that it is not easy to identify them. Of the eight
species recorded from rats, four have been taken in this country. It is
not practicable to tabulate these eight species, but the four that occur
in our country may be arranged as follows:
1. Hind tarsal joint II with an apical spine much
longer than joint III _acutus_.
Hind tarsal joint II with spines not longer than
joint III 2
2. Pronotal comb of about 26 spines _niger_.
Pronotal comb of about 18 or 20 spines _fasciatus_ and
_londiniensis_.
_Ceratophyllus niger_ Fox.
This species has the pronotal ctenidia of about 26 spines; there are a
few hairs on the inner surface of hind femur; apical spines of second
joint of hind tarsus not longer than third joint; three hairs in front
of the eye and three in front of these; movable finger of claspers with
five slender bristles on the outer edge. Color, very dark brown. Length
3.5 millimeters.
Taken in California from _Mus decumans_ and from man.
_Ceratophyllus acutus_ Baker.
This species is readily known by having a spine at tip of the second
joint of hind tarsus longer than the third joint and reaching over onto
the fourth joint; the abdominal tergites have each two rows of bristles;
the male claspers are very large and long, sickle shaped. Color, pale
brown. Length, 3 to 3.5 millimeters.
It was described from a spermophile, but Doctor Fox has taken it once
from a rat in California.
_Ceratophyllus fasciatus_ Bosc.
There are 18 or 20 spines in the pronotal comb; there are three bristles
in front of eye and in female two, and in male four in front of these;
there are three or four hairs on the inner surface of the hind femur;
the proportions of joints in the hind tarsus are 50–33–20–11–21. The
manubrium of the male claspers is very long and slender, and some of the
bristles on the movable finger are as long as the joint. Length, male,
1.8 millimeters; female, 2.5 millimeters.
It has been recorded from California on rats, mice, skunks, and man. It
is also common in Europe and elsewhere on rats, mice, and other small
animals.
_Ceratophyllus londiniensis_ Rothschild.
This is allied closely to _C. fasciatus_, and is best separated from
that species by the shape and armature of the genital parts; the
manubrium is not as long as in that species, and the bristles on the
movable finger are shorter; the third joint of the maxillary palpi is
proportionally longer than in _C. fasciatus_. There are three bristles
in front of the eyes and four or five in front of these; there are a few
hairs on the inner surface of the hind femur; the proportions of the
joints in the hind tarsus are 46–30–18–11–18.
It has been recorded by Doctor Fox from _Mus rattus_ in California, and
is known from rats and mice from several parts of Europe; the _C.
italicus_ Tiraboschi is the same species.
The four other species of this genus found on rats and not yet found in
our country are closely related to _C. fasciatus_, and distinguished
chiefly by the shape of the male genitalia.
_Ceratophyllus mustelæ_ Wagner.
This species has no series of hairs on the inner surface of the hind
femur; there are three bristles in front of the eye and six in front of
these; the pronotal comb has 18 or 20 spines; the proportions of the
joints in the hind tarsus are 47–37–20–13–20; the movable finger of the
male clasper has a long process below not seen in other forms. Occurs
(according to Rothschild) on rats in Europe.
_Ceratophyllus pencilliger_ Grube.
This species also has no hairs on the inner surface of the hind femora.
The pronotal comb has 18 spines; there are three bristles in front of
the eye and four in front of these; the proportions of the joints in the
hind tarsus are 52–36–23–14–24; the outer corner of the movable finger
of the male clasper has two little rounded processes. It was described
from Siberia, but according to Rothschild occurs on rats in Europe.
_Ceratophyllus consimilis_ Wagner.
This species is very close to _C. fasciatus_, and has some fine hairs on
the inner surface of the hind femur; there are but two bristles in front
of the eye and in front of these a few finer hairs; the proportions of
the joints in the hind tarsus are 42–30–20–11–19; pronotal spines 18.
Occurs on rats in Russia.
_Ceratophyllus lagomys_ Wagner.
This species also has a few fine hairs on the inner surface of the hind
femur; 18 spines in pronotal comb; there are three bristles in front of
eye and one in front of these; the proportions of the joints in the hind
tarsus are 53–32–20–11–22; the outer corner of the movable finger of the
male clasper has two little processes, similar to those on _C.
pencilliger_. Occurs on rats in Europe.
_Ctenocephalus._—The common fleas on cats and dogs, as well as on man,
belong to two species long kept under one name (_C. canis_ or _C.
serraticeps_), but lately shown by Rothschild to be distinct. Both have
a comb of 8 spines on the head and 16 spines in pronotal comb; the
proportions of joints in the hind tarsus are 40–24–15–10–24. Both are
occasionally taken on rats in this country. They may be separated as
follows:
1. In the female the head is fully twice as long as
high (seen from side); the first spine of genal
comb is two-thirds the length of the second; in
male the manubrium of claspers is barely enlarged
at tip; and with two rows of hairs on disc of _C. felis_
movable finger Bouché.
In the female the head is less than twice as long
as high (seen from side); the first genal spine
in the head comb is only about one-half the
length of the second; in the male the manubrium
of clasper is very distinctly enlarged at tip;
but one row of hairs on the disc of the movable _C. canis_
finger Curtis.
_Neopsylla._—One species of this genus has been described from the brown
rat in Europe.
_Neopsylla bidentatiformis_ Wagner.
The eyes are very small; there are 4 pairs of lateral spines beneath the
last joint of the hind tarsus; the comb on head consists of but 2 stout
spines, below the middle of the antennæ; the pronotal comb has 18
spines; the proportions of the joints in the hind tarsus are
43–33–21–12–21.
Length: Male, 2 to 2.3 millimeters; female, 2.3 to 2.5 millimeters.
Not yet found in the United States; described from Russia.
SARCOPSYLLIDÆ.
The fleas of this family are commonly called “chigoes,” “jiggers,” or
sand fleas. The head is usually larger proportionally than in the other
fleas; there are no ctenidia on head or pronotum; the thoracic segments
are extremely short, and in the female the abdomen enlarges with the
development of the eggs. They do not hop about as other fleas, but
remain on the spot to which they have attached until they die.
Frequently the adjacent skin grows over them, forming a swelling of
considerable size.
Three species belonging to two genera have been recorded from rats.
1. Angle of head acutely produced; fifth tarsal joint
of hind legs without heavy spines; few spines on
the legs _Sarcopsylla_.
Angle of head not produced, obtuse; fifth tarsal
joint with heavy lateral spines, and other spines
on other parts of the legs _Echidnophaga_.
_Echidnophaga._—Two species of this genus are known from rats; one,
however (_E. gallinacea_), can hardly be called a normal parasite, but
rather of accidental occurrence. The genus has also been called
_Argiopsylla_ and _Xestopsylla_.
1. Bristles at end of second joint of hind tarsus
about as long as next three joints; palpi about _E.
one-half the length of mandibles rhynchopsylla_.
Bristles at end of second joint of hind tarsus
about as long as next two joints; palpi about
two-thirds the length of the mandibles _E. gallinacea_.
_Echidnophaga rhynchopsylla_ Tiraboschi.
The body is about twice as long as broad and shining brown; there is but
one hair in front of eye, and four on each metathoracic pleuron;
mandibles larger than in _E. gallinacea_, and the spiracles are much
higher up on the sides than in that species. Length, 1.4 to 1.8
millimeters.
Taken from _Mus rattus_ in Italy.
_Echidnophaga gallinacea_ Westwood.
This species has the body almost as broad as long, and of a red-brown
color; 1 bristle in front of eye and 6 on each metathoracic pleuron;
each abdominal tergite has on each side near the median line a single
hair; the spiracles are situated well down on the sides. Length: Male,
0.8 to 1.2 millimeters; female, 1 to 1.8 millimeters.
This species is a fairly common pest of poultry and dogs in warm
countries, and is called the “chicken flea.” It has been taken from rats
in Italy.
_Sarcopsylla._—This genus includes the _S. penetrans_, which attacks the
feet of various animals, including man, in the Tropics. This species has
not yet been recorded from rats, but an allied species is described from
Brazilian rats.
_Sarcopsylla cæcata_ Enderlein.
Color, clear yellowish. Eyes rudimentary; lower anterior corner of coxæ
prolonged in a tooth; tarsal joints very short; claws long, but little
curved, and almost hair like. The body of a swollen female is about 5
millimeters long.
Taken from _Mus rattus_ in Brazil.
LICE—ANOPLURA.
The insects known as Pediculi, or lice, are parasitic during their
entire life on various mammals, including man. They are flat, rather
elongate, wingless insects, with a small head and stout legs, which end
in a strong claw, opposable to a projection at the tip of the
penultimate joint. The simple antennæ, three to five jointed, are
inserted in a concavity on the side of the head. The mouth parts are of
a very peculiar nature, and not yet homologized with the cibaria of
other insects. There is a short beak or proboscis in front, with
recurved spines or hooks on its dorsal and lateral surfaces. Through
this beak extends a slender stylet, that is formed of three parts; a
ventral channeled piece, perhaps a labium; a dorsal piece, consisting of
two pieces fused together, perhaps the maxillæ; and a median tube,
possibly the hypopharynx. The stylet is used to pierce the skin of the
host, and the blood is sucked up through it. There are no palpi. On each
side of the head there is a small, simple eye. The thorax shows only
incompletely the division into the three parts; there is a large
spiracle above on each side. The abdomen shows eight segments, six of
them have a spiracle, or breathing pore, on each side, the basal and
apical segments being without them. All of the segments bear a few
simple hairs or bristles; the longest are on the posterior segments. The
legs are stout and prominent; they consist of a broad coxa, a small
trochanter, a longer femur, a tibia with an apical process, and a tarsus
of one joint and a very large terminal claw. At the apex of the tibia,
just within the projection, is a sucking disc. This, the projection, and
the claw form the apparatus to hold fast to the hair of the host.
Lice usually walk sideways, but do not travel much, and they keep close
to one host. The eggs are slightly elongate and fastened to the hair of
the host. They hatch in about ten to fifteen days, the young coming out
of the top of the egg. These young do not differ much in structure from
the adults, but are paler in color. They molt their skin a few times,
probably four, before they reach the mature condition. The males are
less numerous than the females, and ordinarily smaller. There are
several generations each year, dependent doubtless on the temperature;
but the life history is not thoroughly known for any species. After
sucking the blood the abdomen of the louse becomes somewhat distended,
very noticeably so in some species.
The sucking habits of the lice render them dangerous parasites and
capable of transmitting a disease from one host to another. Fortunately
they do not readily change hosts so that they can not be considered
quite as dangerous as some more active parasites. However, several
species have already been shown to carry diseases in laboratory
experiments. Therefore it is probable that some of them will be
connected with the origin and diffusion of certain diseases of animals.
[Illustration:
FIG. 7.—Louse (_Polyplax spinulosa_).
]
The Anoplura, or lice, have often been treated in connection with the
Mallophaga, or biting lice. This is doubtless because they frequently
occur on the same animal, and have a general resemblance to them.
However, they have no real affinity to these insects, and the general
opinion is that they are more or less related to the Hemiptera.
Sometimes they are treated as a group or section of the Hemiptera, but
also as a separate order, under various names as Siphunculata,
Lipognatha, Pseudorhynchota, and Ellipoptera.
There are about 50 or 60 known species which are arranged in 15 genera
and 4 families. Four species belonging to three different genera have
been recorded from rats; a number of others are known from mice and
other rodents, and some of these will probably yet be taken upon rats.
These four forms are separated, as follows:
1. Eyes large and distinct; beak very short; thorax _Pediculus
plainly longer than broad capitis_.
Eyes small, beak longer; thorax about as broad as
long 2
2. In male the pleura of abdominal segments 3 to 6
above and below have a prominent tooth-like _Hoplopleura
projection; a tooth on the hind femur of female acanthopus_.
In male the pleura of abdominal segments without
such projections; no tooth on hind femur of
female 3
3. Last joint of antennæ much more slender than those
before; an acute tooth at sides of segments 4 to
7; head much narrower in front; antennæ _Polyplax
two-thirds as long as head miacantha_.
Last joint of antennæ not much more slender than
others; head quite broad in front; antennæ as _Polyplax
long as head spinulosus_.
_Pediculus capitis_ De Geer.
It is pale grayish in color, with faint dark markings at the sides of
the thorax and abdomen; the last segment of the abdomen in female is
bilobed. The head is longer than broad and tapers in front. Length, 2
millimeters. This is the head louse of man, and is said to have been
taken from rats, and is claimed to be able to transfer plague from rats
to man. Its occurrence on rats, however, appears to be very uncommon.
_Hopopleura acanthopus_ Burmeister.
In the male the pleura of the abdominal segments 3 to 6, which reach up
on the dorsum and over on the venter, have at their inner ends a
prominent projection, toothed in all except the third on dorsum and the
sixth on venter, which are spine-like. The head is but little longer
than broad, broad in front; and in the female there is a recurved tooth
on each hind femur. The last segment of the female abdomen is bilobed
behind. Length, 1.3 millimeters. It has been taken from rats in Europe,
but is more common on species of _Microtus_.
_Polyplax spinulosus_ Burmeister.
The sides of the abdominal segments are acute, but the males do not have
the large tooth-like projection of _Hoplopleura_. The last segment of
the female is truncate; the head is about as broad in front as behind,
and the legs are very short and stout; the antennæ are as long as head,
and the last joint is but little smaller than the others. Color, pale
yellowish. Length, 1.4 millimeters.
This is the common rat louse, and is probably as widely distributed as
its host. Specimens have been taken in both the eastern and western
parts of the United States.
_Polyplax miacantha_ Speiser.
This differs from _P. spinulosus_ in having a longer and narrower
anterior part of head, in that the last joint of the antennæ is more
slender, and the antennæ are only two-thirds as long as the head. The
abdominal segments 4 to 7 show an acute process at the sides. Length,
1.5 to 1.75 millimeters.
Taken from rats in Abyssinia.
MITES—ACARINA.
The mites (order Acarina, class Arachnida) are readily known from the
insects (fleas and lice) by having four pairs of legs, no antennæ, and
the abdomen does not show any segmentation, nor is there usually any
distinction between head and thorax. In some groups there is a small
head-like part, called the capitulum. The mouth parts consist of a pair
of mandibles (often styliform or needle-like), a lip, and a pair of
palpi. In some forms there is a central piece, called the hypopharynx,
and in other groups is a plate above the mouth parts, known as the
epistome. The body usually shows more or less distinctly a division into
two parts—the anterior, called the cephalothorax, and the posterior the
abdomen. However, in many mites it is not possible to separate these
parts, except that it is considered that the legs are borne by the
cephalothorax. In many forms there is a small, simple eye each side on
the cephalothorax, but many other forms are blind. Some species have a
tracheal system, which opens in a pair of spiracles near the hind legs
or near the anterior end of the body; other species have no definite
respiratory system. The genital aperture is on the venter, usually
between the legs. The legs consist of the usual joints—coxa, trochanter,
femur, tibia, sometimes a metatarsus, and a tarsus. The tarsus
terminates in a pair of claws, sometimes three or only one, and often a
sucker or caroncle. Most mites are not parasitic; those species that are
parasitic are often free in one stage. The parasitic mites suck the
blood of their host, feed on the hair or dermal scales, or burrow in the
skin. Some predaceous species inhabit animals to hunt and eat the
parasitic mites that infest that animal.
The mites that occur parasitically on rats belong to four families:
Sarcoptidæ, Cheyletidæ, Ixodidæ, and Gamasidæ.
1. A distinct spiracle or breathing pore on each side
of body near coxæ III or IV 2
No such spiracle or pore visible 3
2. A small, distinct head part in front of the body;
palpi three jointed; a granulate area around the
spiracle; no sternal plate _Ixodidæ_.
No such head part; palpi five jointed; no granulate
space around spiracle, but a long, chitinized
piece reaching forward from it; a more or less
distinct sternal plate _Gamasidæ_.
3. All legs simple, unmodified, ending in a stalked
sucker _Sarcoptidæ_.
Front legs short, enlarged, and modified for
clasping; all legs end in one or two stout claws _Cheyletidæ_.
IXODIDÆ.
The Ixodidæ, or ticks, are rather large, flat, leathery-skinned mites,
which suck the blood of various animals. In the male the dorsum of the
body is nearly covered by a corneous shield, while in the female this
shield occupies only the anterior part of the body. In the female the
body swells to enormous proportions as she engorges herself on the blood
of the host. At the posterior margin of the body there are in many forms
a series of lobes or festoons. There is no species of tick that is
commonly found on rats, but four species that normally infest other
animals have been taken from them.
[Illustration:
FIG. 8.—Mite (_Lælaps echidninus_).
]
1. On the venter is a groove in front of the anus and
extending back each side; no festoons to _Ixodes
posterior margin of body; palpi rather long ricinus_.
On the venter there is no groove in front of the
anus, but usually one behind; festoons distinct
in males and unengorged females 2
2. Palpi very short with transverse ridges; shield of
female narrowed behind eyes; stigmal plate nearly _Margaropus
round annulatus_.
Palpi short, without transverse ridges; shield of
female not narrowed behind eyes; stigmal plate _Rhipicephalus
comma shaped sanguineus_.
Palpi elongate, without ridges; shield of female _Hyalomma
broad; stigmal plate oval, aegypticum_.
_Ixodes ricinus_ Linné.
The shield of the female is elliptical, plainly longer than broad, sides
not suddenly narrowed behind, and there is no eye-spot at each lateral
corner. The coxa I has a long sharp spine.
This is a common European tick found on sheep, cattle, dogs, etc., and
it has been taken a few times in this country. Neumann has recorded its
capture from _Mus decumans_.
_Margaropus annulatus_ Say.
The shield is plainly longer than broad, with a distinct eye-spot at
each lateral corner, and behind the eye the shield is suddenly narrowed;
the coxæ of the female are without spines, but the male has 2 on coxæ I.
This is the common cattle tick of the United States, and disseminates
the Texas fever. Mr. Hunter has taken it once from a rat in a barn at
Dallas, Tex.
_Rhipicephalus sanguineus_ Latreille.
The shield of the female is oval, and longer than broad, with an
eye-spot at each outer corner. Coxa I with 2 teeth; a smaller tooth on
each of the other coxæ. Stigmal plate long, comma shaped. In the male
there is a corneous plate each side of the anus, and on middle of
posterior margin a projection, or short tail.
This species is common in tropical countries, and Nuttall has recorded
specimens from the black rat in India.
_Hyalomma aegypticum_ Linné.
The shield of the female is as broad as long, and the eye-spot is
slightly above each outer corner. Coxa I has 2 large teeth, and a small
tooth on each of the other coxæ. In the male there are 2 corneous plates
each side of anus, and behind is a pair of small tubercles.
This is a common tick in the warmer parts of the Old World; and Nuttall
has recorded young specimens on the black rat.
GAMASIDÆ.
The Gamasid mites, although much smaller than the ticks, are large
enough to be seen by the naked eye. They are active, and most are not
parasitic, at least for part of their time. The palpi are simple, of 5
joints; the mandibles are elongate, retractile, and usually chelate at
tip. There are no eyes. The dorsum and often the venter shows one or
more corneous shields or plates, frequently a number of them; one or two
on the dorsum, and on the venter one between the coxæ, called the
sternal plate; one behind this, the genital plate; one behind the
latter, the ventral plate; and one surrounding the anus, the anal plate.
Frequently some of these are absent or united to one of the others.
The legs are slender, usually of 6 joints, with a long tarsus that
terminates in 2 claws, and often a sucker, or caroncle. The stigmata, or
spiracles, are lateral above and between coxæ II and IV, and usually
provided with a slender peritreme reaching forward toward the head.
Nearly all the Gamasidæ deposit eggs, and the young often differ
considerably from the adult in structure. There are two, and perhaps
sometimes three, nymphal stages. In one of these nymphal stages the mite
is apt to attach itself to an insect for the purpose of being carried to
a similar locality, where it may feed and mature. The coprophagous and
xylophagous insects are especially concerned in the diffusion of these
mites.
There are, however, quite a number of species that are genuine parasites
of insects and other animals. Those occurring on rats belong to two
genera, Myonyssus and Lælaps. They can be separated as follows:
1. Anal plate small, much smaller than the ventral
plate _Lælaps_.
Anal plate large, larger than the ventral plate _Myonyssus_.
_Myonyssus._—This genus is made by Tiraboschi for one species:
_Myonyssus decumani_ Tiraboschi.
Body oval; legs short and stout, all tarsi with a large caroncle with
two short claws; coxæ II have a large tooth on the anterior border, none
of coxæ with spines; sternal plate much broader than long, with three
bristles each side; ventro-genital plate much longer than broad,
broadest behind, bordered with bristles; anal plate very large, nearly
one and a half times as broad as long; three large spines each side on
venter. Length, 0.95 millimeter.
Found in Italy on _Mus decumans_.
_Lælaps._—This genus embraces a large number of species, several of
which occur on small animals, such as the muskrat, ground hog, and
chipmunk. Three have been recorded from rats, one of these from
California. The dorsal plate is covered with hairs or bristles, and
there are usually stout bristles on the margins of the plates on the
venter. There is also a bristle, or a spine, at the tip of the anal
plate. The legs are short and stout, with a distinct caroncle, and two
claws.
1. Dorsum with numerous fine hairs; no stout spines on
coxæ _L. stabularis_.
Dorsum with fewer, but stouter spine-like bristles;
each coxa has a stout spine 2
2. Body but little longer than broad; ventral plate
longer than broad _L. agilis_.
Body much longer than broad; ventral plate about as
broad as long _L. echidninus_.
_Lælaps echidninus_ Berlese.
Dorsum of body almost wholly covered with a shield, with rows (six in
front, eight behind) of stout, curved bristles, a longer pair near front
margin, and some around lateral and posterior margins. Legs short and
stout, tarsi about twice as long as preceding joint; each coxa bears a
stout spine near middle. Palpi very short; sternum with three stout
bristles or spines each side; ventral plate with four stout bristles
each side; anal plate with a stout apical bristle, and a small one each
side. Length, 1 millimeter.
Occurs commonly on rats in warm countries, and known from California. It
may possibly aid in the transmission of disease.
_Lælaps agilis_ Koch.
Similar in many respects to _L. echidninus_ but differ in the shorter
and proportionately broader body, barely longer than broad, and in the
weaker and shorter spines on dorsum and on the ventral plates; there are
also some small short spines on the general surface of the venter.
Length, 0.7 millimeter.
Recorded from rats from Europe and Africa.
_Lælaps stabularis_ Koch.
The body is of the same general shape as in _L. echidninus_, but the
dorsum is clothed with 12 to 18 rows of fine short hairs. The first pair
of legs is more slender than in the other species, and the hind legs are
also more elongate; the coxæ do not have the stout spines seen in the
other species, and the bristles on the sternal and ventral plates are
much less stout; the general surface of the venter has many hairs, the
anal plate has a short apical bristle. Length, 1.2 millimeters.
Taken on the brown rat in Italy; also found in manure.
CHEYLETIDÆ.
This family consists of small, soft-bodied mites, that are parasitic or
predaceous in habits. The palpi are small, three or four jointed; the
mandibles are styliform and retractile; and the breathing spiracles open
near the mouth parts. The species that occur on rats belong to the genus
_Myobia_.
_Myobia._—The body is elongate, fully twice as long as broad, tipped by
a pair of long, stout bristles. The first pair of legs is enlarged and
shortened, with a terminal hook to grasp hairs; the other legs are
short, simple, and far apart. The palpi and mouth parts are very small,
and the dorsum bears stout bristles. They are supposed to feed on the
exudations of the skin, but it would seem more probable, from the nature
of the mandibles, that they pierced the skin to secure food. All are
very small, not one-half a millimeter long. Of the several species two
have been recorded from rats.
1. Dorsum of female with spines all acute and sharp _M. musculi_.
Dorsum of female with some of the posterior spines
flattened and rather scale like _M. ensifera_.
_Myobia musculi_ Schrank.
This occurs on various mice and moles, and once recorded from the brown
rat. It has been taken in this country on mice. It lives at the base of
the hairs.
_Myobia ensifera_ Poppe.
This was described from the brown rat in Europe. The female is separated
from _M. musculi_ by having about six of the posterior dorsal spines
flattened and scale like; in the male the six dorsal spines are longer,
and the small spines much smaller than in _M. musculi_.
SARCOPTIDÆ.
These are the itch and scab mites. The body is soft, rounded, and
whitish in color. The legs are very short, of five joints, and end in
one or two claws, and often a pediceled sucker. The palpi are small and
short, of three joints, but the basal is usually united to the rostrum.
There are no spiracles, and respiration is therefore through the general
surface of the skin. The sexes are often quite different in structure.
The females usually deposit eggs, the larvæ are hexopod, and there are
two nymphal stages. They are all parasites, mostly on mammals and birds,
and often burrow in the skin, causing mange, or scabies.
Only one species has been taken on rats; this belongs to the genus
_Notoedres_.
_Notoedres._—In this genus the third pair of legs of the male and the
third and fourth of the female have no sucker at the tip. The anal
opening is on the posterior part of the dorsum. The three known species
are parasitic on mammals—one on the cat, one on the rabbit, and the
third on rats.
_Notoedres muris_ Mègnin.
This is a rounded mite, with finely striate skin, a small triangular
rostrum; in front the four anterior legs project a little beyond the
body, and each ends in a long pedicellate sucker; the third and fourth
pairs of legs are not visible from above, and each ends in a long
bristle. There are a few short hairs around the anal aperture and about
ten others in front of these. The species measures about 0.3 to 0.4
millimeter long.
It usually occurs about the ears and the genital organs of the host, and
has been taken from both the brown and black rat in Europe. The
_Sarcoptes alepis_ Railliet and Lucet is the same species.
DEMODECIDÆ.
Besides the mites above described, a form of _Demodex_ has been recorded
from rats, but the species is not given. These mites are very tiny, with
elongate body, the posterior part annulate, the front part with eight
very short legs. They inhabit the hair follicles of various mammals.
That on the rat may have been only an accidental occurrence of some
species normally on another animal.
THE INTERNAL PARASITES OF RATS AND MICE IN THEIR RELATION TO DISEASES OF
MAN.
By CH. WARDELL STILES, _Chief_, and CHARLES G. CRANE, B. S., _Assistant,
Division of Zoology, Hygienic Laboratory, United States Public Health
and Marine-Hospital Service_.
SUMMARY.
Rats and mice may harbor 11 species of internal parasites which come
into consideration as possible or established parasites of man. From
this point of view, 7 of the parasites are of more academic interest
than practical importance. The rat may, however, be viewed as the
practical, theoretical, and permanent reservoir for one zooparasitic
disease (trichinosis) of considerable importance, and of at least one,
perhaps two, other zooparasitic infections (“_Lamblia duodenalis_” and
_Hymenolepis diminuta_) of much less importance. Its possible future
rôle in connection with sleeping sickness should not be entirely
ignored.
From the standpoint of internal zooparasitism, therefore, the present
public health interest in rats and mice centers in trichinosis. This
disease will probably never be eradicated from man until rats and mice
are practically eradicated, and any rational public health campaign
directed against trichinosis must take the rat into serious
consideration.
The eradication of rats and mice would be a very substantial
contribution toward a reduction and eradication of trichinosis.
INTRODUCTION.
From the habits of rats, it is to be expected that they harbor many
species of parasites, and on account of their presence in our houses the
question naturally arises as to whether any of these parasites are
transmissible, either directly or indirectly, to man.
The species of internal parasites which come especially into
consideration in this connection are the following:
PROTOZOA: _Chlamydophrys enchelys_ (p. 88), _Lamblia duodenalis_ (p.
89), _Trypanosoma gambiense_ (p. 94).
TREMATODA: None.
CESTODA: _Cysticercus cellulosæ_ (p. 95), _C. fasciolaris_ (p. 96),
_C. pisiformis_ (p. 95), _H. murina_ Duj. [= _fraterna_] (p. 96),
_Hymenolepis diminuta_ (p. 98).
NEMATODA: _Trichinella spiralis_ (p. 101).
ACANTHOCEPHALA: _Gigantorhynchus moniliformis_ (p. 108).
ARACHNOIDEA: _Linguatula denticulata_ (p. 110).
Of these 11 species, the trichina worm (sometimes called the flesh worm)
exceeds all the others combined, both in frequency and importance, as a
cause of disease in man.
PROTOZOA.
Genus CHLAMYDOPHRYS[U] Cienkowski, 1876.
Footnote U:
SYNONYM.—_Leydenia_ Schaudinn, 1896.
Species CHLAMYDOPHRYS ENCHELYS[V] (Ehrenberg.)
Footnote V:
SYNONYMS.—_Difflugia enchelys_ Ehrenberg; _Chlamydophrys stercorea_
Cienkowski; _Leydenia gemmipara_ Schaudinn, 1896; _Chl. enchelys_
(Ehrenberg) Braun.
A very peculiar organism has been described under the name of _Leydenia
gemmipara_ Schaudinn, 1896. This was found in fluid, obtained by
puncture, from two ascites patients in Berlin, Germany. More recently
Schaudinn has concluded that _Leydenia gemmipara_ represents an abnormal
condition of a protozoon known as _Chlamydophrys_. The latter passes
through the intestinal tract of various animals (as man, mice,
squirrels, rabbits, cattle), and thus is occasionally found in fresh
human stools. According to Schaudinn, if pathological conditions in the
colon cause an alkaline reaction of its entire content, the usual shell
formation in _Chlamydophrys_ fails to take place, the organisms then
multiply in an atypical manner by division and budding, and the result
is the structure described as _Leydenia gemmipara_.
Genus LAMBLIA[W] R. Blanchard, 1888.
Footnote W:
SYNONYMS.—_Dimorphus_ Grassi, 1879 (not Haller, 1878, arachnoid);
_Megastoma_ Grassi, 1881 (not de Blainville, mollusk; not Swains.,
1837, bird; not Costa, 1850, fish; not Megerle, mollusk); “_Dimorpha_
Grassi” of Senn, 1901 (not _Dimorpha_ Jur., 1807, hymenopteron; not
Gray, 1840, mollusk; not Hodgs., 1841, bird); _Megastroma_
Schneidemuehl, 1898, misprint.
GENERIC DIAGNOSIS.—_Polymastigidæ_: Body bilaterally symmetrical,
pyriform, excavate antero-ventrally to form a sucker; flagella
directed posteriorly; 3 pairs inserted on margin of the sucker, 1 pair
at posterior end of body. Parasitic in intestine of mammals.
TYPE SPECIES.—_Lamblia duodenalis_ s. l. (“_L. intestinalis_” of man).
Flagellate protozoa belonging to this genus are reported as parasitic in
the intestinal canal of various species of mammals. At present the forms
in question are usually looked upon as belonging to the species _L.
duodenalis_. Evidence is, however, accumulating (p. 92) to the effect
that there are at least three distinct species of _Lamblia_ (“_L.
intestinalis_” of man, _L. muris_ of mice, and _L. cuniculi_ (or
_duodenalis_?) of rabbits). Admitting that there may be three species,
the intertransmissibility of these forms from one host to another
remains to be investigated to some extent. It seems thus far definitely
proved that the form which occurs in man is transmissible to mice,
rabbits, and guinea pigs, hence mice still remain a source of danger in
respect to the infection in man. To exactly what extent this fact is of
academic interest or of practical significance is at present _sub
judice_.
Species LAMBLIA DUODENALIS[X] (Davaine, 1875) Stiles, 1902, s. l.
Footnote X:
SYNONYMS.—_Cercomonas intestinalis_ Lambl, 1859, in man (not _Bodo_
(_Cercomonas_) _intestinalis_ (Ehrenberg, 1838) Diesing, 1850, in
frogs; not _Cercomonas intestinalis_ (Ehrenberg, 1838) Perty, 1852);
_Hexamita duodenalis_ Davaine, 1875, in rabbits; _Dimorphus muris_
Grassi, 1879, in _Mus_; _Megastoma entericum_ Grassi, 1881 (=
_Dimorphus muris_ renamed); _Megastoma intestinale_ (Lambl, 1859) R.
Blanchard, 1885; _Lamblia intestinalis_ (Lambl, 1859) R. Blanchard,
1888; “_Megastoma intestinalis_” of Leclerq, 1890; “_Cercomonas
intistinalis_ Lambl” of L. Pfeiffer; “_Megastroma entericum_ Grassi,
1881” of Schneidemuehl, 1898; “_Dimorpha muris_ Grassi” of Senn, 1900.
[Figs. 9 to 15.]
SPECIFIC DIAGNOSIS.—_Lamblia_ (p. 88): Body pyriform, 5 to 16μ (21μ
Lambl) long, 4 to 12.5μ (8.6 to 11μ Lambl) broad; flagella 9 to 14μ
long; anterior end bluntly rounded, posterior end sharply pointed,
dorsum convex, antero-ventrally concave, venter flat to convex;
antero-ventral concavity forms a sucker, the margins of which project
from the surface and are contractile. Four pairs of ventral
posteriorly directed flagella, arranged as follows: 1 pair insert on
anterior margin of sucker; 2 pairs on posterior margin of sucker, near
median line; 1 pair on posterior extremity. Body membrane (“cuticula”)
very delicate, permitting some change of body form; protoplasm finely
granular; nucleus dumb-bell shaped, pre-equatorial. Vacuoles not
observed. Copulation sucker-to-sucker, followed by an encystation, in
which stage complicated nuclear changes occur; cysts 10 by 7μ.
HABITAT.—Upper portion of small intestine of man (_Homo_); also of the
common house mouse (_Mus musculus_), the brown rat (_M. decumanus_),
the black rat (_M. rattus_), “_Mus sylvestris_” [=? _M. decumanus_],
field mouse (_Microtus arvalis_), water mole (_Arvicola amphibius_),
rabbits, guinea pigs, domesticated cats, dogs, and sheep.
GEOGRAPHICAL DISTRIBUTION.—Europe, Egypt, and United States.
This parasite is very common in animals in certain parts of Europe, and
cases of its presence in man have been reported by a number of authors
(Lambl, 1859; Grassi, 1881; Perroncito, 1888; Moritz, 1891; Moritz &
Holzl, 1892; Roos, 1893; Kruse & Pasquale, 1894; Piccardi, 1895;
Sievers; Mueller; Frshezjesski & Ucke; Stiles, 1902; Braun, 1908; etc.).
The indications are that it is more common in man than is generally
assumed.
Possibly man becomes infected through eating food (as bread, etc.) which
has been soiled by the excrements (containing the encysted stage) of
mice and rats. Grassi infected himself, Perroncito infected mice and
rabbits, and Stiles infected guinea pigs by feeding to them human feces
containing the encysted stage.
The parasite may be present in large numbers. Moritz estimated a
discharge of 18 milliards within twenty-four hours from one of his
patients. It has been observed in healthy persons and also in cases of
various diseases, but especially in children and in cases of
tuberculosis. It is an inhabitant chiefly of the duodenum and jejunum,
where it attaches itself (fig. 13) by means of the sucker to the
epithelial cells. It is rarer in the ileum. In case the stomach is
alkaline (carcinoma) the parasite may occur in this organ (Cohnheim,
Zabel). In P. Schmidt’s case the hydrochloric acid was 1 per cent. In
case the intestinal peristalsis is normal the parasite becomes encysted
in the colon, so that usually only the encysted stage is found in the
feces; but in case of increased peristalsis and diarrhea the organisms
have not time to encyst, so that the free stages are observed in the
stools. As the parasites become cool motion decreases; when raised to
high temperature, as 50° C., motion becomes slow, and the organisms die
at 52° C. or below 0° C.
[Illustration:
FIG. 9.—Lateral view of encysted _Lamblia duodenalis_.
FIG. 10.—Cyst from large intestine.
FIG. 11.—Ventral view of _Lamblia_.
FIG. 12.—Lateral view.
FIG. 13.—Epithelial cells of the villous coating of the small
intestine infested with _Lamblia_. (After
Grassi & Schewiakoff, 1888, pl. 15, figs. 1, 2, 5, 11, 12.)
]
[Illustration:
FIG. 14.—An epithelial cell with parasitic _Lamblia_. Greatly
enlarged. (After Grassi & Schewiakoff, 1888, pl. 15, fig. 6.)
]
[Illustration:
FIG. 15.—An individual in the act of joining an epithelial cell.
(After Grassi & Schewiakoff, 1888, pl. 15, fig. 7.)
]
PATHOGENICITY.—Opinion differs as to the pathogenicity of this organism.
Perroncito (1902b) reports it as causing a fatal disease in rabbits.
Braun (1908) is inclined to consider it harmless. From conversation with
Doctor Hemmeter, we are persuaded that in his case in a child in
Baltimore the parasite was not without effect. Possibly the question as
to its pathogenicity is a relative one in that light infections may
produce no recognizable disturbance, while heavy infections may produce
recognizable effects. Doctor Hemmeter’s original letter regarding his
case contained the following notes:
Patient, male, white child, 3 years old, born in Maryland. Had
recurrent attacks of colitis all its life; three acute attacks within
the last three weeks, accompanied by fever, distended abdomen,
sensitive, etc. Stools have always been like putty, containing large
amount of mucus, and some blood streaks; fever lasting three days, no
pronounced diarrhea, 2 to 3 passages per day; intervals between
attacks variable, stools at such times like putty, also with mucus.
Later information from Doctor Hemmeter states that the disappearance of
the parasites from the stools coincided with improvement in the child’s
condition.
CLINICAL DIAGNOSIS.—The fresh unstained stools should be examined
microscopically; or the diluted stool may be stained with methylene
blue, by which nearly all objects become promptly stained, except
_Lamblia_, which remains grayish white (Roos, 1893) for several hours.
TREATMENT.—Attempts to expel _Lamblia_ have not always met with marked
success. Among the drugs used are male fern, sulphate of quinine,
naphthol, calomel, hydrochloric acid, and arsenic. Grassi appears to
have had success with calcined magnesia.
[Illustration:
FIG. 16.—“_Lamblia intestinalis_” of man. (After Bensen, 1908, fig.
5.)
]
[Illustration:
FIG. 17.—Copulation cyst of “_Lamblia intestinalis_” of man. (After
Bensen, 1908, fig. 5.)
]
THE DIVISION OF _Lamblia duodenalis_ INTO SEPARATE SPECIES.—Bensen
(1908) has recently divided _Lamblia duodenalis_ s. l. into three
species: _L. “intestinalis,”_ _L. muris_, and _L. cuniculi_. His
preliminary paper seems to offer fairly convincing data for the
correctness of his interpretation, but it may be well to await the
publication of his more complete paper, in which he promises fuller
details, before the species are definitely accepted. Several
nomenclatural points will come up for consideration in this connection.
_Lamblia intestinalis_, which Bensen accepts as name for the species
(fig. 16) occurring in man, can not be accepted, as this name is based
on _Cercomonas intestinalis_ Lambl, 1859, which is invalidated by
_Cercomonas intestinalis_ (Ehrenberg, 1838) Perty, 1852, found in frogs.
_Lamblia muris_ (fig. 18) will probably stand, based on _Dimorphus
muris_ Grassi, 1879.
_Lamblia cuniculi._—There is some doubt as to the status of this name.
Davaine (1875a, 128–129) has described from rabbits a protozoon, which
he designated as _Hexamita duodenalis_ and which Railliet (1893a, 169)
identifies as a synonym of _Lamblia intestinalis_ (Lambl). On basis of
the principle that identifications are to be accepted as correct until
shown to be incorrect, Stiles has accepted _duodenalis_ as name (1902)
for the form in question. The question now arises as to the relation of
_cuniculi_ to _duodenalis_. If they are accepted as identical,
_duodenalis_ will supplant _cuniculi_, and a new name must be given to
the form found in man. If _duodenalis_ is taken as identical with
_intestinalis_ Lambl, _duodenalis_ remains as name for the form in man,
and _cuniculi_ Bensen will stand for the species in rabbits. If
Railliet’s interpretation of synonymy be shown to be incorrect by
proving that _duodenalis_ Davaine is not to be considered in connection
with either form, a new name must be given to _intestinalis_ Lambl.
[Illustration:
FIG. 18.—_Lamblia muris_ of mice. (After Bensen, 1908, fig. 1.)
]
[Illustration:
FIG. 19.—Autogametocyte of _Lamblia muris_. (After Bensen, 1908, fig.
6.)
]
Genus TRYPANOSOMA s. l.
An extensive group of parasitic protozoa, known as “trypanosomes,” has
recently been the basis of considerable literature. The genus
_Trypanosoma_ was originally based upon a species (_T. rotatorium_)
found in frogs, and while most trypanosomes have been described as
members of this genus several authors have separated out certain forms
into separate genera.
Luehe (1906) has recently placed the trypanosomes of mammals in the
Genus TRYPANOZOON Luehe, 1906.
One of these species (_Trypanozoon gambiense_, usually known as
_Trypanosoma gambiense_) is the cause of “sleeping sickness” in man, and
has been transmitted in laboratory experiments to rats and mice.
[Illustration:
FIG. 20.—An isolated pork-measle bladder worm (_Cysticercus
cellulosæ_), with extended head. Greatly enlarged. (After Stiles,
1898a, 90, fig. 76.)
]
Just what practical importance there may be in the ability of the
parasite to live in rats and mice remains to be seen, but theoretically
this biological factor may possibly become one of considerable
magnitude. At present the least conclusion to be drawn is that it adds
one more to the many arguments in favor of a world-wide destruction of
rats and mice.
Several trypanosomes, other than _Trypanozoon gambiense_, are
transmissible by experiment to rats and mice, while one species
(_Trypanozoon lewisi_) has rats for its normal host, and two other
species (_Trypanozoon duttoni_ and _Trypanosoma musculi_ Kendall, 1896)
are reported originally from the mouse.
CESTODA—TAPEWORMS.
Of the five cestodes mentioned as coming into consideration in the
subject under discussion, only one (_Hymenolepis diminuta_) need be
considered seriously.
CYSTICERCUS CELLULOSÆ—TÆNIA SOLIUM.
[Fig. 20.]
The larval cestode known as _Cysticercus cellulosæ_ (which causes
“measles” in swine) develops (when eaten by man) into a tapeworm which
is known as _Tænia solium_. This larva is also reported as encysted in
the peritoneum of _Mus rattus_.
[Illustration:
FIG. 21.—Portion of mesentery of rabbit infected with _Cysticercus
pisiformis_. Natural size. (After Railliet, 1893a, 216, fig. 114.)
]
Even if it be granted that the specific determination of the specimen in
question as _Cysticercus cellulosæ_ is correct, the occasional infection
of rats with this parasite would be of very little practical
significance in this country from a public health point of view, as we
do not use rats for food for man. Theoretically it is possible to
conceive of combinations of circumstances in which such infection in the
rat might under certain conditions eventually affect man, but the
chances are so remote as to be negligible, especially when compared with
the much greater questions which demand attention.
CYSTICERCUS PISIFORMIS—TÆNIA PISIFORMIS.
[Fig. 21.]
The larval stage of this parasite occurs in rabbits, the adult stage in
canines. Parona (1901) reports the occurrence of the larval stage in
_Mus brasiliensis_, and Vital has recorded the presence of the adult
stage in man.
In view of the fact that Galli-Valerio was unable to infect himself
experimentally with this species, the specific determination made by
Vital is open to some question. Even assuming that this tapeworm may
develop in man, the presence of the larval stage in rats is of such
little importance as to be negligible.
CYSTICERCUS FASCIOLARIS—TÆNIA TENIÆFORMIS.
[Fig. 22.]
This encysted larval tapeworm is exceedingly common in the liver of rats
and mice, and when swallowed by cats it develops into an adult tapeworm.
[Illustration:
FIG. 22.—Larval stage of _Tænia teniæformis_. Natural size. (After
Leuckart, 1880, 450, fig. 202.)
]
There are two possible points of view in connection with which this
parasite is of indirect interest in public health matters: (1)
Occasionally these encysted parasites are mistaken for lesions of
tuberculosis; (2) Krabbe (1880) relates that in Jutland there exists a
folk custom of eating chopped raw mice in case of retention of urine,
and in this connection the point has been raised that the possibility is
not excluded that such action might eventually give rise to infection of
man by the parasite in question. No case of such infection in man is as
yet established.
HYMENOLEPIS MURINA[Y] (Dujardin, 1845) = HYMENOLEPIS NANA FRATERNA[Y]
Stiles, 1906.
Footnote Y:
SYNONYM.—_Tænia murina_ Dujardin, 1845 (not Gmelin, 1790).
[Figs. 23 and 24.]
Under the name _Tænia murina_, Dujardin (1845) described for rats a
tapeworm which has been identified by a number of authors (including
Stiles) as identical with the dwarf tapeworm (_Hymenolepis nana_) of
man. If this identification be correct, the rats must be considered as
the great disseminators of this tapeworm. Serious doubts have been
raised, however, as to whether the tapeworm in man is not in reality
distinct from that of the rat, and the evidence in favor of such
conclusion is accumulating. Some slight differences between the two
forms have been noticed, but by some authors these differences have been
considered insufficient to hold the two worms apart. Looss has tried to
infect rats with the dwarf tapeworm found in man in Egypt, but his
results have been negative. Here in Washington Stiles has repeatedly
attempted to infect rats with the dwarf tapeworm found in man in the
United States, but thus far no positive infection has occurred in the
rodents. In Italy, Grassi attempted to transmit the rat form to six
persons, and in one case he found tapeworms, but in view of the
frequency of _H. nana_ in Italy the significance of this one instance
has been questioned; Grassi was not successful in trying to infect rats
with _H. nana_ of man.
[Illustration:
FIG. 23.—Longitudinal section of the intestinal villus of a rat,
containing cystic stage of dwarf tapeworm. Enlarged. (After Grassi &
Rovelli, 1892a, pl. 3, fig. 25.)
]
[Illustration:
FIG. 24.—Adult dwarf tapeworm (_Hymenolepis nana_) of man. Enlarged.
(After Leuckart, 1863, p. 393, fig. 112.)
]
Thus at present the evidence is to the effect that rats and mice are not
to be viewed as the source or reservoir for the dwarf tapeworm (_H.
nana_) of man.
HYMENOLEPIS DIMINUTA[Z] (Rudolphi, 1819) R. Blanchard, 1891.
Footnote Z:
SYNONYMS.—_Tænia diminuta_ Rudolphi, 1819; _T. leptocephala_ Creplin,
1825; _Hymenolepis flavopunctata_ Weinland, 1858; _Tænia (Hymenolepis)
flavopunctata_ Weinland, 1859; _H. (Lepidotrias) flavopunctata_
Weinland, 1861; _T. flavomaculata_ Leuckart, 1863; _T. “flavopuncta”_
Cobbold, 1864 (misprint); _T. “flaviopunctata”_ Vogt, 1878 (misprint);
_T. “flavopunktata”_ Stein, 1882; _T. varesina_ E. Parona, 1884; _T.
minima_ Grassi, 1886; _T. “septocephala”_ Perroncito and Airoldi, 1888
(misprint); _Hymenolepis diminuta_ (Rudolphi, 1819) Blanchard, 1891;
_“Hymenolepsis” flavopunctata_ of Osler, 1895, and other authors
(misprint); _T. “varerina”_ Huber, 1896 (misprint for _T. varesina_);
_T. “flavapunctata”_ Simon, 1896 (misprint); _T. “leptocefala”_
Previtera, 1900; _T. “ceptocephala”_ Lussana and Romaro [? date]
(misprint); _Tenia flavopunctata_ (Weinland, 1858) Packard, 1900.
[Figs. 25 to 30.]
[Illustration:
FIG. 25.—Strobila of _Hymenolepis diminuta_. Natural size. (After
Grassi, 1881, pl. 11, fig. 1.)
]
[Illustration:
FIG. 26.—Head and anterior portion of _H. diminuta_ from the rat.
Enlarged. (After Zschokke, 1889, pl. 1, fig. 21.)
]
SPECIFIC DIAGNOSIS.—_Hymenolepis_: Strobila 10 to 60 millimeters in
length, 2.5 to 4 millimeters in maximum breadth; composed of 800 to
1,300 segments. Head small, almost globular; 200 to 600μ in width;
rostellum rudimentary, pyriform, only slightly protractile; hooks
absent; suckers globular, near the apical portion of the head, 80 to
160μ in diameter. Neck usually short. Segments throughout strobila
broader than long. Genital pores on left margin, near the junction of
the anterior and middle thirds of each segment. Three testes in each
segment; vas deferens dilates into a prominent seminal vesicle before
entering the cirrus pouch, within which also is a vesicle. Gravid
uterus occupies most of the proglottids; its cavity is subdivided into
a large number of incompletely separated compartments filled with
eggs. Eggs round or slightly oval; outer membrane 54 to 86μ in
diameter, yellowish in color, may be radially striated; inner membrane
24 by 20μ to 40 by 35μ in diameter, with mammillate projection at each
pole often not apparent; between outer and inner membranes a prominent
third layer of albuminous substance, often appearing as two delicate
smooth membranes, with intervening space filled by a granular
coagulum; embryonal hooks 11 to 16μ in length.
[Illustration:
FIG. 27.—Male and female organs of _H. diminuta_: _c. p._, cirrus
pouch; _g. p._, genital pore; _ov._, ovary; _rec. sem._,
receptaculum seminis; _s. g._, shell gland; _t._, testiculæ; _ut._,
uterus; _vag._, vagina; _v. def._, vas deferens; _v. ef._, vas
efferens; _ves. sem._, vesicula seminalis; _y. g._, yolk gland.
Enlarged. (After Zschokke, 1889, pl. 2, fig. 22.)
]
[Illustration:
FIG. 28.—Gravid segment of _H. diminuta_. Enlarged. (After Grassi,
1881, pl. 11, fig. 15.)
]
[Illustration:
FIG. 29.—Egg of _H. diminuta_ from man. Greatly enlarged. (After
Bizzozero, 1889a, pl. 4, fig. g″.)
]
HABITAT.—Adults in small intestine of brown or Norway rat (_Mus
decumanus_), black rat (_M. rattus_), house mouse (_M. musculus_),
Egyptian or roof rat (_M. rattus alexandrinus_), wood or field mouse
(_M. sylvaticus_), _Rhipidomys pyrrhorhinus_ [according to Linstow,
1878a, 23], and man (_Homo sapiens_).
DEVELOPMENT.—The larval stage (_Cercocystis H. diminutæ_) occurs in
larval and adult meal moths (_Asopia farinalis_); in young and adult
earwigs (_Anisolabis annulipes_); and in adult beetles (_Acis spinosa_
and _Scaurus striatus_).
GEOGRAPHIC DISTRIBUTION.—Massachusetts, Pennsylvania, Nebraska, Iowa,
District of Columbia, Maryland, Brazil, Italy, Germany, France,
Austria.
This parasite is certainly more common in man in this country than has
heretofore been assumed, but fortunately it seems to be one of the most
harmless and most easily expelled tapeworms occurring in man.
[Illustration:
FIG. 30.—Encysted cystic stage of _H. diminuta_: _caud._, caudal
appendage; _cyst._, adventitious capsule inclosing the cercocystis.
Enlarged. (After Grassi & Rovelli, 1892a, pl. 4, fig. 1.)
]
From present evidence, the rats and mice are looked upon as the regular
hosts for this worm, and hence as the natural reservoir of the
infection. The intermediate host becomes infected from the rodents and
then transmits the infection to man.
It might be mentioned that as yet no extensive study has been conducted
in the United States to differentiate clearly the various species of
_Hymenolepis_ found in our rats and mice. The possibility is therefore
not entirely excluded that some of our cases of _Hymenolepis diminuta_
may eventually be shown to be referable to other species of the same
genus.
NEMATODA—TRUE ROUND WORMS.
Family TRICHINELLIDÆ.[AA]
Footnote AA:
SYNONYM.—_Trichotrachelidæ._ It becomes necessary under the
international code to change the family name; the family name
_Trichinellidæ_ is chosen as less likely to lead to confusion than a
family name based upon _Trichuris_.
FAMILY DIAGNOSIS.—_Nematoda_: Elongate cylindrical worms; cephalic
portion long and very slender, caudal portion more or less swollen.
Mouth rounded, without lips. Esophagus relatively very long, composed
of a single row of large cells, forming the so-called “cell body” and
supporting a narrow esophageal tube; anus terminal or nearly so.
Male: With a single spicule or without spicule.
Female: With one ovary; vulva near caudal end of cell body, close to
point where body increases in diameter; oviparous or viviparous.
Eggs: Oviparous species, with thick shell, with opening at each pole,
closed by a transparent plug.
TYPE GENUS.—_Trichinella_ Railliet, 1895.
This family furnishes two parasites to man: The whipworm (_Trichuris
trichiura_) of the colon, and the trichina or flesh worm (_Trichinella
spiralis_, see p. 101).
Genus TRICHINELLA[AB] Railliet, 1895.
Footnote AB:
SYNONYMS.—_Trichina_ Owen, 1835 [not Meig., 1830, insect.];
_Trichinus_ Fraser, 1881a, for _Trichina_.
GENERIC DIAGNOSIS.—_Trichinellidæ_: Very minute worms, of nearly
uniform diameter. Adults in intestine of mammals, larvæ encysted in
muscles.
Male: Without spicules, but with 2 conical appendages on the tail, at
side of terminal cloacal opening.
Female: Vulva about one-fifth the length from anterior end;
viviparous.
TYPE SPECIES.—_Trichinella spiralis_ (Owen, 1835) Railliet, 1895.
TRICHINELLA SPIRALIS (Owen, 1835) Railliet, 1895.
[Figs. 31 to 51.]
SPECIFIC DIAGNOSIS.—_Trichinella_: Body thread-like, visible to naked
eye.
Male: Length, 1.4 to 1.6 millimeters; diameter, 40μ; distal of cloacal
opening, 2 pairs of papillæ, the anterior pair hemispherical,
posterior pair conical.
Female: Length, 3 to 4 millimeters; diameter, 60μ; anus terminal;
vulva one-fifth of length of body from the mouth; viviparous.
HABITAT.—Adults in lumen and wall of small intestine, encysted larvæ
in muscles of various mammals, particularly in rats, mice, swine, and
man.
GEOGRAPHIC DISTRIBUTION.—More or less cosmopolitan.
SOURCE OF INFECTION.—From the life cycle of this parasite it is clear
that the permanent reservoir of infection must be some animal with
cannibalistic tendencies. Of the three most important hosts (man, swine,
and rats), the rats present ideal conditions in this respect. It is true
that there are some tribes of man which are cannibalistic, but their
distribution is restricted. Likewise swine are in so far cannibalistic
that they eat uncooked swine offal and swill, but this is due to the
shortsightedness of man rather than to the habits of the swine.
Accordingly, neither man nor the hog presents the proper theoretical
conditions for the perpetuation of the parasites and hence to serve as
reservoir for the disease it causes.
Rats, on the contrary, are cannibalistic, and trichinosis is a common
disease among them. Hence they may be viewed as the natural reservoir
for the parasites and for the disease it causes; hence, also, any
well-directed public health campaign against trichinosis should consider
the eradication of rats.
Rats become infected by eating each other; by eating scraps of pork
found on the offal pile of slaughterhouses, or in swill; and by eating
scraps of human flesh in dissecting rooms of medical schools.
[Illustration:
FIG. 31.—Female trichina from the intestine; 24 hours after infection.
Enlarged. (After Leuckart, 1866a, pl. 1, fig. 1.)
]
Swine become infected by eating rats, and by eating scraps of pork on
the offal pile of slaughterhouses, or in swill.
Man becomes infected almost exclusively by eating pork and boar meat.
The rare infections which occur from eating other meat are almost
negligible.
MEDICAL SIGNIFICANCE.—_Trichiniasis_ or _trichinosis_ refers to
infection with the trichina or flesh worm. Normally it occurs only in
mammals, chiefly carnivorous and omnivorous species, and it is
transmissible from any infected mammal to any other mammal susceptible
to it, in case the latter eats the uncooked flesh of the former.
_Symptoms._—In heavy infections there may be three more or less distinct
periods of the disease, corresponding to the three stages in the life
cycle of the parasite; but these stages are obscure in light or in
repeated infections. Profuse sweating may last during the entire attack.
[Illustration:
FIG. 32.—Gravid adult female trichina. Enlarged. (After Leuckart,
1866a, pl. 1, fig. 2.)
FIG. 33.—Adult male trichina from the intestine. Enlarged. (After
Leuckart, 1866a, pl. 1, fig. 5.)
FIG. 34.—External genitalia of same. Enlarged. (After Leuckart, 1866a,
pl. 1, fig. 7.)
FIG. 35.—The same with extruded cloaca. Enlarged. (After Leuckart,
1866a, pl. 1, fig. 8.)
FIG. 36.—Cephalic portion of a trichina showing central nervous system
and anterior portion of intestinal canal. Greatly enlarged. (After
Leuckart, 1866a, pl. 1, fig. 13.)
FIG. 37.—Transverse section of a female trichina. Greatly enlarged.
(After Leuckart, 1866a, pl. 1, fig. 16.)
FIG. 38.—Young trichina embryo in a muscle fibre. Greatly enlarged.
(After Leuckart, 1866a, pl. 2, fig. 1.)
]
Period of ingression: The adult parasites are in the intestine, hence
gastro-intestinal symptoms develop; irregular appetite, nausea, diarrhea
or constipation, colicky pains; a temporary edema around eyes about the
eighth day; muscular pains begin.
Period of digression: This begins about the eighth to the fifteenth day,
sometimes later; young embryos are wandering to and attacking the
muscles, hence muscular symptoms (myositis) develop; painful tension of
muscles, especially biceps; members assume semiflexed position;
movements, chewing, swallowing, breathing, and speech become difficult;
eyes become fixed; fever.
[Illustration:
FIGS. 39–42.—Later stages of same; the muscular structure is
undergoing changes. (After Leuckart, 1866a, pl. 2, figs. 3, 6, 7,
8.)
FIGS. 43–45.—Muscle trichinæ, 0.3 mm., 0.4 mm., and 0.6 mm. long.
(After Leuckart, 1866a, pl. 2, figs. 10–12.)
]
Period of regression: The parasites become encysted in muscles. All
symptoms may increase, then gradually decrease; cachexia and anemia
resulting from malnutrition; pruritis, miliary cutaneous eruptions;
desquamation; about twenty-fourth day, a “second” edema develops,
especially about the face; lungs may become edematous; bronchial
catarrh, pneumonia, or pleurisy may appear; gradual recovery.
[Illustration:
FIG. 46.—A female trichina from the muscle. Greatly enlarged. (After
Leuckart, 1866a, pl. 1, fig. 12.)
]
[Illustration:
FIG. 47.—A piece of pork with encysted trichinæ. Enlarged. (After
Braun, 1903, p. 251, fig. 195.)
]
_Lethality._—The lethality varies from 0 to 100 per cent; it averaged
5.6 per cent in 14,820 cases collected from literature; it is dependent
upon amount of infection which remains in the body; low before second
and after seventh week, highest from fourth to sixth week.
_Prognosis._—Better in cases having severe diarrhea in first stage.
_Complications and sequelæ._—Abortion, menstrual disturbances,
pneumonia, pleurisy, peritonitis.
[Illustration:
FIG. 48.—Section through a rat’s muscle; the infected muscle fiber has
lost its striation, its nuclei are enlarged and increased in number.
Greatly enlarged. (After Hertwig-Graham, see Braun, 1903, p. 284,
fig. 212B.)
FIG. 49.—Portion of an isolated trichina cyst, at the pole of which
connective tissue cells have wandered into the thickened sarcolemma.
Greatly enlarged. (After Hertwig-Graham, see Braun, 1903, p. 284,
fig. 212C.)
]
_Clinical diagnosis._—Make microscopic examination:
(1) Of pork, if any has been left, to find encysted larvæ; if larvæ are
found, feed pork immediately to two or three guinea pigs or _white_
rats, to determine if the encysted larvæ are alive; kill one rat after
three days and examine intestinal content for adult; kill the second rat
after two weeks, the third rat after three weeks, and hunt for larvæ in
muscular portion of diaphragm. Even if live trichinæ are found in
intestine, an examination of the muscles may show that the worms were
too weak to reproduce, hence prognosis is favorable.
(2) Of patient’s blood, for increased proportion of eosinophiles.
(3) Of patient’s stools, for discharged adult worms, especially if
diarrhea is severe; dilute the fecal matter with warm water and pour off
whatever floats; place remainder in a shallow glass dish so that it will
not be over one-twelfth of an inch deep; move the dish gently around
over a dark background (such as dark paper), and hunt for small
hair-like objects; place these, if found, in a drop of water on a slide,
cover with a cover slip, and examine under low power. Or, if necessary,
make a microscopic examination.
(4) Of small excised portion of patient’s deltoid, about three to four
weeks after infection, for encysted larvæ; cut a small piece parallel to
muscle fibers, tease this on a slide, add a drop of pure water, or water
and glycerine, cover with another slide, flatten gently by pressure
while examining under low power.
[Illustration:
FIG. 50.—Calcified trichinæ in uncalcified cysts, from pork. Enlarged.
(After Ostertag, see Braun, 1903, p. 285, fig. 213.)
]
Suspect trichinosis especially under following circumstances: Several
patients in same family or in same neighborhood, usually of North German
descent, show typhoid-like symptoms shortly after a celebration
(wedding, birthday party, etc.) at which pork was served.
[Illustration:
FIG. 51.—Three phases of calcification of trichinæ and their cysts,
the changes starting from the poles of the cysts. Enlarged. (After
Ostertag, see Braun, 1903, p. 285, fig. 214.)
]
_Differential diagnosis._—Consider especially typhoid fever and
rheumatism.
_Treatment._—Purge in early stage to carry away the adult worms and thus
eventually decrease the amount of muscular infection. No treatment is
known which can be relied upon to kill the larvæ in the muscles; benzine
has been suggested. Stimulants may be given to carry patients through
until the larvæ encyst.
PROPHYLAXIS.—_Kill off rats and mice._—Educate public to eat pork only
when thoroughly cooked or thoroughly cured. A practical test of cooking
is the white color of the meat on being cut; if the cut surface is
reddish and serous, the pork is not sufficiently cooked to kill
trichinæ.
As a matter of practical experience, the microscopic inspection of pork
has not given the protection it is generally supposed to give. Of 6,329
cases with 318 deaths reported for Germany during the years 1881–1898,
3,388 cases with 132 deaths are directly attributable to faults in the
inspection. This system directly increases the tendency to eat raw pork,
gives the public a false sense of security, and does not give practical
results commensurate with its expense.
ACANTHOCEPHALA—THORN-HEADED WORMS.
Genus GIGANTORHYNCHUS Hamann, 1892.
GENERIC DIAGNOSIS.—_Acanthocephala, Gigantorhynchidæ_: Large worms
with annulate round to flat, tape-like body. Hooks with 2 roots and
completely covered with transparent chitin. Proboscis sheath a
muscular apparatus, without cavity. Central nervous system caudad of
equator of proboscis sheath and eccentric. Lemnisci long, cylindrical,
with central canal.
TYPE SPECIES.—_Gigantorhynchus echinodiscus_ (Diesing, 1851).
The Moniliform Thorn-headed Worm—GIGANTORHYNCHUS MONILIFORMIS
(Bremser, 1819).
[Figs. 52 to 58.]
SPECIFIC DIAGNOSIS.—_Gigantorhynchus_ (p. 108): Body attenuated
anteriorly, with fine transverse striæ or rings, or even constrictions
which give the appearance of a series of beads, except in the caudal
fourth of body, which is nearly smooth and cylindrical. Proboscis 425
to 450μ long, 176 to 190μ in diameter, armed with feeble, very curved,
26μ long, hooks arranged more or less in quincunx and forming at most
15 transverse and about 12 longitudinal rows. Lemnisci more than a
centimeter in length, cylindrical, undulated posteriorly.
Male: Length 4 to 4.5 centimeters long; bursa campaniform.
Female: Length 7 to 8 centimeters (to 27 centimeters after Westrumb).
Eggs: Ellipsoidal, 85 by 45μ; external envelope thin, yellowish;
middle envelope very thick, colorless, homogeneous; inner envelope
less thick, colorless, and quite pliant. Embryo striated transversely
in posterior two-thirds, and covered with spines which increase in
size toward anterior end of embryo, the anterior spines being
transformed into hooklets with prong and base.
Development: With beetles (_Blaps mucronata_) as intermediate host.
HABITAT.—Small intestine of various small mammals; brown rat (_Mus
decumanus_); white rat (_Mus norvegicus albus_); _M. fuscirostris_;
hamster (_Cricetus frumentarius_); dormice (_Myoxus quercinus_ or
_glis_); field mole (_Arvicola arvalis_ or _agrestris_?); _Lemnus
arvalis_; and _Mustela putorius_. It can also develop in man, as has
been shown experimentally by Grassi and Calandruccio (1888, 521–525).
MEDICAL SIGNIFICANCE.—Grassi and Calandruccio report a doubtful case of
infection in a girl near Catania. Calandruccio infected himself
experimentally by swallowing the young worms taken from a Blaps. Twenty
days later he was seized with severe pains which increased on pressure;
diarrhea followed, with ringing in the ears, fatigue, and somnolence.
Seventeen days later the characteristic eggs were found in his stools,
and twelve days later the symptoms became so severe that he took 8 grams
of extract of male fern; one to two hours later he passed 53 of the
parasites. For two days the symptoms continued, on the second day fever
developed, but all symptoms disappeared on the third day.
[Illustration:
FIG. 52.—_Gigantorhynchus moniliformis_, female. ×2. (After Grassi &
Calandruccio, 1888, p. 523, fig. 1.)
FIG. 53.—_G. moniliformis_, male. ×2. (After Grassi & Calandruccio,
1888, p. 523, fig. 2.)
FIG. 54.—Rostellum of _G. moniliformis_. Greatly enlarged. (After
Grassi & Calandruccio, 1888,
p. 523, fig. 3.)
FIG. 55.—Hooks from same. Greatly enlarged. (After Grassi &
Calandruccio, 1888, p. 523, fig. 4.)
FIG. 56.—Eggs of _G. moniliformis_, with embryo. Greatly enlarged.
(After Grassi & Calandruccio,
1888, p. 523, fig. 5.)
FIG. 57.—Egg very greatly enlarged. (After Grassi & Calandruccio,
1888, p. 524, fig. 6.)
FIG. 58.—A young larva of _G. moniliformis_ in a _Blaps_; the
rostellum is invaginated and the larva is
surrounded by a thick inner jelly-like and thin outer cuticular
covering. Enlarged. (After Grassi &
Calandruccio, 1888, p. 524, fig. 7.)
]
ARACHNOIDEA.
Genus LINGUATULA Frœhlich, 1789.—Tongue worms.
Species LINGUATULA SERRATA Frœhlich, 1789.
The larva of this parasite is found encysted in the entrails of rabbits,
cattle, and certain other animals, and it becomes mature in the nasal
cavities of canines.
Both the larva and the adult have been reported for man, and the larva
has been reported as occurring in _Mus decumanus_.
As canines are not fond of eating rats, the presence of the larval
tongue worm in the latter is of more academic interest than practical
importance, and although the theoretical possibility must be admitted
that a dog by eating rats might become infected with tongue worms and
eventually might transmit the infection to man, these possibilities seem
somewhat remote. Remote possibilities must also be admitted to the
effect that if a person ate a rat infected with tongue worms this person
might become infected.
COMPENDIUM OF ANIMAL PARASITES REPORTED FOR RATS AND MICE (GENUS MUS).
By CH. WARDELL STILES, Ph. D., _Public Health and Marine-Hospital
Service_,
and
ALBERT HASSALL, M. R. C. V. S., _Assistant, Division of Zoology, United
States Bureau of Animal Industry_.
The following list of parasites is prepared from the detailed host
catalogues of the zoological divisions of the Public Health and
Marine-Hospital Service and the Bureau of Animal Industry.
The species of hosts and parasites are taken as given by the various
authors. It is needless to say that no list of this kind can ever lay
claim to being complete.
Genus MUS Linneaus, 1758.
[_Mus musculus_ should be the type species.]
MUS AGRARIUS.—Harvest Mouse.
CESTODA:
_murina_ Dujardin: Hymenolepis.—Small intestine. [See fraterna.]
NEMATODA:
_obvelata_: Oxyuris.—Intestine.
ARACHNOIDEA:
_acuminatus_ Neumann: Ixodes.—External.
INSECTA:
_fasciatus_ Bosc: Ceratophyllus.—External.
_musculi_ Dugès: Ctenopsyllus, Ctenopsylla.—External.
MUS ALBIPES.
INSECTA:
_pallidus_ Taschenberg: Pulex.—External.
MUS ALEXANDRINUS.—Roof Rat.
[See also _Mus rattus alexandrinus_.]
CESTODA:
_diminuta_ Rudolphi, 1819: Tænia, Hymenolepis.—Small intestine.
_fasciolaris_ Rudolphi: Cysticercus.—Liver.
_leptocephala_: Tænia.—Small intestine.
_murina_ Dujardin: Hymenolepis.—Small intestine. [See fraterna.]
MUS ALEXANDRINUS ALBIVENTRIS.
CESTODA:
_diminuta_ Rudolphi: Hymenolepis.—Small intestine.
MUS AMPHIBIUS.
_Dubium_ Rudolphi.—Inguinal gland.
CESTODA:
_fasciolaris_ Rudolphi: Cysticercus.—Liver.
_omphalodes_ Hermann: Tænia, Anoplocephala.—Intestine.
NEMATODA:
_nodosus_: Trichocephalus.—Cecum.
_obvelata_: Ascaris.
MUS ARVALIS.
CESTODA:
_fasciolaris_ Rudolphi: Cysticercus.—Liver.
_longicollis_: Cysticercus.
_omphalodes_ Hermann: Tænia, Anoplocephala.—Intestine.
NEMATODA:
_nodosus_: Trichocephalus.
_obvelata_: Ascaris.
ACANTHOCEPHALA:
_moniliformis_: Echinorhynchus.
MUS BARBARUS.
[See also _barbatus_ Enderl.]
INSECTA:
_spiculifer_ Gerv.: Hæmatopinus, Polyplax.—External.
MUS BRASILIENSIS Geoffr.
[See also _Holochilus brasiliensis_.]
CESTODA:
_pisiformis_ Zeder: Cysticercus.
NEMATODA:
_muris brasiliensis_ Diesing: Physaloptera.
_obvelata_ Bremser: Oxyuris.
MUS CAPENSIS.
CESTODA:
_muris capensis_: Tænia.—Intestine.
NEMATODA:
_contortus_ Rudolphi: Trichocephalus.—Cecum.
MUS CRICETUS.
CESTODA:
_straminea_ Gœze: Tænia.—Intestine.
MUS DECUMANUS Pallas.—Brown or Norway Rat; German Wanderratte.
PROTOZOA:
? _balfouri_: Hæmogregarina.—Blood.
_intestinalis_ Lambl, 1859: Lamblia.—Intestine. [See duodenalis.]
_lewisi_ Saville-Kent: Herpetomonas, Trichomonas, Trypanosoma.—Blood.
species Siebold: Sarcocystis.—Muscles.
TREMATODA:
_armata_: Cercaria.
_muris_: Distomum.
_spiculator_ Dujardin, 1845: Distoma, Echinostoma, Distomum,
Echinostomum.—Small intestine.
CESTODA:
_brachydera_ Diesing: Tænia.—Small intestine.
_contracta_ Janicki: Hymenolepis.—Intestine.
_crassa_ Janicki: Hymenolepis.—Intestine.
_diminuta_ Rudolphi: Tænia, Hymenolepis.—Small intestine.
_fasciolaris_ Rudolphi: Cysticercus.—Liver.
_horrida_ Linstow, 1901: Tænia, Hymenolepis.—Intestine.
_microstoma_ Dujardin: Tænia, Hymenolepis.—Small intestine.
_murina_ Dujardin, 1845: Tænia, Hymenolepis.—Small intestine. [See
fraterna.]
_nana_ Siebold: Hymenolepis.—Small intestine. [See fraterna, murina.]
_pusilla_ Gœze: Tænia, Catenotænia.—Small intestine.
_ratti_: Tænia.—Intestine.
_relicta_ Zschokke, 1888: Tænia, Hymenolepis.—Small intestine.
species Janicki: Hymenolepis.
species: Hymenolepis.—Small intestine.
NEMATODA:
_annulosum_ Dujardin: Trichosoma, Trichosomum, Calodium.—Duodenum,
small intestine.
_anulosum_ see annulosum Dujardin: Trichosoma.
_circumflexa_ Polonio: Trichina.—Encysted in peritoneum.
_crassicauda_ Bellingham, 1840: Trichodes, Trichosoma.—Urinary
bladder, ureter, kidneys, intestine.
_hepaticum_ Bauer: Trichosoma.—Liver.
_hepaticum_ Railliet, 1891: Trichosoma.—Liver.
_hepaticus_ Bancroft: Trichocephalus.—Liver.
_longus_ Grassi & Segrè: Strongyloides, Rhabdonema.—Intestine.
_minimum_ Molin: Gongylonema.
_murina_ Leuckart: Spiroptera.—Stomach. [See obtusa.]
_muris_ Gmelin: Filaria.—Stomach.
_obtusa_ Rudolphi: Filaria, Spiroptera.—Stomach. [See murina.]
_obvelata_ Bremser: Oxyuris.—Large intestine.
_papillosum_ Polonio: Trichosoma.—Urinary bladder.
_rhytipleuritis_ Deslongchamps: Filaria.—Stomach.
_schmidtii_ Linstow: Trichosoma.—Urinary bladder.
species Davaine: Filaria [embryo].—Blood.
species: Heterakis.—Large intestine.
species undetermined: Oxyuris.
species Gerstæcker: Spiroptera.—Encapsuled in wall of stomach and
intestine.
species Bakody: Spiroptera.—Encapsuled in walls of alimentary canal
and muscles.
species: Spiroptera.—Encapsuled in wall of stomach and intestine.
species Parona: Strongyloides.
species Lutz, 1894: Strongylus.—Small intestine.
? species Railliet: Trichosoma.
_spiralis_ Owen, 1835: Trichina, Trichinella.—Adult in intestine,
larva in muscles.
_spumosa_ Schneider: Heterakis.—Cœcum and large intestine.
? _tenuissimum_ Leidy, 1891: Trichosomum.—Liver. [See hepaticum.]
ACANTHOCEPHALA:
_moniliformis_ Bremser: Echinorhynchus, Gigantorhynchus.
ARACHNOIDEA:
_agilis_ Koch: Lælaps.—External [See echidninus, musculi.]
_alepis_ Railliet & Lucet, 1893: Sarcoptes, Notoedres.—External, ears,
genitalia.
_complanatus_ Kramer: Gamasus.—External. [See stabularis, fenilis.]
_decumani_ Tiraboschi: Myonyssus.
_echidninus_ Berlese: Lælaps.—External.
_ensifera_ Poppe: Myobia.—External.
_fenilis_ Mègnin: Gamasus.—[See stabularis, complanatus.]
_musculi_ Schrank: Pediculus, Myobia.—External, head.
_musculi_ Mègnin: Hæmomyson.—External. [See echidninus, agilis.]
_musculi_ Schrank: Myobia.—External.
_ricinus_ Linné: Acarus, Ixodes.—External. [See rufus, sulcatus,
sciuri.]
_rufus_ Koch: Ixodes.—External. [See ricinus.]
_sciuri_ Koch: Ixodes.—External. [See ricinus.]
sp. n. Banks: Lælaps.—External.
_stabularis_ Koch: Gamasus, Hypoaspis, Lælaps.—External. [See
complanatus, fenilis.]
_sulcatus_ Koch: Ixodes.—External. [See ricinus.]
_tænioides_ Lamark (larva): Linguatula. [See serrata.]
INSECTA:
_acanthopus_ Denny: Hæmatopinus, Hoplopleura.—External.
_bidentatiformis_ Wagner: Neopsylla.—External.
_brasiliensis_ Baker: Pulex.—External.
_canis_ Curtis: Ctenocephalus, Ceratophyllus.—External.
_cheopis_ Roth.: Pulex, Læmopsylla.—External.
_consimilis_ Wagner: Ceratophyllus.—External.
_fasciatus_ Bosc: Pulex, Ceratophyllus. External.
_felis_ Bouché: Ctenocephalus.—External.
_irritans_ Linné: Pulex.—External.
_lagomys_ Wagner: Ceratophyllus.—External.
_londiniensis_ Roth.: Ceratophyllus.—External.
_musculi_ Dugès: Ctenopsylla.—External.
_mustelæ_ Wagner: Ceratophyllus.—External.
_penicilliger_ Grube: Ceratophyllus.—External.
_philippinensis_ Herzog: Pulex.—External.
_serraticeps_ Gervais: Pulex.—External.
_spinulosus_ Burmeister: Hæmatopinus, Polyplax.—External.
MUS DECUMANUS × MUS NORVEGICUS ALBUS.
PROTOZOA:
undetermined.—Small intestine.
CESTODA:
_fasciolaris_: Cysticercus.—Liver.
species: Hymenolepis.—Intestine.
NEMATODA:
_spiralis_ Owen: Trichinella.—Artificial infection.
MUS DOMESTICUS = MUS MUSCULUS ALBUS.
ARACHNOIDEA:
_crotali_ Humboldt (larva): Porocephalus.—Encysted in various organs,
experimental.
MUS FERCULINUS.
INSECTA:
_thomasi_ Rothschild: Stephanocircus.—External.
MUS FLAVIDUS.
CESTODA:
? _gracilis_ Janicki: Davainea.—Intestine.
MUS FULIGINOSUS.
ARACHNOIDEA:
_crotali_ Humboldt: Porocephalus.—Encysted in various organs.
MUS FURCIROSTRIS Wagner.
ACANTHOCEPHALA:
_moniliformis_ Bremser: Echinorhynchus.—Intestine.
MUS GENTILIS.
INSECTA:
_cheopis_ Rothschild: Pulex.—External.
MUS LEMMUS.
CESTODA:
_lemmi_: Tænia.—Intestine. [See muris lemmi.]
_muris lemmi_: Tænia.—Intestine. [See lemmi.]
MUS MEYERI.
CESTODA:
_celebensis_ Janicki, 1902: Davainea.—Intestine.
MUS MINIMUS Ptrs.
NEMATODA:
species Linstow, 1901: Spiroptera.—Stomach.
MUS MINUTUS Pallas.—German Zwergmaus.
NEMATODA:
_obvelata_ Bremser: Oxyuris.—Cecum.
_oxyura_ Nitzsch, 1821: Ascaris.—[See obvelata.]
MUS MUSCHENBROCKI.
CESTODA:
_polycalceola_ Janicki: Davainea.—Intestine.
MUS MUSCULUS[AC] Linné, 1758.—House Mouse.
Footnote AC:
In laboratory experiments the white mouse is used more than the
ordinary form, but the host is frequently reported simply as “the
mouse.”
——:
_Dubium_ Rudolphi, 1819.—Inguinal gland.
PROTOZOA:
_brucei_: Trypanosoma, Trypanozoon.—Blood, artificial infection.
_dimorphon_: Trypanosoma, Trypanozoon.—Blood.
_duttoni_ Thiroux, 1905: Trypanosoma, Trypanozoon.—Blood.
_equinum_: Trypanosoma, Trypanozoon.—Blood, artificial infection.
_equiperdum_: Trypanosoma, Trypanozoon.—Blood, artificial infection.
_evansi_: Trypansoma, Trypanozoon.—Blood, artificial infection.
_falciforme_ Schneider: Coccidium, Eimeria.—Intestine.
flagellate, something like Herpetomonas bütschlii.
_gambiense_: Trypanosoma, Trypanozoon.—Blood, artificial infection.
_intestinalis_ Lambl, 1859: Lamblia, Megastoma.—Intestine. [See
duodenalis, muris.]
_muris_ Grassi: Amœba.
_muris_ Bensen, 1908: Lamblia.—Intestine. [See intestinalis.]
_muris_ Schuberg: Coccidium.—Intestine.
_muris_ Smith & Johnson, 1902a: Klossiella.—Renal epithelium.
_muris_ Balfour: Leucocytozoon.—Blood.
_muris_ R. Blanchard: Miescheria, Sarcocystis.—Striated muscle.
_musculi_ Kendall: Trypanosoma.—Blood.
_schubergi_ Labbé: Pfeifferella.—Intestine.
species Th. Smith: Eimeria.—Kidney.
species J. J. Clarke: Pfeifferella.—Intestine.
species Miescher: Sarcocystis.—Muscles.
_stercorea_ Cienkowski: Chlamydophrys.—Intestine.
TREMATODA:
_armata_: Cercaria.
_muris_ Ercolani, 1882: Distomum.
_musculi_ Rudolphi, 1819: Distoma, Distomum.—Intestine.
_recurvum_ Dujardin, 1845: Distoma, Distomum.—Intestine.
CESTODA:
_canis lagopodis_ Viborg: Tænia.—Intestine. [See lineata.]
_contracta_ Janicki: Hymenolepis.—Intestine.
_crassa_ Janicki, 1904: Hymenolepis.—Intestine.
_diminuta_ Rudolphi: Tænia, Hymenolepis.—Intestine.
_echinococcus._ [See Devé, 1904, October 28; 264.]
_fasciolaris_ Rudolphi, 1819: Cysticercus.—Liver.
_imbricata_ Diesing: Tænia.—Small intestine.
_leptocephala_ Creplin, 1849: Tænia.—Small intestine.
_lineata_ Gœze: Tænia, Mesocestoides, Ptychophysa. [See canis
lagopodis.]
_microstoma_ Dujardin, 1845: Tænia.—Intestine.
_murina_ Dujardin, 1845: Tænia, Hymenolepis.—Intestine. [See
fraterna.]
_muris capensis_: Tænia.
_muris hepatica_ Rœderer, 1762: Fasciola.—Liver. [See fasciolaris.]
_musculi_ Rudolphi, 1810: Tænia.—Abdominal cavity.
_pisiformis_ Zeder: Cysticercus.—Liver.
_pusilla_ Gœze, 1782: Tænia.—Intestine.
species Janicki: Hymenolepis.—Intestine.
species Merrem, 1781: Fasciola.—Liver. [See fasciolaris.]
_tenella_ Pallas, 1781 pars: Tænia.—Abdominal cavity. [See musculi.]
_umbonata_ Molin, 1858: Tænia.—Intestine.
NEMATODA:
_bacillatum_ Eberth: Trichosoma.—Esophagus.
_hepaticum_ Railliet, 1889: Trichosoma.—Liver.
_minimum_ Molin: Gongylonema.—On stomach, liver.
_muris_ Gmelin: Filaria.
_muris_ Werner: Lumbricus, Ascaris, Fusaria. [See obtusa Frœlich.]
_muris musculi_ Creplin, 1849: Trichosoma.—Large intestine.
_musculi_ Rudolphi: Filaria, Gongylonema.—Abdomen.
_nodosus_ Rudolphi: Trichocephalus.—Intestine, cecum.
_oxyura_ Nitzsch, 1821: Ascaris.—[See obvelata.]
_obvelata_ Rudolphi: Oxyuris.—Cecum.
_obtusa_ Rudolphi: Filaria, Spiroptera.—Stomach.
_obtusa_ Frœlich, 1791: Ascaris.—Stomach. [See muris Werner.]
_quadrialata_ Molin: Spiroptera.—Stomach.
_semilanceolata_ Molin, 1858: Oxyuris.—Cecum. [See tetraptera.]
_spiralis_ Owen, 1835: Trichina, Trichinella.—Adult in intestine,
larva in muscles.
_tetraptera_ Nitzsch: Oxyuris.—Cecum. [See semilanceolata.]
_tricuspis_ Leuckart: Ollulanus.—Muscles.
ACANTHOCEPHALA:
_muris_ Zeder: Echinorhynchus.—Stomach.
ARACHNOIDEA:
_coarctata_ Heyden: Myobia.—External. [See musculi Schrank.]
_musculi_ Oudemans: Demodex.—Hair follicles. [See folliculorum
musculi.]
_musculi_ Schrank: Pediculus, Myobia.—External, head.
_musculinus_ Galli-Valerio: Myocoptes.—External.
_simplex_ Tyrrell: Psorergates.—External.
INSECTA:
_acanthopus_ Burmeister, 1838: Hoplopleura, Hæmatopinus.—External.
_agyrtes_ Heller: Typhlopsylla.—External.
_assimilis_ Taschenberg: Typhlopsylla.—External.
_charlottensis_ Baker: Odontopsyllus.—External.
_fasciatus_ Bosc: Ceratophyllus.—External.
_italicus_ Tiraboschi: Ceratophyllus.—External.
_londiniensis_ Roth.: Ceratophyllus.—External.
_musculi_ Dugès: Ctenopsyllus, Ctenopsylla, Typhlopsylla.—External.
_serratus_ Burm., 1838: Hæmatopinus.—External.
_serraticeps_ Taschenberg: Ctenocephalus.—External.
larva of a dipteron, gen. sp.?
_taschenbergi_ Wagner: Ctenopsyllus.—External.
_tripectinata_ Tiraboschi: Hystrichopsylla.—External.
_walkeri_ Roth.: Ceratophyllus.—External.
MUS MUSCULUS ALBUS.—White Mice.
CESTODA:
_fasciolaris_ Rudolphi: Cysticercus.—Liver.
ARACHNOIDEA:
_crotali_ Humboldt (larva): Porocephalus.—Encysted in various organs.
_proboscideum_: Pentastomum. [See crotali.]
MUS NAVALIS.
NEMATODA:
_labiodentata_ Linstow: Spiroptera.—Intestine.
MUS NORVEGICUS Erxl.—Norway Rat.
[See also _Mus decumanus_.]
PROTOZOA:
_lewisi_: Trypanosoma, Trypanozoon.—Blood.
INSECTA:
_bidentatiformis_ Wagner: Ctenophthalmus.—External.
_brasiliensis_ Baker: Pulex.—External.
_fasciatus_ Bosc: Ceratophyllus.—External.
_italicus_ Tiraboschi: Ceratophyllus.—External.
_murinus_ Tiraboschi: Pulex.—External.
_musculi_ Dugès: Ctenopsyllus.—External.
MUS [NORVEGICUS] ALBUS.—White Rat.
PROTOZOA:
_muris_ Fantham: Piroplasma.—Blood.
_perniciosum_ Miller: Hepatozoon.—Liver, blood.
CESTODA:
_fasciolaris_ Rudolphi: Cysticercus.—Liver.
NEMATODA:
_hepaticum_: Trichosoma.—Liver.
_spiralis_ Owen, 1835: Trichinella.—Adult in intestine, larva in
muscle.
ARACHNOIDEA:
_ensifera_ Poppe: Myobia.
MUS PUMILIS Dujardin.—Little Mouse.
CESTODA:
_murina_ Dujardin, 1845: Tænia, Hymenolepis.—Intestine. [See
fraterna.]
MUS PYRRHORHINUS Neuwied.
[See also _Hesperomys pyrrhorhinus_.]
CESTODA:
_diminuta_: Tænia.—Intestine.
ARACHNOIDEA:
_crotali_ Humboldt: Porocephalus.—Encysted in various organs.
_subcylindricum_: Pentastomum.—Liver.
MUS RAJAH.
CESTODA:
_blanchardi_ Parona: Davainea.
MUS RATTUS Linné.—German Hausratte.
PROTOZOA:
“amibes.”
_intestinalis_ Lambl, 1859: Lamblia.—Intestine. [See duodenalis,
muris.]
_lewisi_ Saville-Kent, 1880: Trypanosoma.—Blood.
species Siebold: Sarcocystis.—Muscles.
TREMATODA:
_spiculator_: Distomum.
CESTODA:
_cellulosæ_ Rudolphi: Cysticercus.—Peritoneum.
_diminuta_ Rudolphi, 1819: Tænia, Hymenolepis.—Small intestine.
_fasciolaris_ Rudolphi: Cysticercus.—Liver.
_microstoma_ Dujardin: Tænia, Hymenolepis.—Small intestine.
_minima_: Tænia. [See diminuta.]
_murina_ Dujardin, 1845: Tænia, Hymenolepis.—Small intestine. [See
fraterna.]
_pusilla_ Gœze, 1782: Tænia, Catenotænia.—Small intestine.
_ratti_ Rudolphi: Tænia.—Small intestine.
_ratticola_ Linstow: Bothriocephalus.—Liver.
species Eber: Tænia.—Intestine.
_umbonata_ Molin: Tænia.—Intestine.
_varesina_ Parona: Tænia.—[See diminuta.]
NEMATODA:
_annulosum_ Dujardin: Trichosoma, Calodium.—Intestine.
_anulosum_: Trichosoma. [See annulosum.]
_brauni_ Linstow: Spiroptera.
_circularis_ Linstow: Physaloptera.—Stomach.
_circumflexa_ Polonio: Trichina.—Encysted in peritoneum.
_nodosus_ Rudolphi: Trichocephalus.—Cecum.
_obvelata_ Bremser: Oxyuris.—Cecum.
_oxyura_ Nitzsch, 1821: Ascaris. [See obvelata.]
_ratti_ Diesing: Spiroptera.—Urinary bladder.
_rhytipleuritis_ Deslongchamps: Filaria.—Stomach.
species Gerstæcker: Spiroptera.—Wall of stomach and intestine.
species Bakody: Spiroptera.—Encapsuled in wall of intestine, muscles.
_spumosa_ Schneider: Heterakis.—Cecum, colon.
ACANTHOCEPHALA:
_moniliformis_ Bremser: Echinorhynchus, Gigantorhynchus.—Intestine.
ARACHNOIDEA:
_ægyptium_ Linné: Acarus, Ixodes, Hyalomma.—External. [See
marginatum.]
_agilis_ Koch: Lælaps.—External. [See echidninus, musculi.]
_alepis_ Railliet & Lucet, 1893; Sarcoptes, Notoedres.—External, ears,
genitalia.
_echidninus_ Berlese: Lælaps.—External. [See agilis, musculi.]
_marginatum_ Koch: Hyalomma.—External. [See ægyptium.]
_muris_ Can., 1894: Notoedres.—External. [See alepis.]
_musculi_ Mègnin: Hæmomyson.—External. [See agilis, echidninus.]
_serratum_: Pentastomum.—Thoracic cavity.
INSECTA:
_brasiliensis_ Baker: Pulex.—External. [See cheopis.]
_cæcata_ Enderlein: Dermatophilus, Rhynchoprion.—External.
_cheopis_ Rothschild, 1903: Lœmopsylla.—External. [See brasiliensis,
murinus, pallidus, philippinensis.]
_fasciatus_: Ceratophyllus.—External.
_gallinacea_ Westwood: Echidnophaga, Argopsylla.—External.
_irritans_ Linné: Pulex.—External.
_italicus_ Tiraboschi: Ceratophyllus. External.
_londiniensis_ Rothschild: Ceratophyllus.—External.
_mexicanus_ Baker: Ctenopsyllus.—External.
_murinus_ Tirab.: Pulex.—External. [See cheopis, pallidus,
brasiliensis, philippinensis.]
_musculi_ Dugès: Ctenopysllus.—External.
_pallidus_ Taschenberg: Pulex.—External. [See brasiliensis, cheopis,
murinus, philippinensis.]
_philippinensis_ Herzog: Pulex.—External. [See brasiliensis, cheopis,
murinus, pallidus.]
_rhynchopsylla_ Tiraboschi: Echidnophaga.—External.
MUS RATTUS ALEXANDRINUS.
[See also _Mus Alexandrinus_.]
INSECTA:
_brasiliensis_ Baker: Pulex.—External.
_cæcata_ End: Dermatophilus.—External.
_canis_ Curtis: Ctenocephalus.—External.
_cheopis_ Roth.: Pulex.—External.
_fasciatus_ Bosc: Ceratophyllus.—External.
_felis_ Bouché: Ctenocephalus.—External.
_gallinacea_ Westwood: Echidnophaga.—External.
_irritans_ Linné: Pulex.—External.
_londiniensis_ Roth.: Ceratophyllus.—External.
_murinus_ Tiraboschi: Pulex.—External.
_musculi_ Dugès: Ctenopsylla.—External.
_philippinensis_ Herzog: Pulex.—External.
_rhynchopsylla_ Tiraboschi: Echidnophaga, Argopsylla.—External.
MUS RUFESCENS Gray.
PROTOZOA:
_lewisi_ Saville-Kent, 1880: Trypanosoma, Trypanozoon.—Blood.
MUS SIPORANUS.
CESTODA:
_blanchardi_ Parona: Davainea.—Intestine.
MUS SURIFER.
NEMATODA:
_muricola_: Spiroptera.—Subcutaneous.
MUS SYLVATICUS Linné.—German Waldmaus.
TREMATODA:
_recurvum_ Dujardin, 1845: Distoma, Distomum, D.
(Brachylaimus).—Intestine.
_vitta_ Dujardin, 1845: Distoma, Distomum, D.
(Brachylaimus).—Intestine.
CESTODA:
_muris sylvatici_ Rudolphi: Tænia.—Intestine.
_pusilla_ Gœze: Tænia.—Intestine.
NEMATODA:
_cristatum_ Rudolphi: Ophiostomum, Rictularia.—Intestine.
_lævis_ Dujardin: Strongylus, Metastrongylus.—Intestine.
_minutus_ Dujardin: Strongylus, Metastrongylus.—Intestine.
_muris sylvatici_ Dujardin: Trichosoma.—Intestine.
_nodosus_ Rudolphi: Trichocephalus.—Intestine, cecum.
_obtusa_ Rudolphi: Spiroptera.
_obvelata_ Bremser: Oxyuris.—Cecum.
_oxyura_ Nitzsch, 1821: Ascaris. [See obvelata.]
_polygyrus_ Dujardin: Strongylus, Metastrongylus.—Intestine.
_spirogyrus_ Leuckart: Strongylus.—Intestine.
_stroma_ Linstow, 1884: Oxyuris.—Intestine.
_tetraptera_ Nitzsch: Oxyuris.—Intestine.
ARACHNOIDEA:
_simplex_ Tyrell: Psorergates.—Skin.
INSECTA:
_agyrtes_ Heller: Ctenophthalmus, Typhlopsylla.—External.
_assimilis_ Taschenberg: Typhlopsylla.—External.
_fasciatus_ Bosc: Ceratophyllus.—External.
_gallinæ_ Schrank: Ceratophyllus.—External.
_italicus_ Tiraboschi: Ceratophyllus.—External.
_londiniensis_ Rothschild: Ceratophyllus.—External.
_musculi_ Dugès: Ctenopsyllus, Ctenopsylla.—External.
_obtusiceps_ Ritsema: Hystrichopsylla.—External.
_pentacanthus_ Rothschild: Neopsylla, Ctenophthalmus.—External.
_poppei_ Wagner: Typhloceras, Typhlocerus.—External.
_proxima_ Wagner: Typhlopsylla, Ctenopthalmus.—External.
_talpæ_ Curtis: Hystrichopsylla.—External.
_taschenbergi_ Wagner: Ctenopsylla.—External.
MUS SYLVESTRIS.
PROTOZOA:
_intestinalis_ Lambl, 1859: Lamblia.—Intestine. [See muris.]
MUS TECTORUM Sari.
CESTODA:
_fasciolaris_: Cysticercus.—Liver.
MUS VARIEGATUS.
CESTODA:
_muris variegati_ Janicki: Hymenolepis.—Intestine.
_trapezoides_ Janicki: Davainea.—Intestine.
MUS VELUTINUS Balser, 1905.
INSECTA:
_dasyuri_ Skuse: Stephanocircus.—External.
_hercules_ Roth.: Macropsylla.—External.
_simpsoni_ Rothschild: Stephanocircus.—External.
_simsoni_. [See simpsoni.]
MUS in the sense of “rats.”
The following parasites are reported either from “rats” or from “_Mus_”
in the sense of “rats:”
PROTOZOA:
_brucei_: Trypanosoma, Trypanozoon.—Blood.
_dimorphon_: Trypanosoma, Trypanozoon.—Blood.
_equiperdum_: Trypanosoma, Trypanozoon.—Blood.
_evansi_: Trypanosoma, Trypanozoon.—Blood.
_evansii_: Trypanosoma. [See evansi.]
_gambiense_: Trypanosoma, Trypanozoon.—Blood, artificial infection.
_intestinale_ R. Blanchard, 1885: Megastoma.—Intestine. [See muris.]
_muris_ Grassi: Amœba.
CESTODA:
_fasciolaris_: Cysticercus.
NEMATODA:
_hepaticum_ Railliet, 1889: Trichosoma.—Liver.
_hepaticus_: Trichocephalus.
species Davaine: Filaria.—Blood.
GORDIACEA:
_Gordius._ By error Cerruti & Camerano (1888b, 6) have interpreted a
title by
Leidy (1879) as meaning that he found _Gordius_ in a rat.
ARACHNOIDEA:
_sanguineus_ Latreille: Rhipicephalus.—External.
INSECTA:
_capitis_ Nitzsch: Pediculus.—External.
_canis_ Curtis: Ctenocephalus.—External.
_præcisus_: Hæmatopinus.—External.
MUS species.
Under various “_Mus_ sp.” entries, the following parasites are
reported:
PROTOZOA:
_gambiense_: Trypanosoma.—Blood, artificial injection.
INSECTA:
_aganippes_ Roth.: Ctenopsylla.—External.
_agyrtes_ Heller: Typhlopsylla.—External.
_colossus_ Roth.: Pygiopsylla.—External.
_ellobius_ Roth.: Ctenopsylla.—External.
_hercules_ Roth.: Macropsylla.—External.
_miacantha_: Polyplax.—Hair.
_pinnatus_ Wagn.: Ceratophyllus.—External.
_præcisus_ Neum., 1902: Hæmatopinus.—External.
WATER RAT.
[See also _Mus amphibius_.]
CESTODA:
_longicollis_: Cysticercus.—Axillary space.
INSECTA:
_spiniger_ Burm., 1838: Hæmatopinus.
MUS.
The following parasites are recorded under “_Mus._:”
PROTOZOA:
_falciformis_: Eimeria.—Intestine.
TREMATODA:
_migrans_: Dist.
CESTODA:
_blanchardi_ Parona: Davainea.
_celebensis_ Janicki: Davainea.
_gracilis_ Janicki: Davainea.
_muris variegati_ Janicki: Hymenolepis.
_nana_ Siebold: Hymenolepis. [See fraterna.]
_polycalceola_ Janicki: Davainea.
_relicta_ Zschokke: Hymenolepis.
_trapezoides_ Janicki: Davainea.
NEMATODA:
_hepaticum_ Railliet: Trichosoma.
_obvelata_ Bremser: Oxyuris.—Intestine.
ARACHNOIDEA:
_musculi_ Oudemans: Demodex.
INSECTA:
_cheopis_ Roth.: Lœmopsylla.—External.
_felis_ Bouché: Ctenocephalus.
MUS.—A Field Mouse.
CESTODA:
_longicollis_: Cysticercus.—Thoracic cavity.
THE FLEA AND ITS RELATION TO PLAGUE.
By Passed Assistant Surgeon CARROLL FOX,
_United States Public Health and Marine-Hospital Service_.
THEORIES AS TO TRANSMISSION OF PLAGUE.
1. Direct contagion from man to man.
2. Through slight abrasions of the skin, mucous membranes of mouth,
tonsils, nose, and conjunctiva receiving contaminated material.
3. Through the respiratory tract, from air contaminated with dried
infectious sputum or dejecta. (Possibly the cause of primary pneumonic
plague.)
4. Through the alimentary tract from food contaminated with saliva or
excretions from plague patients, or dejecta or the feet of insects
that have fed on plague material. In the case of rats, from eating the
carcasses of infected rats.
5. Infected clothes, soil, or houses.
6. Through the bites of insects, especially the flea.
It has been noticed for many years that an epidemic of plague in man
was associated with an epizootic of high mortality among rats, but it
was not until Yersin discovered the _Bacillus pestis_ in 1894 that the
disease in man and rats was shown to be identical. The first five
theories are not satisfactory in explaining the epidemiology of
plague, and in 1897 Simond advanced the theory that plague was carried
by means of fleas. Hankin in 1898 also suggested an insect as an
intermediate host. This theory has been developed by Ashburton
Thompson, Gauthier and Raybaud, Liston, Verjbitski, and others, and
finally by the last Indian Plague Commission, whose work makes a
distinct advance in our knowledge of this subject. The reader is
referred to the work of this commission for a review of the subject,
which has been liberally used in the preparation of this paper.[AD]
Footnote AD:
Journal of Hygiene (Vol. VI, No. 4; Vol. VII, No. 3; Vol. VII, No.
6; Vol. VIII, No. 2).
INSECTS THAT HAVE BEEN SUSPECTED IN THE TRANSMISSION OF PLAGUE.
It is probable that all insects capable of sucking blood will take the
_Bacillus pestis_ into their alimentary canal if they feed on a
septicæmic plague animal. Ogata suggested that not only the flea but
the mosquito also may be responsible for the transmission of plague.
Yersin, Hankin, and Nuttall have each demonstrated the presence of
_Bacillus pestis_ in the dejecta of flies and ants; and Nuttall and
Verjbitski in the stomach and dejecta of the bedbug. Hertzog found the
bacilli in the _Pediculus capitis_ taken from a child which died of
plague, and McCoy[201] has found the organism in lice, _Hæmatopinus
columbianus_, taken from a plague-infected squirrel. The plague
bacilli have been frequently demonstrated in rat fleas taken from
plague rats, and McCoy has shown its presence in the flea
(_Ceratophyllus acutus_) of the California ground squirrel (_Citellus
beecheyi_). The cockroach has also been thought to be instrumental in
spreading the infection by contaminating food. The presence of bacilli
in the stomach and dejecta of insects has not only been proven
microscopically but by animal inoculation as well.
Assuming that the relation between rat plague and human plague has
been proven without a doubt—that is, that an outbreak of human plague
is associated with an infection in rats, or, in other words, that
plague is primarily a disease of rats and secondarily a disease of
man—the theory that it is conveyed through an intermediate parasitic
host is the only one which will fulfill all the requirements, and
after a study of their habits we are able to exclude all of the
parasites but the flea as the active agent in its transmission.
Plague is rarely or never contracted either in rat or in man by eating
contaminated food. Therefore those insects like flies and cockroaches,
which are supposed to spread the infection by contaminating food with
their dejecta, need not be considered.
The habits of the domestic mosquitoes are such that while they
occasionally do bite animals they usually feed on the blood of man,
and are not known to feed where there is much hair, as there is on the
rat. This also applies to the bedbug. Verjbitski has shown
experimentally that bedbugs would not feed on rats until the animals
were shaved.
Pediculi are degenerate insects, their powers of locomotion being
limited. Their eggs are laid on and are attached to the hair of the
host. They are born, live, and die on the same host, and rarely pass
from one animal to another of a different species. It can not be
denied, however, that this parasite occasionally may be instrumental
in spreading plague from rat to rat. The _Pediculus capitis_, if
placed on a rat, will feed with avidity, but these insects are rarely
found upon rats in nature.
We have no record of plague bacilli having been demonstrated in mites
commonly found on rats, but no doubt if search be made they could be
found after feeding on a septicæmic plague rat. These mites, however,
always confine themselves closely to their particular host and are not
known to bite man. The tiny itch mite (_Notoedres alepis_, Railliet
and Lucet) producing rat scabies has, according to Schumann,[202] been
known to cause a cutaneous lesion in man, but this mite need not be
considered from a plague standpoint.
The flea, on the other hand, lives but part of the time on its host,
its eggs developing in the nests or runs of the animal. Again, this
insect does not confine itself to one particular species of host only,
as frequently the flea of one animal is found on an animal of an
entirely different species. Unlike the lice, they are very active and
can readily move from place to place. Not only that, but it has been
frequently demonstrated that the fleas of rats and of other animals
would readily take to man, especially if their natural host was
scarce. That rat fleas will bite man has been demonstrated by Gauthier
and Raybaud, working with the _Leomopsylla cheopis_; Tidswell,
_Lœmopsylla cheopis_ and _Ceratophyllus fasciatus_; Liston,
_Lœmopsylla cheopis_; Tiraboschi, _Lœmopsylla cheopis_; Indian Plague
Commission, _Lœmopsylla cheopis_; and McCoy and Mitzmain[203],
_Lœmopsylla cheopis_, _Ceratophyllus fasciatus_, and _Ctenopsyllus
musculi_. It has generally been considered that the _Ctenopsyllus
musculi_, above all others, would not bite man, but the last-named
observers showed that it would occasionally feed, although it would
not live long, in captivity. One of the fleas, a _Ceratophyllus
fasciatus_, was kept alive by Mitzmain for over four months on man’s
blood alone.
EXPERIMENTS PROVING THAT FLEAS CAN TRANSMIT PLAGUE.
By a series of experiments carried out in specially constructed cages
and go-downs where healthy rats in the absence of fleas were brought
in contact with plague-infected rats, the Indian Plague Commission
showed that the healthy rats would not contract the disease,
notwithstanding the fact that they were not only in intimate contact
with the sick rats, but also with the contaminated food and excreta of
the sick rats. They then showed that if fleas were introduced the
healthy rats would contract plague, the rate of progress of the
epizootic being in direct proportion to the number of fleas present.
By hanging cages containing healthy rats in cages holding infected
rats, but above the jumping distance of a flea, it was shown that the
healthy rats would remain well, while those in cages hung within 2
inches from the ground would contract plague. Thus they excluded
aerial infection. They also found that if fleas were excluded young
rats could suckle a plague-infected mother without contracting the
disease.
Guinea pigs were allowed to run in houses where cases of human and of
rat plague were known to have occurred and where many fleas were
present. These rodents served as good traps for the fleas and 29 per
cent of them contracted plague.
Most of the experiments of the Indian Plague Commission were done with
the Indian rat flea, the _Lœmopsylla cheopis_, but they also performed
27 experiments with the cat flea, _Ctenocephalus felis_, with negative
results; 35 experiments with the human flea, _Pulex irritans_, 3 of
which were successful; and 2 experiments with the _Ceratophyllus
fasciatus_, the common rat flea of Europe and North America, both of
which were successful.
In San Francisco a few experiments under purely experimental
conditions have been carried on by McCoy to determine the ability of
the squirrel flea, the _Ceratophyllus acutus_, to transmit plague.
Fleas that had been previously fed on the blood of a septicæmic
plague-infected squirrel were then allowed to feed from test tubes on
healthy guinea pigs. While the feces of some of these fleas up to four
days, when inoculated into guinea pigs, were proven to be infective,
none of those guinea pigs on which the fleas were allowed to feed
contracted plague. It might be said, however, that in no case were
they seen to eject feces while feeding, the significance of which will
be apparent later.
THE BACILLUS IN THE FLEA.
The Indian Plague Commission found that the average capacity of the
rat flea’s stomach (_Leomopsylla cheopis_) was 0.5 cubic millimeter,
and that it might receive as many as 5,000 germs while imbibing blood
from a plague rat. They further found that the bacillus would multiply
in the stomach of a flea and that the percentage of fleas with bacilli
in the stomach varied with the season of the year. In the epidemic
season the percentage was greatest for the first four days, and on one
occasion the stomach was found filled with _Bacillus pestis_ on the
twentieth day. In the nonepidemic season no plague bacilli were found
in the stomach after the seventh day. They also found that in the
epidemic season fleas might remain infective up to fifteen days, while
in the nonepidemic season but seven days, and in the latter case the
percentage of infection in animals was much less than in the epidemic
season. They showed that while one flea was occasionally able to carry
the infection this was not usual. It was found that both the males and
the females were capable of transmitting the disease.
After a number of dissections they were unable to demonstrate the
presence of bacilli anywhere but in the stomach and rectum. At no time
was anything found in the body cavity or salivary glands and but
rarely in the œsophagus, and then only when the flea was killed
immediately after feeding.
We have in San Francisco examined quite a number of serial sections of
plague-infected fleas with the same result as obtained by the Indian
Plague Commission. The bacilli are readily demonstrated, sometimes in
enormous numbers, in the gizzard, stomach, and in the rectum, but at
no time have they been found in the body cavity, the salivary glands,
or the ovary. In fact, as we are dealing with a vegetable organism and
not an animal organism, like the _Plasmodium malariæ_, we could hardly
expect to find any biologic change, except simple multiplication,
occurring in the intermediate host.
HOW THE FLEA CLEARS ITSELF OF BACILLI.
Some explanation is necessary as to why the bacilli eventually
disappear from the flea, although they seem to multiply during the
first few days. It is evident that the peristaltic action of the
stomach during the course of digestion forcing the blood at the proper
time into the rectum, finally to be ejected from the body, would in
itself cause many bacilli to be discharged, but naturally a few would
remain to multiply indefinitely. The bacteriacidal action of the blood
is soon lost after entering the flea’s stomach, but it has been shown
by proper staining that the leucocytes after the first feeding with
healthy blood contain numbers of _Bacillus pestis_, and it seems
probable that this phagocytic action is important in the cleansing
process. It has been shown that after successive feedings on the blood
of noninfected animals the power of phagocytosis is increased, and
that successive feedings on the fresh blood of animals that have been
immunized against plague still further assists and hastens the
process. When there is a frequent introduction of fresh normal or
immunized blood its bactericidal action is also instrumental in the
cleansing process.
REGIONAL DISTRIBUTION OF FLEAS ON RATS.
The location of the primary bubo in a case of plague, human or rodent,
depends upon the site of inoculation, for that group of glands will
first enlarge which has direct lymphatic connection with the area
through which the _Bacillus pestis_ enters the animal organism. The
British Indian Plague Commission found that 72 per cent of their
naturally infected rats and 61 per cent of the rats experimentally
infected by fleas had cervical buboes, while in no instance in over
5,000 plague rats was a mesenteric bubo encountered. On the other
hand, where plague was induced through feeding healthy rats with the
carcasses of plague rats a mesenteric bubo was found in 74.5 per cent
of those infected and a cervical bubo in 36 per cent. In San Francisco
in naturally infected rats a primary mesenteric bubo has never been
seen, and a cervical bubo has been seen but once. These figures show
conclusively that naturally infected rats are not infected by feeding.
It is curious, as has been pointed out by McCoy[204], that such a
large percentage of cervical buboes should be found in India, while a
cervical bubo has been seen but once in naturally infected animals in
San Francisco. Here the axillary and inguinal buboes are the rule. The
Indian Commission found that the commonest situation to find fleas on
guinea pigs was the head and neck. They combed 53 guinea pigs to
determine the regional distribution of fleas, and found that 65.3 per
cent were taken from the neck and head. This would account for the
preponderance of cervical buboes in guinea pigs observed in their
work, and inferentially for the preponderance of cervical buboes found
in naturally infected rats. Thinking that the predominating rat flea
in San Francisco, the _Ceratophyllus fasciatus_, might be the carrier
of the infection and that it might prefer a different part of the body
than the _Lœmopsylla cheopis_, McCoy and Mitzmain carried on a series
of investigations to determine the regional distribution of fleas on
the rat’s body, but this has shown that while the _Ctenopsyllus
musculi_ seems to be generally confined to the head and neck, the
_Ceratophyllus fasciatus_ and _Lœmopsylla cheopis_ are almost
invariably taken from the body, especially from the pelvic region.
ANATOMY OF THE MOUTH PARTS OF THE CERATOPHYLLUS FASCIATUS.
The following description differs somewhat from that given by
Wagner[205] and the description found in the Journal of Hygiene, both
of which, however, refer to different species of Siphonaptera.
The mouth parts may be divided into those inside and those outside of
the head.
OUTSIDE THE HEAD.
The epipharynx, or pricker, is a long, slender, hollow organ. Its
cavity is closed distally, and proximally connects with the hoemocoel.
It is made up of a dorsal and a ventral portion. Its dorsal portion
ends just within the head. Its ventral portion is grooved and is
continuous with the posterior wall of the aspiratory pharynx. Its
distal extremity is slightly expanded, forming a stylet for piercing,
while the little papillæ seen along the anterior surface in many
species are absent in this one. Laterally there is a membranous
expansion which interlocks with a similar expansion on the mandibles,
forming a tube, through which the blood is sucked.
The mandibles are two in number, articulating just within the head, so
that they are capable, of independent movement. They are serrated at
their distal extremities. Above, within the head, the anterior portion
of the mandibles ends just behind the beginning of the hypopharynx, to
which it is connected, becoming practically continuous with that
organ. The posterior portion is attached to its basal element. Each
mandible contains a groove, forming practically a closed canal, which
becomes continuous with the exit duct of the salivary pump.
The rostrum (labial palpi) forms a protection and guide to the
mandibles and epipharynx. Its first portion is unpaired and
articulates within the head, with its basal element. At the apex of
its first portion it bifurcates, forming a paired organ, which is
divided into a varying number of pseudojoints, depending on the
species of the flea. As it is a chitinous structure, these
pseudojoints, areas in which there is little chitin, enable it to
double up as the mandibles and epipharynx are inserted into the skin.
At the apex of the rostrum are some tactile hairs.
The maxillæ are triangular chitinous plates situated on either side of
that portion of the head where the biting organs emerge. These
structures serve to protect the origin of the epipharynx and
mandibles, rest upon the cutaneous surface in the act of biting,
thereby steadying the head and serving as a fulcrum when the flea
withdraws its biting apparatus when through feeding. The maxillæ have
their palpi, which are four jointed, paired organs coming out at the
anterior lower angle of the head. Their function is sensory.
INSIDE THE HEAD.
The hypopharynx is a chitinous plate forming part of the floor of the
aspiratory canal. To its under surface are attached the muscles which
operate the salivary pump. Its lower portion is connected to the
mandibles, while its upper portion is connected to the posterior
portion of the floor of the aspiratory pharynx by a membranous
ligament.
The aspiratory pharynx extends from the connection of the hypopharynx
with the mandibles to the œsophageal commissure. In a general way it
first passes upward and then turns, passing backward. Its roof is
formed by the continuation of the ventral surface of the epipharynx,
while its floor is formed by the hypopharynx below and above by the
chitinous layer which is continuous with the œsophagus. The anterior
end of this particular portion curves strongly downward, where it is
attached to the upper portion of the hypopharynx by a membranous
ligament. In a general way it may be divided into a vertical and
longitudinal portion. The longitudinal portion expands laterally, so
that its capacity is greatly increased when dilated. Into the floor of
this longitudinal portion empties the vertical part of the aspiratory
pharynx, and at the junction of the two there seems to be a valvular
arrangement, preventing blood from escaping after it has entered the
upper part of the aspiratory canal. The œsophagus starts at the
œsophageal commissure and ends in the gizzard. It is not expanded as
in some insects, forming a gullet, but is practically the same
diameter throughout its entire extent. It is lined with chitin,
surrounded by a delicate basement membrane.
The gizzard is a mushroom-shaped organ, opening into the stomach and
receiving the contents of the œsophagus and the aspiratory pharynx.
From its anterior concave inner surface project a number of
finger-like processes that arise from a basement membrane. They are
lined with chitin, and each one near its base contains an elongated
nucleus. These processes reach to the center of the gizzard and in a
general way point towards the opening into the stomach. The gizzard is
surrounded by circular bands of muscle fibers. Its function is not
entirely understood. Wagner[205] has pointed out that these processes
may act as whips to defibrinate the blood. It is more probable that
their action is mainly valvular, preventing regurgitation of blood
from the stomach.
The stomach of a flea is large and is capable of great distention. It
is composed of a layer of secretory cells, resting on a basement
membrane, the organ being surrounded by muscle fibers passing in
different directions. The epithelial surface is thrown into little
projections like villi. As absorption occurs in the stomach, these
villi, or projections of the epithelial cells, may serve to increase
the absorptive surface as well as serving a glandular function. At the
anterior end of the stomach are the cecal glands.
The intestine is short, receives the excretion from the Malpighian
tubules, and ends in the rectum. In the rectum may be seen the
so-called “rectal glands.” All of the alimentary canal, with the
exception of the stomach, is lined with chitin. The stomach and the
rectum are capable of peristaltic movement.
The salivary glands, four in number, two on each side of the anterior
part of the stomach, are simple acinous glands, lined with a single
layer of secreting cells. The lumen of the glands is large and acts as
a reservoir for the salivary secretion. The ducts from these glands
unite to form a single duct which passes beneath the subœsophagal
ganglion and empties into the salivary pump. This duct is lined on its
inner surface by a spiral arrangement of chitin, giving it a very
characteristic appearance.
DESCRIPTION OF FIGURE SHOWING MOUTH PARTS.
1. Epipharynx.
2. Mandibles.
3. Rostrum, paired portion.
4. Rostrum, unpaired portion.
5. Maxilla.
6. Maxillary palpus.
7. Salivary grooves.
8. Basal element of rostrum.
9. Basal element of mandibles.
10. Salivary pump.
11. Salivary duct.
12. Vertical portion, aspiratory canal.
13. Longitudinal portion, aspiratory canal.
14. Œsophagus.
15. Œsophageal ganglia.
16. Muscles operating aspiratory canal.
17. Hypopharynx.
18. Muscles operating salivary pump.
19. Ligament connecting hypopharynx with floor of aspiratory canal.
[Illustration:
PLATE I.
MOUTH PARTS OF CERATOPHYLLUS FASCIATUS.
]
THE ACT OF BITING.
The epipharynx, or pricker, makes an opening into the skin, through
which the mandibles are inserted. These organs, by means of their
serrations and independent movement, then enlarge the opening as with
a saw, permitting them, with the epipharynx, to pass deeper and deeper
until the points of the maxilla rest upon the cutaneous surface. The
labial palpi serve as a protective case when the organs are not in
action. When in action they serve as a guide to the piercing organs,
but are not inserted into the skin. They double up like a bow, on each
side, the bend of the bow becoming greater and greater as the biting
apparatus passes deeper and deeper. Mitzmain[206] has pointed out that
the spring-like action of this bow may assist the flea to withdraw the
mandibles and epipharynx.
During the process of penetration the salivary pump receives saliva
from the salivary glands and pumps it down, through the channel in the
mandibles, into the wound. It will be seen that the hypopharynx, being
attached above by a membranous ligament and connected intimately with
the mandibles below, moves downward with these organs as they pass
through the skin. At the same time the muscles attached to its under
surface and the salivary pump contract, enlarging the lumen of the
pump. When the mandibles are retracted the salivary pump collapses,
thereby forcing the saliva out with the movement upward of the
mandibles. At the proper time the muscles operating the aspiratory
pharynx contract, drawing the canal open and aspirating blood through
the canal made by the approximation of the epipharynx and mandibles
and into the aspiratory pharynx. When full, the muscles relax from
before backward and the pharynx, by means of the elastic reaction of
its chitinous lining, contracts and forces the blood backward through
the gizzard and into the stomach. It has already been pointed out that
the finger-like processes in the gizzard probably act as valves to
prevent regurgitation from the stomach.
HOW THE FLEA INFECTS ITS HOST.
The exact method by which the flea can transmit plague from animal to
animal has, in our opinion, never been satisfactorily explained. There
have been several explanations offered: First, that the rat may eat
the flea. Miller[207] has found that the _Hepatazoon perniciosum_ is
transmitted from rat to rat through the rat eating the mite, _Lelaps
echidninus_, which acts as the intermediate host. We know, however,
that when a rat is fed on plague material a mesenteric bubo is the
rule, while in naturally infected rats a mesenteric bubo is a rare
condition. This, then, negatives the possibility of plague being
contracted through eating the flea.
Another explanation is that the infection comes from the saliva
injected at the time of biting. We have already stated that after
repeated examinations, both by dissecting out the salivary glands and
by serial sections of the entire flea, plague bacilli have never been
demonstrated in these glands or anywhere outside of the alimentary
tract.
Another explanation has been advanced, that the bacillus is introduced
by the contaminated mandibles. It is not possible to exclude this as a
means of infection, although the Indian Plague Commission made
numerous investigations and was unable to demonstrate the bacillus on
the mandibles.
The possibility of infection taking place by regurgitation from the
stomach has also been considered. As the stomach is guarded by the
finger-like processes in the gizzard which seem to act as competent
valves, and as the movement of the blood aspirated by reason of the
mechanism already explained is in a backward direction, it would seem
improbable that there is any regurgitation from the stomach.
The most plausible explanation that has been advanced has been based
on an observation that blood-sucking insects at the time of biting
frequently eject a drop of blood from the rectum. We know that the
rectum may contain numerous plague bacilli, and it is supposed that
this blood ejected in the vicinity of the bite is either brought in
contact with the slight wound by the feet or mandibles of the flea
itself or is rubbed in as a result of scratching. Verjbitski has shown
that an emulsion of the feces of fleas or any plague material when
placed upon the bitten part before the expiration of twenty-four hours
is sufficient to give the animal plague. After twenty-four hours the
animals did not develop plague, it being supposed that the slight
wound in the skin made by the biting apparatus had healed. It is
probable that this ejection of blood is purely accidental and does not
necessarily occur at the time of biting, but it is likely that the
insect had just previously had a full meal, which had been digested
and passed into the rectum. In the many biting experiments done by
McCoy and Mitzmain they report never having seen this ejection of
rectal contents taking place. It might also be stated that where they
used plague-infected fleas none of the animals developed plague after
being bitten.
ENUMERATION OF FLEAS THAT HAVE BEEN FOUND ON RATS.
Various writers have reported the following fleas taken off rats:
Family SARCOPSYLLIDÆ Taschenberg.
Genus DERMATOPHILUS.
1. _Dermatophilus cæcata_ Enderlein.—Seventeen specimens (females)
were found by Doctor Enderlein on the skin behind the ears of a
specimen of _Mus rattus_ from Saopaulo, Brazil.
Genus ECHIDNOPHAGA Olliff.
2. _Echidnophaga gallinacea_ Westwood.—Tiraboschi has found this flea
on the _Mus rattus_ in Italy.
3. _Echidnophaga rhynchopsylla_ Tiraboschi.—This flea has been taken
in Italy from _Mus rattus_ and _Mus alexandrinus_. It has been
described by Rothschild under the name of _Echidnophaga murina_.
Family PULICIDÆ Taschenberg.
Genus CERATOPHYLLUS Curtis.
4. _Ceratophyllus fasciatus_ Bosc.—This is the common rat flea of
Europe and the United States. It has also been found in Cape Town,
Australia, and is occasionally found on rats in India.
5. _Ceratophyllus londiniensis_ Rothschild.—This flea has been taken
off mice in England; off rats in Italy (_Ceratophyllus italicus_
Tiraboschi) and has been found once on _Mus rattus_ in San Francisco,
Cal.
6. _Ceratophyllus acutus_ Baker.—This is the common flea of the
California ground squirrel; and has been taken off _Mus norvegicus_ in
San Francisco, Cal.
7. _Ceratophyllus anisus_ Rothschild.—This flea has been described by
Rothschild from Yokohama, Japan, taken off _Felis_ sp. One specimen
was found in San Francisco, Cal., taken off _Mus norvegicus_.
8. _Ceratophyllus niger_ Fox.—This flea is commonly found in San
Francisco, Cal., in chicken yards and sparrows’ nests and has also
been found on rats, _Mus norvegicus_, and on man.
9. _Ceratophyllus consimilis_ Wagner.
10. _Ceratophyllus lagomys_ Wagner.
11. _Ceratophyllus mustelæ_ Wagner.
12. _Ceratophyllus penicilliger_ Grube.
These fleas have been taken off _Mus norvegicus_ in Europe.
Genus PULEX Linn.
13. _Pulex irritans_ Linn.—This flea is widely distributed throughout
the world, and while essentially the human flea has been found on many
different species of animals and has frequently been encountered on
rats. A very large number of specimens have been taken off rats in San
Francisco, Cal.
Genus LŒMOPSYLLA Rothschild.
14. _Lœmopsylla cheopis_ Rothschild.—This is the common rat flea in
tropical and subtropical countries. It has also been found in seaports
of the temperate zone, where it has been brought by ship rats.
Ninety-eight per cent of the rat fleas in India are of this species.
It has been found in Australia, where it was described by Tidswell
under the name of _Pulex pallidus_. In the Philippine Islands, where
it was described by Hertzog as the _Pulex philippinensis_. It has been
found in Brazil, where it was described by Baker as _Pulex
brasiliensis_, and Tiraboschi has found it in Italy, where it has been
described as the _Pulex murinus_. This flea has been frequently found
on man in India.
Genus CTENOCEPHALUS Kolenati.
15. _Ctenocephalus canis_ Curtis.—This is the common dog flea found in
many parts of the world and is frequently taken off rats.
16. _Ctenocephalus felis_ Bouché.—This is the common cat flea and is
also a widely distributed species. Frequently taken off rats.
Genus CTENOPSYLLUS Kolenati.
17. _Ctenopsyllus musculi_ Dugés.—In England this flea is commonly
found on the domestic mouse. It has a wide distribution and has been
found on rats and mice in Europe, South Africa, India, Australia,
Mexico, and other places, and has been taken off _Mus norvegicus_,
_Mus rattus_, and _Mus musculus_ in San Francisco, Cal.
Genus NEOPSYLLA Wagner.
18. _Neopsylla bidentatiformis_ Wagner.—This flea has been taken off
_Mus norvegicus_ in the Crimea.
Genus HOPLOPSYLLUS Baker.
19. _Hoplopsyllus anomalus_ Baker.—This is one of the common
groundsquirrel fleas of California and has been found on _Mus
norvegicus_ in San Francisco and Palo Alto, Cal. That these squirrel
fleas are occasionally found on rats is interesting from the fact that
plague has been demonstrated both in rats and the ground squirrel in
California.
Genus HYSTRICHOPSYLLA Taschenberg.
20. _Hystrichopsylla tripectinata_ Tiraboschi.—Reported by Tiraboschi
from _Mus musculus_ in Italy.
Genus CTENOPTHALMUS Kolenati.
21. _Ctenopthalmus agyrtes_ Heller.—Taken off _Mus Norvegicus_ in
England.
_The results of the identification of 19,768 fleas in San Francisco
and Oakland, Cal._
SAN FRANCISCO, 1908.
Host: MUS NORVEGICUS.
───────────┬───────────┬───────────┬───────────┬───────────┬───────────
Month. │ C. │L. cheopis.│ P. │ Cten. │ Cten.
│fasciatus. │ │ irritans. │ musculi. │ felis,
│ │ │ │ │ Cten.
│ │ │ │ │ canis.
───────────┼─────┬─────┼─────┬─────┼─────┬─────┼─────┬─────┼─────┬─────
„ │Male.│ Fe- │Male.│ Fe- │Male.│ Fe- │Male.│ Fe- │Male.│ Fe-
│ │male.│ │male.│ │male.│ │male.│ │male.
───────────┼─────┼─────┼─────┼─────┼─────┼─────┼─────┼─────┼─────┼─────
April to │1,343│2,510│ 485│ 837│ 31│ 76│ 78│ 211│ 16│ 31
July 31 │ │ │ │ │ │ │ │ │ │
August │ 489│ 883│ 145│ 228│ 156│ 206│ 27│ 90│ 17│ 22
September │ 543│1,180│ 655│ 930│ 339│ 387│ 33│ 109│ 46│ 119
October │ 254│ 435│ 509│ 652│ 59│ 64│ 9│ 45│ 6│ 18
November │ 129│ 252│ 256│ 288│ 52│ 69│ 20│ 54│ 6│ 6
───────────┼─────┼─────┼─────┼─────┼─────┼─────┼─────┼─────┼─────┼─────
│2,758│5,260│2,050│2,935│ 637│ 802│ 167│ 509│ 91│ 196
───────────┴─────┴─────┴─────┴─────┴─────┴─────┴─────┴─────┴─────┴─────
Host: MUS RATTUS.
───────────┬─────┬─────┬─────┬─────┬─────┬─────┬─────┬─────┬─────┬─────
│ 23│ 43│ 3│ 3│ 0│ 0│ 17│ 16│ 1│ 0
│ 4│ 7│ 1│ 0│ 9│ 16│ 3│ 3│ 0│ 0
───────────┼─────┼─────┼─────┼─────┼─────┼─────┼─────┼─────┼─────┼─────
│ 27│ 50│ 4│ 3│ 9│ 16│ 20│ 19│ 1│ 0
───────────┴─────┴─────┴─────┴─────┴─────┴─────┴─────┴─────┴─────┴─────
Host: MUS MUSCULUS.
───────────┬─────┬─────┬─────┬─────┬─────┬─────┬─────┬─────┬─────┬─────
│ 4│ 10│ 1│ 0│ 0│ 0│ 2│ 10│ 0│ 0
│ 11│ 10│ 1│ 6│ 4│ 4│ 0│ 3│ 1│ 1
───────────┼─────┼─────┼─────┼─────┼─────┼─────┼─────┼─────┼─────┼─────
│ 15│ 20│ 2│ 6│ 4│ 4│ 2│ 13│ 1│ 1
───────────┴─────┴─────┴─────┴─────┴─────┴─────┴─────┴─────┴─────┴─────
OAKLAND, CAL., 1909.
Host: MUS NORVEGICUS.
───────────┬─────┬─────┬─────┬─────┬─────┬─────┬─────┬─────┬─────┬─────
February │ 135│ 304│ 166│ 178│ 1│ 1│ 229│ 506│ 1│ 3
March │ 253│ 456│ 167│ 215│ 2│ 5│ 125│ 243│ 1│ 2
April │ 227│ 479│ 105│ 129│ 0│ 1│ 62│ 143│ 0│ 1
───────────┼─────┼─────┼─────┼─────┼─────┼─────┼─────┼─────┼─────┼─────
│ 615│1,239│ 438│ 522│ 3│ 7│ 416│ 892│ 2│ 6
───────────┴─────┴─────┴─────┴─────┴─────┴─────┴─────┴─────┴─────┴─────
Host: MUS ALEXANDRINUS.
───────────┬─────┬─────┬─────┬─────┬─────┬─────┬─────┬─────┬─────┬─────
April │ 1│ 5│ 0│ 0│ 0│ 0│ 0│ 0│ 0│ 0
───────────┴─────┴─────┴─────┴─────┴─────┴─────┴─────┴─────┴─────┴─────
This does not include a few other specimens of different species taken
from _Mus rattus_ and _Mus norvegicus_, which have been included under
the heading of “Enumeration of fleas which have been found on rats.”
SYNOPSIS OF FLEAS COMMONLY FOUND ON RATS.
A. WITHOUT A COMB OF SPINES ON THE PROTHORAX OR THE HEAD.
1. Two bristles on the gena, an ocular bristle placed
below the eye, an oral bristle placed just above
root of maxilla. Mesothorax not divided by an
internal incrassation. Claspers in male forming
prominent hump, claw like and covered by hairy
flap. An irregular row of about 10 teeth on inner _Pulex
side of hind coxa irritans_.
2. Two bristles on gena, an ocular placed in front of
and just above middle of eye, an oral bristle
placed just above root of maxilla. Mesothorax
divided by internal incrassation, claspers not
forming prominent hump, not claw like, not
covered by hairy flap. A regular row of about six _Lœmopsylla
teeth on inner side of hind coxa, cheopis_.
AA. WITH A COMB OF SPINES ON PROTHORAX BUT NOT ON HEAD.
3. Three bristles on lower genal row, upper genal row
represented by three or four small bristles
running along anterior margin of antennal groove.
Eye present, about five hairs on second joint of
antenna, not as long as third joint. Maxillary
palpi not as long as labial palpi. Labial palpi
reach to apex of fore coxa. Spines on posterior
tibia in pairs of about five groups. Head of male _Ceratophyllus
flattened on top, fasciatus_.
AAA. WITH A COMB OF SPINES ON THE PROTHORAX AND ON THE HEAD.
4. Eye present, seven spines on lower margin of gena. _Ctenocephalus
Spines on posterior border of tibia in pairs canis_ or
_felis_.
5. Eye absent, four spines on hind margin of gena.
Spines on posterior tibia single and in a close _Ctenopsyllus
set row musculi_.
DESCRIPTION OF PLATE II.
────────────────────────────────────────────┬──────────────────────
Fig. 1. Clasping organs of male. │P Process.
„ │F Finger.
„ │M Manubrium.
„ │IX St Ninth Sternite.
────────────────────────────────────────────┼──────────────────────
Fig. 2. Head of female. │
────────────────────────────────────────────┼──────────────────────
Fig. 3. Terminal abdominal segments, female.│8 T Eighth Tergite.
„ │8 St Eighth Sternite.
„ │10 T Tenth Tergite.
„ │10 St Tenth Sternite.
„ │Sp Spermatheca.
„ │Sty Stylet.
────────────────────────────────────────────┼──────────────────────
Fig. 4. Hind tibia. │
CERATOPHYLLUS FASCIATUS Bosc.
[Plate II.]
_Head._—Evenly and gently rounded in the female, flattened on top in
the male. Frontal notch distinct. Eye present, placed low down in
head. Gena acutely pointed posteriorly. Maxilla triangular. Maxillary
palpi not as long as the labial palpi. Labial palpi reach to apex of
anterior coxa, 5-jointed. Antennal groove in the male reaches to top
of head, in the female to within one-third. There are 3 bristles on
the lower genal row, the middle of which is the smallest, while the
upper genal row is represented by 3 small bristles, extending along
the edge of the antennal groove. In the male the lowermost bristle is
frequently paired. There are several fine hairs above the eye. The
occiput contains the normal row of apical bristles, the lowest of
which is the largest. There is one bristle back of the middle of the
antennal groove and a number of fine hairs along the posterior margin
of the antennal groove. The antenna is 3-jointed, the first joint
contains a row of about 5 very short fine hairs, while the second
joint contains about 5 not as long as the third joint.
[Illustration:
PLATE II.
CERATOPHVLLUS FASCIATUS, BOSC.
]
_Thorax._—The pronotum has one row of about 10 bristles, and a
ctenidium composed of about 16 or 18 spines. The mesonotum has a
posterior row of about 10 long bristles and there is an anterior row
of more numerous smaller ones. The metanotum has also a posterior row
of about 10 large bristles, with an anterior row of more numerous
smaller ones, while still anterior to this there are 5 or 6 still
smaller bristles. The metathorax contains 8 or 10 bristles which are
small anteriorly, larger posteriorly. On the sternum of the metathorax
there are 2 large bristles, while the episternum has 3 smaller ones.
On the epimerum are 2 bristles placed anteriorly and 3 or 4
posteriorly, one of which is on the apical margin.
_Abdomen._—The first stigma is nearly in line with those of the other
abdominal segments. There are two rows of bristles on the abdominal
tergites, a posterior of about 12 or 14 and an anterior of smaller,
less numerous bristles. The antipygidial bristles in the female are 3
in number on each side, of which the middle is the longest, and the
inner one the smallest. The male has but 2 antipygidial bristles on
each side. The sternites from the third to the sixth have a single row
of about 10 bristles, while the seventh has about 12. The metanotum
has 2 teeth on each side, as have the first and second abdominal
tergites. The third and fourth abdominal tergites have 1 tooth on each
side.
_Legs._—The fore coxæ are normally clothed. The fore femur has on the
outer side 11 or 12 fine bristles irregularly disposed, while on the
mid femur there is a row of about 3 to 5 bristles on the inner
surface. The hind coxa has no patch of spines on the inner side, while
on the inner surface of the hind femur there is a row of about 5 to 7
bristles. The spines on the posterior tibia are in pairs of six
groups, while on the outer surface there is a row of about 7 bristles.
None of the apical bristles of the tarsi are as long as the next
succeeding joint. The fifth tarsal joints on all the legs have 5
lateral spines.
Length of joints of tarsi:
Mid tarsi (♂) 8 7 4½ 3 7
Hind tarsi 18 11 7 4 8
Mid tarsi (♀) 8 7 5 3½ 7
Hind tarsi 21 13 8 5 8
_Modified segments._—(♂). The manubrium of the claspers is straight
and narrow, while the process extends upward as a short, blunt cone,
where at the tip there are several fine hairs. The lower margin is
evenly and gently rounded. The finger is short, extending but a little
above the process. It is concave on its anterior surface and convex on
its posterior, and from the posterior margin there are 2 large and 2
small bristles alternating. Two long heavy bristles arise from the
process below the insertion of the finger. The ninth sternite is
broad, with a deep sinus in its posterior border. Its lateral surface
contains numerous fine hairs, these hairs being somewhat larger just
beneath the sinus. Along the dorsal border of the tenth sternite there
are 3 heavy bristles in line. At the tip of the tenth tergite there is
one heavy bristle. Besides these heavy bristles in this segment there
are numerous fine hairs.
(♀) The eighth tergite contains just anterior to the sensory plate
about 12 small hairs while just beneath the sensory plate there are 2
long bristles. Lower down there is a patch of about 6 bristles and on
the apical margin 4 to 6. The stylet is short, cylindrical, slightly
larger at the base than at the tip, where there is a long bristle. On
the under surface arises a fine hair. Substylar flap (tenth sternite)
has along its margin numerous hairs.
DESCRIPTION OF PLATE III.
────────────────────────────────────────────┬──────────────────────
Fig. 1. Clasping organs of male. │P Process.
„ │M Manubrium.
„ │F Finger.
„ │IX St Ninth Sternite.
────────────────────────────────────────────┼──────────────────────
Fig. 2. Head of female. │
────────────────────────────────────────────┼──────────────────────
Fig. 3. Terminal abdominal segments, female.│8 T Eighth Tergite.
„ │8 St Eighth Sternite.
„ │10 T Tenth Tergite.
„ │10 St Tenth Sternite.
„ │Sp Spermatheca.
────────────────────────────────────────────┼──────────────────────
Fig. 4. Hind coxa inner surface. │
LŒMOPSYLLA CHEOPIS Rothschild.
[Plate III.]
_Head._—Abruptly rounded. Flattened on top in ♂. Eye present. No
ctenidia on head. Antennal groove in the ♀ reaches to within one-third
of the top of the head. In ♂ reaches to top of head. Gena obtusely
pointed posteriorly. Maxilla triangular. Maxillary palpi are not as
long as labial palpi. Labial palpi reach to apex of fore coxæ,
4-jointed. Anterior edge of antennal groove overlapped by chitinous
flap. On posterior edge of antennal groove are a number of small
bristles, these being most distinct in the male. The first antennal
joint in the male contains 4 or 5 hairs at its outer edge, while
transversely there is a row of several fine hairs. The second joint
has a row of fine hairs not as long as the third joint. Divisions
marking separations of third joint most pronounced on dorsal edge. Two
bristles on gena. The oral bristle placed low down just above the base
of the maxilla; the ocular bristle in front and just above the middle
of the eye. Six bristles on the posterior margin of the occiput on
each side with 2 back of the antennal groove.
[Illustration:
PLATE III.
LŒMOPSYLLA CHEOPIS, ROTHSCHILD.
]
_Thorax._—The pronotum is without a ctenidial comb, and has one row of
about 14 bristles. The mesonotum, the broadest of the three thoracic
nota, also has a single row of about 12 bristles. The metanotum has a
single row of about the same number. The mesosternite contains about 5
bristles. The pleura of the metathorax is normally divided. The
sternum contains 2 bristles, 1 anterior and 1 posterior. The
episternum contains 1 bristle, and the epimerum contains 2 rows of
bristles, an anterior row of 7 and an apical row of the same number.
_Abdomen._—The first abdominal tergite contains 2 rows of bristles, an
anterior and a posterior of about 6 bristles each, while the next 6
contains but a single row of about 14 bristles each, the lowest placed
just below the stigma. From the seventh tergite springs a single
antipygidial bristle. The sternites contain a single row of 8 or 10
bristles.
_Legs._—The fore coxa is normally clothed. The fore femur has on its
outer surface about 8 fine bristles. The mid femur has a single row of
about 6 bristles, while the hind femur has a row of the same number.
The hind coxa has on its inner surface a regular row of about 6 teeth.
The hind tibia has on its posterior border 5 groups of spines in
pairs, while on its outer surface there are about 8 small bristles in
a row. The apical bristle on the second tarsal joint of the hind leg
reaches to about the middle of the fifth tarsal article. The fifth
tarsal article on all of the legs has 4 lateral spines and a subapical
pair of hairs.
_Modified segments._—(♂) The manubrium of the claspers is short and
narrow. There are two free processes, the upper one, the finger, being
broadest and wider at the tip than at the base, its upper border being
more convex than the lower border and containing a number of bristles.
The ninth sternite is club-shaped, is nearly straight on its dorsal
margin, and the ventral margin contains a row of fine bristles from
base to apex.
(♀) No bristles in front of the sensory plate. Along its apical margin
externally there is a row of about 12 long bristles, and internally a
row of less numerous, shorter bristles. Laterally there is a more or
less regular row of about 8 bristles, and between this row and the
apical row 3 or 4 more.
DESCRIPTION OF PLATE IV.
────────────────────────────────────────────┬──────────────────────
Fig. 1. Clasping organs, male. │10 T Tenth Tergite.
„ │10 St Tenth Sternite.
„ │P Process.
„ │F Finger.
„ │M Manubrium.
„ │IX St Ninth Sternite.
────────────────────────────────────────────┼──────────────────────
Fig. 2. Head of female. │
Fig. 3. Last tarsal joint of hind leg. │
────────────────────────────────────────────┼──────────────────────
Fig. 4. Terminal abdominal segments, female.│8 T Eighth Tergite.
„ │8 St Eighth Sternite.
„ │10 T Tenth Tergite.
„ │10 St Tenth Sternite.
„ │Sp Spermatheca.
────────────────────────────────────────────┼──────────────────────
Fig. 5. Hind tibia. │
CTENOPSYLLUS MUSCULI Dugés.
[Plate IV.]
_Head._—The frons is prominent anteriorly, giving the head somewhat
the shape of a fez. There are 4 spines on the posterior border of the
gena. The antennal groove reaches to the top of the head. The
maxillary palpi are shorter than the labial palpi, which reach to
about two-thirds of the fore coxa and are 5-jointed. Maxilla
triangular. Eyes absent. At the most prominent part of the frons
anteriorly there are two short thick spines, while below these,
running along the anterior margin, there are 5 bristles. Above there
is an oblique row of 4 bristles, with 1 more placed near the top of
the antennal groove. Between this oblique row and lower bristles there
are numerous fine hairs. On the occiput there is a subapical row of
about 7 bristles on each side, while in front of this are 3 oblique
rows of bristles, the first containing 3, the second 4, and the third
5. On the posterior margin of the antennal groove there are several
small hairs. On the first joint of the antenna there are about 3
hairs, while on the second joint there are 4 or 5, the longest
somewhat longer than the third joint.
_Thorax._—The pronotum has an anterior row of about 10 bristles, and a
ctenidium of about 24 spines. The mesonotum contains about 4 rows of
bristles, more or less regularly disposed, each row consisting of
about 8 or 9 bristles. The metanotum has 2 rows of bristles, a
posterior row of about 10 bristles, and an anterior of the same
number, while there are several smaller bristles in front of this. The
mesothorax contains about 10 bristles. The episternum of the
metathorax has 2 bristles, and on the sternum there is 1 large one.
The epimerum has 2 rows of 4 bristles each, with 1 large one at the
apical margin.
[Illustration:
PLATE IV.
CTENOPSYLLUS MUSCULI, DUGES.
]
_Abdomen._—The first abdominal tergite has 2 rows of 10 bristles each,
the posterior being comprised of the larger bristles. The next 6
tergites have 2 rows of bristles each, a posterior of large bristles,
about 12 in number, and an anterior of smaller bristles, also 12 in
number. On the apical edge of the metanotum there are 2 small teeth on
each side. The first abdominal tergite contains 3 such teeth while the
second and third have 1 each on each side. At the apex of the seventh
tergite in the female there are 4 antipygidial bristles, sometimes 5.
The male has but 3 antipygidial bristles. The abdominal sternites from
the third to the sixth have a single row of 6 bristles. The seventh
has a row of about 16 bristles.
_Legs._—The fore coxa has about 32 large bristles more or less
regularly disposed in 6 oblique rows. The hind coxa is without teeth
on the inner surface. The mid femur is without bristles on its lateral
surfaces. The hind femur is also without a row of bristles on its
lateral surfaces. The spines on the posterior border of the tibia are
single and in a close set row. The apical spines of the second tarsal
joint of the hind legs are shorter than the third joint. The last
tarsal joint on all the legs contains 4 lateral spines and a subbasal
pair situated between the first lateral pair.
_Modified segments._—(♀) Just beneath the pygidium is 1 long bristle.
On the eighth tergite there is a patch of hairs, 6 of which are on the
apical margin and about 5 or 7 anterior to these. The stylet is short,
almost as wide at the base as at the tip, where there is a long hair.
Posteriorly to this bristle there springs another one from the under
surface.
(♂) Manubrium of the claspers is narrow, curved at the tip. The finger
reaches to the level of the process, has a stout pedicle, is flat on
its anterior border, and is decidedly convex on its posterior border,
where there are 4 bristles. The shape of the ninth sternite is shown
in the figure.
DESCRIPTION OF PLATE V.
────────────────────────────────────────────┬──────────────────────
Fig. 1. Clasping organs of male │P Process.
„ │F Finger.
„ │M Manubrium.
„ │IX St Ninth Sternite.
────────────────────────────────────────────┼──────────────────────
Fig. 2. Head of female. │
────────────────────────────────────────────┼──────────────────────
Fig. 3. Terminal abdominal segments, females│8 T Eighth Tergite.
„ │8 St Eighth Sternite.
„ │10 T Tenth Tergite.
„ │10 St Tenth Sternite.
„ │Sty Stylet.
„ │Sp Spermatheca.
────────────────────────────────────────────┼──────────────────────
Fig. 4. Hind coxa, inner surface. │
PULEX IRRITANS Linnæus.
[Plate V.]
_Head._—Evenly and abruptly rounded in both sexes. Frontal notch
absent. Eye large. Maxillary palpi longer than the labial palpi.
Labial palpi reach to about half the length of the anterior coxa and
are 4-jointed. The mandibles are broad and markedly serrate. Maxillæ
triangular. Antennal groove short and wide, closed behind, thickened
on edges, and reaches to top of head in both sexes by chitinous
thickening. Second joint contains 8 or 9 fine hairs, shorter than the
third joint. Division of the third joint only to be seen on dorsal
surface. Two bristles on the gena, one placed low down just above the
maxilla, the other below the eye. From the lower margin of the gena
occasionally may be seen a small tooth. One bristle on the occiput
near the posterior lower angle. A few fine hairs on the posterior edge
of the antennal groove.
_Thorax._—The thoracic nota each contain a single row of about 10 or
12 bristles. There is no ctenidium on the pronotum. The mesosternite
is narrow and is not divided by an internal incrassation. The
episternum of the metathorax is large and contains about 2 or 3
bristles and is not quite separated from the sternum anteriorly. The
epimerum has an anterior row of about 7 or 8 bristles and an apical
row of about 6.
_Abdomen._—Each of the abdominal tergites, with the exception of the
first, has a single row of 8 or 10 bristles. The first has 2 rows of
about 4 each. The sternites from third to seventh have a single row of
about 6 bristles. There is one short antipygidial bristle on each
side.
_Legs._—The hind coxa has on its inner surface posteriorly a number of
fine hairs, while anteriorly there are 10 or 12 teeth in an irregular
line. The hind femur has on its inner surface a row of about 8 or 9
bristles. The spines on the posterior tibia are in pairs, and there
are about 7 bristles in a line on its outer lateral surface. The
apical bristle of the second tarsal joint of the hind leg reaches to
about the middle of the fifth joint. The last tarsal joints of all the
legs contain 4 lateral spines and a subapical pair, and between the
third and last lateral spine there is a hair.
_Modified segments._—(♀) The eighth tergite has no bristles above the
pygidium but has numerous short stout bristles laterally and on and
close to the apical margin. The stylet is short and stout and has at
its tip a long hair. The tenth sternite and tergite contain numerous
fine hairs, those on the sternite confined to the apical edge.
(♂) The male claspers are quite characteristic. The manubrium is large
and curved and points ventrally. The claspers have two processes, the
lower of which, with the finger, form together a kind of claw which is
covered by the other process forming a flap, quite hairy on its upper
margin. The ninth sternite is described very well by Rothschild[208]
as “boomerang” shaped. The eighth tergite has a small manubrium.
[Illustration:
PLATE V.
PULEX IRRITANS, LINNÆUS.
]
DESCRIPTION OF PLATE VI.
────────────────────────────────────────────┬──────────────────────
Fig. 1. Clasping organs of male │F Finger.
„ │M Manubrium.
„ │IX St Ninth Sternite.
────────────────────────────────────────────┼──────────────────────
Fig. 2. Head of male. │
────────────────────────────────────────────┼──────────────────────
Fig. 3. Terminal abdominal segments, female │8 T Eighth Tergite.
„ │8 St Eighth Sternite.
────────────────────────────────────────────┼──────────────────────
Fig. 4. Hind coxa and femur, inner surface. │
CTENOCEPHALUS CANIS Curtis.
[Plate VI.]
_Head._—Strongly and evenly rounded in both sexes. Eye large. Maxilla
triangular. Maxillary palpi about as long as labial palpi. Labial
palpi reach to two-thirds of anterior coxæ, 4-jointed. Seven spines
along the lower margin of the gena. The posterior angle of the gena
ends in a small tooth. Occasionally this may be absent. Antennal
groove in the female reaches to within one-third of the top of head
and is prolonged upwards by a chitinous thickening and in the male
reaches almost to top of head. Two bristles on the gena, one placed
well toward the anterior lower angle and the other in front of the
eye. Usual number of bristles on posterior margin of the head, with 2
large ones back of the antennal groove. About 8 hairs on the second
joint of the antenna nearly as long as the third joint.
_Thorax._—A row of about 10 bristles on the pronotum, with a ctenidium
of about 14 to 16 spines. Two rows of bristles on the mesonotum, a
posterior of about 12, another of more numerous smaller bristles
placed well anteriorly. The metanotum contains a single row of about
10 or 12 bristles. The episternum of the metathorax has 3 or 4 stout
bristles, while the epimerum contains an anterior row of about 10
bristles and a posterior row of about 9.
_Abdomen._—The first abdominal tergite contains 2 rows of about 4
bristles each, while the other tergites to the seventh contain a
single row of from 12 to 16 bristles. The stigmata are large. There is
a single antipygidial bristle on each side. The sternites from third
to seventh have a single row of 4 bristles each.
_Legs._—The hind coxa has on its inner side a patch of from 6 to 12
spines, while the hind femur has a row of 10 or 12 bristles on its
inner surface. The spines on the posterior border of the hind tibia,
with the exception of the apical, are in pairs, while in the apical
group are about 3 stout bristles. The apical spine of the second joint
of the hind leg reaches to nearly the middle of the fifth joint. On
the fifth joint of all the legs there are 4 lateral spines and a
subapical pair, and between the third and fourth lateral spines there
is a hair.
_Modified segments._—(♀) The eighth tergite has no hairs back of the
stigma. The apical margin is rounded at the apex and contains 8 or 10
bristles. The stylet is short and wide and contains at its tip a long
and a short bristle.
(♂) The manubrium is short and narrow. The movable finger of the
clasper is short, thick, swollen at its middle, bluntly rounded at its
extremity, and contains on its upper border numerous hairs and a few
on its lower border.
Rothschild[209] has pointed out certain differences between the
_Ctenocephalus canis_ and _Ctenocephalus felis_. The differences are
that in the female of the felis the head is longer and more pointed.
This difference is not so pronounced in the male. Also certain
differences in the shape of the claspers and the number of bristles in
the episternum and epimerum of the metathorax and the hind femur,
those in the _C. canis_ being more numerous. Also that group of
bristles on the posterior border of the hind tibia between the fifth
pair and the apical bristles consists of two in the _Ctenocephalus
canis_, while there is but a single bristle with a small hair in the
_Ctenocephalus felis_.
REFERENCES.
Endnote 201:
1909, McCoy.—“Plague Bacilli in Ectoparasites of Squirrels.” Public
Health Reports, Vol. XXIV, No. 16.
Endnote 202:
1908, Schumann.—“A Disease of Rats Caused by Mites.” Centralblatt f.
Bact., Oct. 30th.
Endnote 203:
1909, McCoy and Mitzmain.—“An Experimental Investigation of the
Biting of Man by Fleas Taken from Rats and Squirrels.” Public Health
Reports, Vol. XXIV, No. 8.
Endnote 204:
1908, McCoy.—“A Report on Laboratory Work in Relation to the
Examination of Rats for Plague at San Francisco, California.” Public
Health Reports, Vol. XXIII, No. 30.
Endnote 205:
Wagner.—Aphanipterologische Studien aus dem zootomischen
laboratorium der Universität zu St. Petersburg.
Endnote 206:
1908, Mitzmain.—“How a Hungry Flea Feeds.” Entomological News,
December.
Endnote 207:
1908, Miller.—“Hepatazoon Perniciosum (N. G. N. SP.). A
Hæmogregarine Pathogenic for White Rats; With a Description of the
Sexual Cycle in the Intermediate Host; A Mite (Lælaps Echidninus).”
Bull. No. 46, Hyg. Lab. U. S. Pub. Health and Mar. Hosp. Serv.,
Wash.
Endnote 208:
1908, Jordan and Rothschild.—“Revision of Non-Combed Eyed
Siphonaptera.” Parasitology, Vol. I, No. 1.
Endnote 209:
1901, Rothschild.—“Notes on Pulex canis, Curtis, and Pulex felis,
Bouché.” Entomologist’s Record, Vol. XIII, No. 4.
1905, Rothschild.—“Some Further Notes on Pulex canis, Curtis, and
Pulex felis, Bouché.” Novitates Zoologicae, Vol. XII.
[Illustration:
PLATE VI.
CTENOCEPHALUS CANIS, CURTIS.
]
RODENTS IN RELATION TO THE TRANSMISSION OF BUBONIC PLAGUE.
By Surgeon RUPERT BLUE,
_United States Public Health and Marine-Hospital Service_.
Man has associated the rat with bubonic plague since the dawn of
history. The monuments and coins of the earliest times yield abundant
evidence of this association. Æsculapius, the god of the healing art,
is represented by the Greeks with a rat at his feet. An early
scriptural reference may be found in the first Book of Samuel in the
fifth and sixth chapters. The historian records therein the occurrence
of a fatal epidemic of “emerods” in the land of the Philistines
coincident with an invasion of “mice.”
The inhabitants of southern China in recent times have learned to look
upon the finding of sick and dead rats in their homes as a harbinger
of evil, in fact, as a forerunner of that dread scourge—“wan-yick,” or
plague. In the villages and cities of the Kwantung and Kwangsi
provinces, as recorded by medical missionaries, epizootic plague
almost invariably precedes an outbreak among human beings. So well is
this fact known to the common people that many seek safety in flight,
feeling assured that in a short time “yang-tzu” or “wan-yick” will
claim a harvest of victims among those who remain.
Doctor Mahē, sanitary officer for the port of Constantinople, in 1889,
called attention to the fact that epidemics of plague were always
announced by a great mortality among rats and mice. In 1894 Yersin
reported the fatal epizootic among rats then prevailing in Canton and
Hongkong coincident with the outbreak of plague among the Chinese.
Recent researches have confirmed these observations and a great deal
has been added to the literature of plague, especially in relation to
its mode of transmission. Indeed, it should be said that wherever the
disease has prevailed in recent years the relation of rats to its
spread has been observed, and that since the discovery of the specific
bacillus by Yersin and Kitasato, in 1894, bacteriological
investigations have shown that there is no difference morphologically
or culturally between the bacilli of human and rat plague. Moreover,
the gross and microscopic lesions in the lymph nodes are practically
the same, and the _B. pestis_ recovered in both fulfills the
postulates of Koch.
Nothing was definitely known, however, of the mode of transmission of
the disease from rat to rat or from rat to man until the completion of
the experimental work of the Indian Plague Commission. Simond, Ogata,
Thompson, and Koch each expressed the belief that the infection was
transferred by the rat flea. Nuttall (1897) and Simond (1898)
demonstrated the presence of _B. pestis_ in the bodies of bugs
(_Cimex_) and fleas which had been taken from plague-sick rats, and
the latter observer, in the same year, succeeded in transmitting the
disease from rat to rat without contact.
The work of the Indian Plague Commission was undertaken (1905) with a
view to establishing the exact relationship between epizootics among
rats and epidemics among men, and included both field and laboratory
observations. The experiments of Gauthier and Raybaud (1903) and of
Simond were repeated on a larger scale and greatly improved in that
all rats and fleas used were first identified as to species. The
findings of the commission may be briefly summarized as follows: That
fleas and bugs taken from plague-sick rats contain _B. pestis_, and
that some of them remain alive in the bodies of the insects from five
to sixteen days; that plague is conveyed by the bites of fleas which
have previously fed on the blood of animals suffering with the
disease; that rat fleas bite man; that under experimental conditions
the infection is not transferred from rat to rat in the absence of
fleas.
A careful study of the findings of the workers in India justifies the
assumption that plague is a disease of the rodent primarily and
accidentally, and secondarily a disease of man. An analysis of the
epidemiological facts collected in San Francisco leads to the same
conclusion. As a result our practice with regard to suppressive
measures and quarantine procedure has undergone a radical change in
the last decade. If the infection is flea-borne from rat to man in the
majority of cases, then the extermination of the rat should be the
first principle upon which to base a campaign. In the former
contribution on the subject (1907) I stated that “if we destroy the
host there is no longer danger of infecting the parasite.” This basic
principle has been recognized and successfully applied in two
campaigns against plague in San Francisco. First in the outbreak in
Chinatown in 1903–4, and again in the larger epidemic of 1907.
The outbreak of 1907 began May 27, a little over a year after the
great fire and earthquake, but no cases were discovered between that
time and mid-August when the disease began to appear in various parts
of the city. The source of infection was, in all probability, a
recrudescence from a focus which was not destroyed in the campaign of
1903–4. There occurred 160 cases with 77 deaths, the last case
appearing January 30, 1908. The following table shows the incidence of
human plague:
─────────────────────┬───────┬───────
Year. │Cases. │Deaths.
─────────────────────┼───────┼───────
1907. │ │
May │ 1│ 1
August │ 13│ 6
September │ 56│ 25
October │ 34│ 25
November │ 41│ 12
December │ 13│ 7
1908. │ │
January │ 2│ 1
─────────────────────┼───────┼───────
Total │ 160│ 77
─────────────────────┴───────┴───────
EPIDEMIOLOGICAL OBSERVATIONS IN SAN FRANCISCO.
Abundant epidemiological data associating the rat[AE] with plague have
been collected in San Francisco. For the purpose of illustration a
detailed reference to a few cases will be made. Two small boys
(October, 1907) while playing in an unused cellar found the body of a
dead rat. The corpse was buried with unusual funeral honors. In
forty-eight hours both were ill with bubonic plague. A laborer finding
a sick rat on the wharf picked it up with the naked hand and threw it
into the bay. He was seized three days later with plague. Doctor C.
and family lived in a second-story flat over a grocery store in the
residence section. Being annoyed for some days by a foul odor the
doctor caused the wainscoting around the plumbing to be removed. One
or two rat cadavers were found in the hollow wall. In two or three
days the two members of the family who used the room sickened, one
dying on the fifth day of cervical bubonic plague. It is probable that
infected rat fleas were set free by the removal of the wainscoting.
Footnote AE:
_M. norvegicus_ and _M. rattus_.
Dead rats were frequently found in or near houses where plague had
occurred. Immediately upon the discovery of a case of plague trained
men were sent into the neighborhood and a thorough search made for
rats. This work consisted in the removal of defective wooden floors
and walls of insanitary buildings and other harboring places.
Extensive rat catacombs were frequently found in these operations. In
the yard of a house in which 4 cases had occurred 20 cadavers were
found under the board covering. In the walls of a Chinese restaurant
87 dead rats were uncovered.
Very little can be said of the relation of mice (_M. musculus_) to the
epidemic. While many thousands were trapped, only a few hundred were
examined microscopically and in these no infection was found. They are
nonmigratory in habit and for this reason are not considered of much
importance from an epizoological standpoint.
Transmission from man to man was observed in but a small percentage of
cases, 3 per cent to be exact. In these the probability of
transference by fleas (_P. irritans_) or by bugs (_Cimex_) must be
admitted. When more than one case occurred in a house a common source
of infection was indicated, such cases occurring simultaneously or
within from forty-eight to seventy-two hours after the first.
Deratization was the measure mainly relied upon. After an infected
house was rat proofed, and the harboring places in the block
destroyed, no further cases occurred.
The course of epizootic plague was not interrupted at any time by
climatic conditions, there being as many cases in proportion to the
rat population in the winter of 1908 as there were at the height of
the epidemic. The last case of human plague occurred January 30, 1908,
but the infection remained active among rats for eight months longer,
or until October 21, 1908. (See following table.)
─────────┬─────────┬─────────┬─────┬────────────┬────────┬─────────────
Month. │ Number │ Number │ Per │ Average │Rainfall│Character of
│examined.│infected.│cent.│temperature.│ in │ days.
│ │ │ │ │inches. │
─────────┼─────────┼─────────┼─────┼────────────┼────────┼─────────────
1907. │ │ │ │ °F. │ │{Clear, 13.
September│ 1,002│ 27│ 2.69│ 60.6│ 0.11│{Part cloudy,
│ │ │ │ │ │15.
│ │ │ │ │ │{Cloudy, 2.
─────────┼─────────┼─────────┼─────┼────────────┼────────┼─────────────
│ │ │ │ │ │{Clear, 10.
October │ 2,679│ 23│ .86│ 60.6│ 1.36│{Part cloudy,
│ │ │ │ │ │10.
│ │ │ │ │ │{Cloudy, 11.
─────────┼─────────┼─────────┼─────┼────────────┼────────┼─────────────
│ │ │ │ │ │{Clear, 14.
November │ 3,954│ 36│ .88│ 57.8│ .04│{Part cloudy,
│ │ │ │ │ │13.
│ │ │ │ │ │{Cloudy, 3.
─────────┼─────────┼─────────┼─────┼────────────┼────────┼─────────────
│ │ │ │ │ │{Clear, 6.
December │ 4,308│ 48│ 1.11│ 52.4│ 3.66│{Part cloudy,
│ │ │ │ │ │11.
│ │ │ │ │ │{Cloudy, 14.
─────────┼─────────┼─────────┼─────┼────────────┼────────┼─────────────
1908. │ │ │ │ │ │{Clear, 5.
January │ 6,622│ 70│ 1.05│ 50.8│ 4.88│{Part cloudy,
│ │ │ │ │ │11.
│ │ │ │ │ │{Cloudy, 15.
─────────┼─────────┼─────────┼─────┼────────────┼────────┼─────────────
│ │ │ │ │ │{Clear, 11.
February │ 11,700│ 45│ .38│ 51.0│ 5.39│{Part cloudy,
│ │ │ │ │ │12.
│ │ │ │ │ │{Cloudy, 6.
─────────┼─────────┼─────────┼─────┼────────────┼────────┼─────────────
│ │ │ │ │ │{Clear, 20.
March │ 19,263│ 52│ .26│ 54.8│ .90│{Part cloudy,
│ │ │ │ │ │10.
│ │ │ │ │ │{Cloudy, 1.
─────────┼─────────┼─────────┼─────┼────────────┼────────┼─────────────
│ │ │ │ │ │{Clear, 17.
April │ 15,524│ 34│ .21│ 56.3│ .22│{Part cloudy,
│ │ │ │ │ │10.
│ │ │ │ │ │{Cloudy, 3.
─────────┼─────────┼─────────┼─────┼────────────┼────────┼─────────────
│ │ │ │ │ │{Clear, 17.
May │ 11,311│ 20│ .13│ 55.4│ .76│{Part cloudy,
│ │ │ │ │ │12.
│ │ │ │ │ │{Cloudy, 2.
─────────┼─────────┼─────────┼─────┼────────────┼────────┼─────────────
│ │ │ │ │ │{Clear, 16.
June │ 13,624│ 4│ 0.02│ 55.3│ 0.01│{Part cloudy,
│ │ │ │ │ │9.
│ │ │ │ │ │{Cloudy, 5.
─────────┼─────────┼─────────┼─────┼────────────┼────────┼─────────────
│ │ │ │ │ │{Clear, 11.
July │ 11,204│ 2│ .017│ 57.4│ .02│{Part cloudy,
│ │ │ │ │ │17.
│ │ │ │ │ │{Cloudy, 3.
─────────┼─────────┼─────────┼─────┼────────────┼────────┼─────────────
│ │ │ │ │ │{Clear, 11.
August │ 10,988│ 0│ .0│ 57.3│ .01│{Part cloudy,
│ │ │ │ │ │10.
│ │ │ │ │ │{Cloudy, 10.
─────────┼─────────┼─────────┼─────┼────────────┼────────┼─────────────
│ │ │ │ │ │{Clear, 16.
September│ 15,902│ 0│ .0│ 59.3│ .29│{Part cloudy,
│ │ │ │ │ │9.
│ │ │ │ │ │{Cloudy, 5.
─────────┼─────────┼─────────┼─────┼────────────┼────────┼─────────────
│ │ │ │ │ │{Clear, 16.
October │ 10,178│ 2│ .019│ 58.8│ .061│{Part cloudy,
│ │ │ │ │ │7.
│ │ │ │ │ │{Cloudy, 8.
─────────┴─────────┴─────────┴─────┴────────────┴────────┴─────────────
The rats examined for September, 1907, were very largely collected
from the badly infected districts; the remaining months give a truer
picture of the extent of the epizootic in the entire rat population.
THEORIES AS TO THE CAUSE OF SEASONAL PREVALENCE.
The marked seasonal prevalence of plague in man in San Francisco may
be given as additional proof of the association of the rat with its
spread. In the cold, rainy season, from December to April, the
epidemic ceases while the epizootic is apparently not influenced. The
anomaly is accounted for when we remember that the rat and its
parasites are very susceptible to cold and rain. It is then that the
animal seeks a warm, comfortable place from which it does not venture
until driven thence by dire necessity. In other words, the association
of the rat with man is not so intimate in winter, while the reverse is
true of the relation of rat with rat. The rains, while interrupting
the overground migrations and domiciliary visits of rats, drive them
to overcrowded burrows and harboring places. Another factor should be
mentioned in this connection. Human fleas (_P. irritans_), and
probably rat fleas also, are markedly reduced in numbers at that
season of the year. We must conclude, therefore, that the seasonal
prevalence of plague in man is due to the effect of climatic
conditions upon the habits of rats and the life history of the insect
carriers of the bacilli.
An examination of the foregoing should convince everyone that all
former theories as to the prolonged viability of _B. pestis_ in
contaminated soil or in polluted streams, and of the periodical spread
of the infection therefrom, are no longer tenable. It may also be
stated that insanitary conditions, except in so far as they furnish
food and shelter to rats and other vermin, play no important rôle in
the continuance of plague. This general revision has also eliminated
overcrowding as an important factor. In the absence pneumonic cases,
and of suctorial insects, this _bête noire_ of the sanitarian may be
disregarded.
THE OCCURRENCE OF PLAGUE IN THE MARMOT OF ASIA AND THE GROUND SQUIRREL
OF CALIFORNIA.
Rudenko (1900) first pointed out the possibility of contagion by the
“Tarbagan,” a species of the _arctomyinæ_ found in Siberia. He
observed a connection in 1894 between this rodent and an outbreak of
plague in a Cossack family of Soktuewsk. According to Beliatsky and
Zabolotny, each having been an observer in the same field, the natives
of Siberia and Mongolia often acquire plague in this manner. Le Dantec
and other writers have called attention to the probable susceptibility
of the marmot (_Arctomys bobac_), a hibernating rodent of India and
China. The marmot of Thibet, in the opinion of this writer, is the
natural animal host and purveyor of the virus. The literature of the
subject presents no bacteriological evidence, however, of such a
relationship, and plague in the _arctomyinæ_ of Asia is merely an
hypothesis. There is positive evidence though of the susceptibility of
the tree squirrel (_Sciurinæ_) to plague infection. Dr. Alice Corthorn
(1898) reported the finding of a plague-infected squirrel in one of
the outbreaks in the Bombay Presidency.
PLAGUE INFECTION IN GROUND SQUIRRELS.[AF]
Footnote AF:
Genus Citellus, Oken; subgenus Otospermophilus. “California
Mammals,” Frank Stephens.
The demonstration of natural plague in the California ground squirrel
(_Otospermophilus beecheyi_) is perhaps the most important observation
of the antiplague work of the service in 1908. The existence of a
plague epizootic in Contra Costa County was suspected as early as the
summer of 1903, and efforts were made at that time to collect sick and
dead rodents for bacteriological examination. In August (1903) two
fatal cases of human infection occurred in widely separated sections
of the county. The investigation which followed failed to connect
either with a previous case of human plague, but showed an association
with ground squirrels. These deaths occurred during a fatal epizootic
among ground squirrels and suggested a connection which unfortunately
was not confirmed.
None of the circumstances were forgotten, however, and in the second
campaign, begun in September, 1907, in San Francisco, inspectors were
detailed to examine all persons dying in the area under suspicion. No
plague was reported that autumn and winter. Fatal cases occurred and
were reported by the inspectors in July, 1908, as follows: A boy (J.
F.) died July 15, near Concord, and a young woman (M. P.) died July
28, on a ranch 10 miles from Martinez. The two were not associated. An
investigation was ordered at once and a force of trappers was hurried
to the scene with instructions to collect squirrels from the ranches
in the vicinity. The first plague-infected squirrel was found August 5
on the ranch where the boy had died July 15. Of 425 squirrels
collected from August 1 to October 12, 4 showed the gross and
microscopic lesions of natural plague.
A lad (F. M.) sickened August 5, 1908, in Los Angeles, Cal., after
being bitten by a sick ground squirrel. A polyadenitis, which
afterwards proved to be plague, developed in a few days. A dead
squirrel was found nearby and pathological specimens taken from it
were sent to the United States Plague Laboratory in San Francisco.
McCoy recovered _B. pestis_ from the tissue of the animal. This was
the only case of plague reported in Los Angeles. In order to complete
the list of those who contracted plague in the country, two other
cases should be mentioned. F. S., a pregnant woman, died of
bubosepticæmic plague near Concord, Cal., February 29, 1904. The _B.
pestis_ was recovered in pure culture from the axillary glands. In
April, 1906, a school boy of east Oakland developed a multiple plague
adenitis. Investigation showed that he had shot and handled ground
squirrels in the country four or five days before his illness.
THE NATURAL HABITAT OF PLAGUE.
The location of the natural habitat of plague has concerned
sanitarians for many years. Not a few have settled upon India as the
endemic center, while others associate China with the epidemics which
have devastated Europe from remote times. Le Dantec, a recent writer,
suggests the “lofty mountains” between India, Thibet, and China as the
exact location, and selects the rodent (marmot) of that region as the
natural enzootic host.
A panzootic leaves in its wake enzootics of plague in various
countries which persist until the rodents upon which they thrive are
either exterminated or rendered immune. At varying intervals epidemics
spring from them and finally cease with the exhaustion or destruction
of the enzootic foci. Plague disappears in time from these temporary
abodes and retires to its original habitat in India or China.
Of serious import in this connection is the fact that all the
conditions necessary for the establishment of a permanent focus of
plague exist on the Pacific coast of the United States. The broad
valleys and lofty mountains of this region are rich in the
_arctomyinæ_, there being no less than 12 species in California alone.
In the high Sierras the marmot (_Marmota flaviventer_),[AG] a species
of the natural enzootic host of Le Dantec, is found in great numbers.
The ground squirrel infests the valleys and foothills in an unbroken
chain from Oregon to the Mexican border. Once planted in this ideal
soil, infection may never be uprooted or its growth and extension
controlled. Small outbreaks will occur here and there, and periodical
visitations of greater magnitude may be expected in cities where a
combination of epidemiological factors is permitted.
Footnote AG:
“California Mammals,” Frank Stephens.
The facts as set forth in this paper have caused grave apprehension in
the minds of those who have been at all conversant with the conditions
in the transbay counties since 1903. At that time the writer
recognized the probability of the establishment of a permanent focus
of plague in that locality, and subsequent discoveries have proven the
correctness of the assumption. This changes the aspect of the problem
from that of a local infection to one of national importance. Once
established in such a rural community, plague is dislodged with
difficulty and only after a campaign covering a considerable length of
time. Being a national problem it can be best solved by the Federal
Government.
REFERENCES.
The Croonian Lectures on Plague, W. J. Simpson; Journal of Hygiene,
Volume VI, No. 4; Volume VII, No. 6; Volume VIII, No. 2; Plague among
the Ground Squirrels of California, W. B. Wherry, Journal Infectious
Diseases, Volume V, No. 5; California Mammals, Frank Stephens.
RODENT EXTERMINATION.
By Passed Asst. Surg. WILLIAM COLBY RUCKER,
_United States Public Health and Marine-Hospital Service_.
It should be remembered that rodents are extremely wily creatures and
that any campaign against them is a contest between the wit of man on
the one hand and acute animal instinct on the other. The rat, by his
constant association with man, has become extremely wary, and is
frightened by anything in the least out of the ordinary. They will eat
the bread on which poison is spread so carefully that they will leave
behind the poison and take practically all the bread; they will open
traps by pressing down the pan, and they have been known to repeat
this operation several times within an hour, entering the trap, eating
the bait, and then liberating themselves. At other times they will
enter the trap and stand on the pan with their hind legs, eat the
cheese, then carefully turn around and back out. This, of course, is
not possible with snap traps, but they have been known to spring them
by causing pieces of wood to fall upon them, after which the bait
would be eaten. Rats are found wherever food exists in abundance or
where they can find suitable breeding and nesting places.
Rodent extermination is a problem, with difficulties arising from the
animal’s highly developed regard for self-preservation. In main, the
rat requires two conditions for life. He needs plentiful food and
places suitable for nesting and breeding. Eliminate either of these
elements and you drive away your rats. Yet the problem remains far
more difficult than shown in the simple terms of the above equation.
The fabulous speed at which rats multiply will baffle all but the most
determined and efficient efforts to exterminate them. Under normal
conditions each female bears 3 litters a year and each litter produces
10 young. Under conditions ideally favorable, it has been computed
that 1 pair of rats will in five years, providing all can live so
long, increase to 940,369,969,152. Such a result is, of course,
impossible in nature, for it means that every rat born of the original
pair survive five years; that every litter of 10 contains 5 males and
5 females; and that the ideally favorable conditions persist. On the
other hand, rodent existence is an unending struggle in which an
enormous percentage succumbs; the ratio of half males and half females
does not hold; and ordinary conditions of life are hardly even
favorable. Nevertheless, the above proves emphatically that no rat
eradication can be effective unless the breeding is curtailed. Any
campaign against rodents must aim (_a_) to slaughter the greatest
possible number of those already living and (_b_) to prevent the
possibility of further breeding.
The existing rats are best attacked by trapping, by poisoning, and by
their natural enemies. Traps and poisons alone have been found
insufficient to keep pace with the rat’s speed of multiplication. The
surest of the rat’s enemies are his natural ones, and once they have
been loosed upon him his chance of escape is reduced. The cat, dog,
skunk, and other rodent foes, given a fair chance, quickly drive out
rats. But these animals do not eradicate the pest. The rats will
probably migrate to some other shelter, returning when their natural
enemies have quieted down. Absolute extermination is reached only when
conditions make the continuation of species impossible for the rat.
The size and frequency of rodent litters decreases proportionately
with every cutting off of food supplies. Separate the rat from his
pabulum and he will not breed so freely nor so often as when he is
well fed. Destroy rat habitations and make it impossible for them to
find new nesting places, and breeding will virtually cease, since the
unsheltered progeny can no longer survive, and since the starving
parent rats are driven to cannibalism in the struggle for existence.
Campaigns against rodents must cover five directions: (1) Trapping,
(2) poisoning, (3) exposing them to natural enemies, (4) cutting off
food supply, and (5) destroying existing nests at the same time that
the making of new ones is prevented.
Parenthetically, it may be noted that while these principles apply
equally to the extermination of rats in cities and in country
districts, their application must vary according to the place.
TRAPPING.
The kind of traps to be used varies with the rodent to be captured and
the locality which it infests.
CAGE TRAPS.
The large 19-inch French cage trap gives good results where rats are
plentiful. It should be made of stiff, heavy wire and well reenforced,
as a large, strong rat will force his head between the wires in a weak
trap and thus escape. Before setting, the lever on the trap should be
tested to see that it works properly. The trap should be placed on a
hard surface, with the rear end a little higher than the entrance, so
that the trap will close promptly. When setting the trap in the open
it should be fastened to a board on which about an inch of soft dirt
has been spread. Place the trap where the rat usually goes for food or
in a runway and disturb the surroundings as little as possible. It is
sometimes well to place the trap near where there is dripping water,
as the rats come there to drink. If the trap is set in hay or straw or
wood it should be covered (with the exception of the entrance) with
this material. When this is not possible it should be covered with a
piece of sacking or placed in a dark corner or beneath the floors.
When setting the traps in the sewer a dry place should be chosen.
The rat is more or less of an epicure, therefore the bait should be
changed at frequent intervals. Also he should be given food which he
is not in the habit of getting. For example: In a meat market
vegetables are the best bait, while in a location where vegetables are
plentiful fresh liver and fish heads, or a little grain, are best. The
following may be suggested as good bait to be used: Fish, fish heads,
raw meat, cheese, smoked fish, fresh liver, cooked corn beef, fried
bacon, pine nuts, apples, carrots, and corn. When trapping in chicken
yards a small chick or duckling is remarkably good. When a large
number of rats are caught in one trap, search for the female and leave
her alive in the trap, as she may call in the young or the males. The
bait should be fastened to the inner side of the top of the trap with
a piece of fine wire so that the first rat in can not force the bait
underneath the pan and thus prevent the entrance of other rats. A few
grains of barley should be scattered near the entrance of the trap and
a small piece of cheese or meat fastened to the pan with a piece of
wire. It is often well to touch the pan with a feather which has been
dipped in oil of anise or oil of rhodium. Before leaving the trap it
should be smoked with a piece of burning newspaper to kill the smell
of the human hands or the rats which have been in it. Do not handle
the trap after burning it out. When trapping in a neighborhood where
rats are known to exist the traps should not be moved for three or
four days unless they have rats in them, as it is well for the rats to
become accustomed to seeing them and thus careless about entering. It
is not wise to kill rats where they are caught, as the squealing may
frighten the other rats away.
SNAP TRAPS.
Snap or spring traps are best for use in houses and stores, with the
exception of fish and meat markets. Snap traps are best for use in
runways, beams, and shelves. It is sometimes well to disguise the trap
by covering its floor with a little sawdust or dirt. They should be
first tested to see that they work properly and that the staples are
secure. New traps should be smoked or stained to render them an
inconspicuous color.
The bait should consist of some firm material, such as fried bacon or
tough meat, and should be tied on so that the rat will be obliged to
pull on it and thus spring the trap. The trap should be placed in a
corner or close to the wall on a flat, hard surface, so that the rat
can not spring it with his tail or by walking on it.
BARREL TRAPS.
In warehouses and granaries large numbers of rats may frequently be
trapped by using a barrel or garbage can having a metal top which is
carefully balanced. Large pieces of strong cheese are placed in the
middle of the cover and a plank laid from the floor to the edge of the
barrel. The rat runs up the plank onto the smooth metallic lid which
tips and the rat is precipitated into the barrel.
In cities trapping is one of the most effective of the three methods
to slaughter rodents. The rat highways are easily discovered and in
them traps capture great numbers of the unwary. In the country one can
not so readily determine the rat highway. This difficulty diminishes
the effectiveness of trapping. To make up for what is thus lost
shooting has been resorted to with good results. In Honolulu, where a
vigorous campaign against rodents is being waged, a very large
proportion of the captured rats (_Mus rattus_ and _M. alexandrinus_)
have been shot from trees. In Contra Costa County, Cal., where ground
squirrels are being exterminated, it has been found that rodents
possess an instinctive suspicion of traps and that during the summer
months shooting is not only the most practical but also about the only
effective means of attacking them. Shotguns are the weapons to use. A
rifle requires the hunter to be a better shot than is ordinarily
obtainable for such work, and, furthermore, the danger from its longer
range and from ricocheting bullets menaces cattle and farm hands who
may be working in the vicinity. As to the shot and the powder charge
for shells hunters differ. It is a different problem for every
shotgun, depending upon the gun’s caliber and choke. The principle is
to put the greatest number of the largest shot the gun will carry into
the rodent body. Thus in 10 and 12 gauge guns shoot No. 8 shot and in
16-gauge guns shoot No. 9 shot, but this varies with each individual
gun. The use of soft lead or chilled shot seems a matter for personal
preference. The charge must be as much as the gun will carry. In the
country smokeless powder becomes a necessity during summer months
since black powder is liable to ignite the dry grass and stubble.
POISONING.
PLASTER FLOUR.
Plaster flour is prepared by mixing one part dry plaster of Paris with
two parts flour or meal. When this is taken in sufficient quantity by
the rodent it produces death by the formation of enteroliths, death
occurring in from four to eight days. This is a poison of uncertain
value and is recommended chiefly on account of its cheapness and small
danger to children and domestic animals. It can not be used in wet
weather, and judging from the small number of rats found dead with
plaster casts in the alimentary canal it is not believed to be very
efficacious.
PHOSPHORUS PASTE.
Phosphorus paste is prepared by mixing crude phosphorus in the
proportion of one-half to 10 per cent in a suitable base. The latter
may consist of cheese, sugar, and oil of anise mixed together and
heated to the consistency of sirup, the phosphorus being added after
the fire has been withdrawn and the mixture begun to cool. Other bases
are cheese, corn meal, and oil of rhodium; cheese, ground fish, or
meat and oil of valerian, glucose, and a small quantity of flour.
Glucose makes an exceptionally good base, as when properly mixed the
poison thus prepared is noninflammable even when heated. The liability
to spontaneous combustion of phosphorus mixtures eliminates their use
in hay, grain, or other warehouses or places where there is danger of
fire or the invalidation of insurance. It should not be forgotten that
phosphorus deteriorates very rapidly, especially when it is exposed to
the sun.
ARSENIC PASTE.
This consists of arsenious acid combined with a base of cheese, meal,
or macerated fish. It may be placed on raisins or prunes and is to be
recommended on account of its stability, the ease with which it is
handled, and the absence of danger from fire. It should, however, be
distributed with great care, every precaution being used to place it
where it is inaccessible to children and domestic animals.
BARIUM CARBONATE.
This has not proven an effective poison owing to the fact that it is
easily decomposed by the vegetable acids, especially lactic and oleic
acid found in cheese and oil. The poisonous effect is not greatly
altered by this change. A disagreeable metallic taste is produced and
the rats will not take it.
STRYCHNINE.
Strychnine is prepared as a poison by soaking wheat over night in
water and subsequently pouring off the excess fluid and placing the
wheat in a caldron containing hot glucose and strychnia sulphate, the
latter in the proportion of one-tenth of 1 per cent. After carefully
stirring so that each grain is thoroughly coated it is dried in
shallow iron pans over a slow fire with constant agitation of the
grain, or by exposure on sheets or canvas to the rays of the sun. This
mixture may be made much more efficient by the addition of cyanide of
potassium in the proportion one-half of 1 per cent. Poisoned grain has
not been found efficient in the destruction of rats, as its bitter
taste causes them to eat little or none of it. It is, however,
particularly efficient in poisoning squirrels, as it is taken readily
by them. The chief objections to its use are its cost, difficulties of
preparation, and liability to its being taken by chickens.
CARBON BISULPHIDE.
Carbon bisulphide is not a poison so much as an asphyxiant. As the
name indicates, it is a two-to-one mixture of sulphur and carbon. The
resulting liquid preparation should be kept in air-tight cans, since
it evaporates quickly. The principle of its efficacy against rodents
is that the fumes are heavier than air and, sinking into a rat or
squirrel hole, drive out the necessary oxygen. To use bisulphide
saturate a small pad of some absorbent cotton, jute, wool, or flannel
material with the liquid, thrust this into the rodents’ burrow, and
carefully stop all apertures through which the fumes might escape.
Animal life of every sort in that burrow is quickly asphyxiated. In
buildings the use of carbon bisulphide is greatly hampered by the
difficulty to confine the gas by stopping all cracks and other
openings. Also the odors of decomposition in animals so killed stand
against its use anywhere but in the country.
Against rats and squirrels in country places carbon bisulphide has
proved one of the best of all weapons. Where it kills, it kills whole
families at a time, not one by one, as must ever be the case with
other poisons and with traps or shotguns. Not only does it kill the
rodent but it also destroys the rodent’s fleas and vermin, which is
most important. A dead infected rat is still a menace, since its fleas
may inoculate other rats and human beings with the infection. Destroy
the fleas and that greatest danger is removed. The recent campaigns
against rodents in the United States have been waged because rats and
squirrels were infected with bubonic plague; hence the added value of
carbon bisulphide. Unfortunately, though this asphyxiant proved so
effective in the work against squirrels in Contra Costa County, Cal.,
it proved to be well-nigh useless during the summer season when dry
heat checks the adobe and makes the ground generally porous.
Nevertheless, the value of carbon bisulphide, especially for sanitary
purposes, can not be easily overestimated for work in the country
during the fall, winter, and spring seasons.
Fumigants in general are effective. They possess no marked or peculiar
advantages as special weapons against rodents. Their use is limited
chiefly to warehouses, elevators, and ship holds. They are deadly to
rats in the same way that they are fatal to every sort of life. Many
difficulties and some dangers stand in the way of their use. It is
safe to advise that no one unacquainted with their action should ever
employ fumigants.
NATURAL ENEMIES.
The war upon rats carried on in San Francisco has proved the great
value of cats and dogs as natural enemies of the rat. That city now
has a law requiring all structures of 800 or less square feet and
outside certain limits to be raised high enough above the ground to
allow access to cats and dogs. (All other buildings in the city must
be rat proof.) An index to the worth of rodent foes in their
extermination points from what happened during the great London
plague. At that time the disease was supposed to be air carried; any
furry material might hold and spread infection. The magistrates
decreed that all cats and dogs should be killed to prevent plague from
lodging and traveling in their hair. Rats were thus free to live and
breed unmolested, and live and breed they did until the plague killed
them off; then and then only did the disease cease its ravages among
human beings.
DOGS.
Slight training will make excellent ratters of Fox, Irish, or Scotch
terriers. Fox terriers have proved especially valuable as retrievers
when shooting squirrels, which in one case out of five will escape to
their burrows unless sharply retrieved.
CATS.
Cats are little less valuable than dogs against rats, while they are
useless against squirrels. The ordinary cat is too well fed to attack
large rats and goes, almost solely, after mice.
All other animals naturally preying upon rodents class with wild
life—weazels, ferrets, badgers, skunks, and minks. These can be used
only in country places, where, however, their raiding of chicken coops
tends to counterbalance their value as ratters. The skunk alone is an
infrequent slayer of fowl, whereas he harvests innumerable farm pests
from worms to crickets. Yet an insurmountable prejudice against skunks
stands in the way of realizing his full usefulness against rodents. In
addition, various hawks and most owls kill off rats. Since rats come
out chiefly in the nighttime, owls have the better chance to be
serviceable in their destruction. The efficiency of these birds in
rural districts quite equals that of a dog against rats, while besides
dogs we have not as yet found a safe natural foe of ground squirrels.
But all such attacks upon rats fail of absolute eradication. One must
make it impossible for them to find sustenance and must destroy not
only all existing rat houses, but also all chance of their digging or
finding new ones.
CUTTING OFF THE RAT’S FOOD SUPPLY.
This is important not alone for its effect in a campaign upon rodents,
but equally because it necessitates sanitary care and cleanliness in
handling foodstuffs intended for humans and garbage coming therefrom.
Abattoirs and places where cattle and hogs are fattened perhaps
furnish the greatest number of rats. Stables, food-supply stores,
groceries, meat, fish and vegetable markets, restaurants, bakeries,
and the various places where food is prepared for human consumption
are usually infested. In each of the places the barriers vary
according to the nature of the premises. Rat-proof receptacles for the
foodstuffs must be installed wherever practical. In San Francisco an
ordinance requires every stable to have metal lined feed bins. Markets
and places where eatables are constantly being shifted about must be
properly screened against rats. Screening should be of heavy wire and
sufficient fineness, not larger than halfinch mesh. In all places the
food has to be raised such a height above floorings as to be beyond
the rat’s reach. This applies also to corn and grain cribs in the
country. Yet, no matter how carefully the bulk of the food may be kept
from rats, negligence in handling it, in spilling or scattering small
amounts upon floors or the ground, will nullify every precaution.
No less painstaking must be the disposition of garbage. Ordinance now
requires that all premises in San Francisco be provided with “sanitary
garbage cans.” Preferably these should be of zinc or galvanized iron
and fitted with tight covers. Under no circumstances should the cover
be allowed to remain off its can. Garbage is to be placed in a can
without delay and care must prevent the dropping of it upon the
ground. Rats once served communities as scavengers; wherever the
scavenger work is laxly done, rats are welcomed. Finally, garbage must
never be allowed to accumulate and should be removed daily, not less
often than every other day.
Special conditions, closely related to the next topic, are encountered
in large warehouses and grain sheds. Places where large quantities of
food may be stored for a length of time should be constructed of
reenforced concrete to be rat proof. Then, again, where vessels are
changing cargoes, rat-proof compounds should be erected for the
temporary storage of freights. The water fronts of seaports are
invariably rat ridden; and in San Francisco a compound for freight
held in transit was found invaluable. No effort can be spared in
keeping rats from their food if their extermination is to be
accomplished.
With regard to ground squirrels, the use of poisoned wheat very
properly enters here. With the changing season ground squirrels change
their habitat and food. During early spring these rodents come down
from their winter dwellings in the hills and seek burrows in meadow
lands and cultivated spots. Months have passed since the squirrel
tasted wheat; his fickle appetite betrays him. From the first spring
months until harvest time one can kill thousands of ground squirrels
by tempting them with poisoned wheat. But so soon as harvest time
comes, they seek new growing green stuffs to eat and thereafter, on
through winter, poisoned wheat is ineffective.
BUILDING THE RAT OUT OF EXISTENCE.
Most certain of all methods to get rid of rodents is to allow them no
place in which to live. San Francisco effects this result through its
ordinance, which requires small houses outside certain city limits to
be raised so high from the ground that dogs and cats can drive out
rats from under them, and which requires all other buildings in the
city to be rat proofed with cement or concrete. The latter
contemplates foundation walls of concrete or brick sunk at least 1
foot to 18 inches to 2 feet above that surface; the whole ground area
inclosed by their foundation walls must be covered with concrete at
least 1½ inches in thickness. Thus the entrance of burrowing rodents
is prevented. Even where buildings stand upon rock or hardpan, these
requirements should be enforced. Rock may crack, gradual weather decay
may cause crevices to be found in it unseen crannies may be found by
rodents, and once the rat lodges in rock his nest is virtually
unassailable. With hardpan it is even worse, for the rats can burrow
in it, with some difficulty, truly, but when nests are impossible
elsewhere, necessity will drive rats to find shelter in hardpan, which
will protect them quite as well as rock. In the main, these two points
of building rats out of existence, though modified, will apply to any
structure.
Yet any negligence will overthrow these safeguards. The principle is
to allow no opening within which rodents may nest. Plank sidewalks and
back yards will continue the rat nuisance even though buildings are
amply protected. Carelessness in throwing old boxes into basements or
piling old lumber or refuse within reach will supply shelter for rats
despite concreted ground area. The precaution must be constant and
consistent.
Another important phase is to cut off the rodent migrations. Prevent
rats from moving from place to place. Their time-honored highway is
through sewers. Modern sewers afford no protection, inviting rodents
to live in them as formerly. Scarcely less important, access should be
stopped. Catch-basin feeding sewers should be constructed so that rats
can not slip through into the mains, or having once gotten in, they
can not escape, and hence must drown. Farms are frequently protected
against rodent migrations by tin or zinc sheeting sunk into the ground
about a foot and a half and standing about the same height above the
surface along the fence line.
Finally, as the progress of rodents from place to place within
communities must be hindered, so must they be stopped from entering
new communities. Railroads and seagoing vessels carry great numbers of
rats in freight. The rat-proof compounds above described serve well
enough so far as railroads are concerned. With vessels it is a
different matter, and one demanding special attention, since the
rodent is only too likely to import infection from foreign harbors.
All hawsers thrown out to make boats fast should be provided with
traps to catch any rat seeking to land along the hawser. San
Francisco, about to possess a rat-proof water front, is now building
concrete wharves to prevent the landing of rodents. Every port should
be safeguarded by stone, concrete, or iron wharves and piers. As a
further protection, all ships should have permanent devices, as is now
proposed for naval construction. Levy’s system of metal conduits built
into vessels promises much in the present world-wide war upon rodents.
Rodents must be “built out of existence,” and to eradicate rats for
all time we must erect wide systems of municipal fortifications.
NATURAL ENEMIES OF THE RAT.
By DAVID E. LANTZ,
_Assistant Biologist, United States Department of Agriculture_.
INTRODUCTION.
Undoubtedly the great increase of rodent pests throughout North
America is in large part due to a general scarcity of the animals that
habitually prey upon them. Since the early settlement of the country
persistent warfare has been made on birds and mammals of prey on the
plea that they are enemies of poultry, game, and insectivorous birds.
Efforts to destroy the predaceous birds and mammals have been greatly
stimulated by the payment of municipal, county, and state bounties,
and the destruction has gone on until in many sections these animals
have nearly disappeared.
The effect of killing off the natural enemies of rodents has been to
disturb natural conditions. Rodents multiply so rapidly that they
derive an undue advantage in the struggle for existence when their
natural enemies are destroyed. The result is noticeable in the
increased depredations of rats, field mice, rabbits, and other pests.
The destruction of carnivorous wild mammals and birds by the farmer,
hunter, or game preserver is often due to misapprehension. Because one
kind of hawk preys on the farmer’s poultry is not sufficient reason
for exterminating all hawks. Nor does the fact that occasionally an
owl or a skunk destroys a chicken or a game bird justify warfare on
all owls and skunks. It is the occasional individual and not the
species that offends.
ANIMALS THAT DESTROY RATS.
The usefulness of the natural enemies of the rat must not be
overlooked in plans for its repression. Among the more important are
the larger hawks and owls, skunks, foxes, coyotes, weasels, minks, and
a few other wild mammals; as well as cats, dogs, and ferrets among
domestic animals, and snakes and alligators among reptiles.
HAWKS.
Most of the larger hawks destroy rats. Feeding only in the daytime,
they seldom find their quarry near houses and barns, where rats do not
venture out until after sunset. Besides, owing to persecution by
farmers, hawks generally keep away from farm buildings. In the open
fields, however, where rats feed in early morning and late afternoon,
hawks find many of the rodents.
The species of hawks that more commonly feed on rats are the buzzard
hawks, including the red-tailed (_Buteo borealis_ and sub-species),
the red-shouldered (_B. lineatus_), the broad-winged (_B.
platypterus_), and the Swainson (_B. swainsoni_); the rough-legged
hawks (_Archibuteo_), two species; and, to a less extent, the marsh
harrier (_Circus hudsonius_), and a few other species.
The writer has several times found the remains of rats about the nest
of the red-tailed hawk. Of the 562 stomachs of this species examined
by Dr. A. K. Fisher, of the Biological Survey, less than 10 per cent
contained poultry or game, while more than 70 per cent contained
injurious rodents.[AH] Most of the other species of buzzard hawks made
a better showing even than this, especially the Swainson hawk, which
had fed entirely on harmful rodents and insects. The stomachs of
rough-legged hawks examined nearly all contained harmful rodents and
none of them contained remains of birds of any sort.
Footnote AH:
Hawks and Owls of the United States, p. 62, 1893.
A few months ago, while walking on the Potomac flats near Washington,
the writer met some boys who had just shot a red-tailed hawk. Its crop
was greatly distended, and later examination showed that the bird had
recently eaten an enormous brown rat. Although the shooting was
contrary to law, when it was reported to the nearest policeman, his
comment was, “Oh, a hawk! Why, it’s a good thing to shoot a hawk.” The
incident illustrates the general popular prejudice against all hawks.
OWLS.
Because they hunt by twilight and at night, owls are more efficient
than hawks in destroying rats. All American owls, except the more
diminutive species, prey on the common rat. Even the little screech
owl (_Otus asio_) feeds on young rats.
Of all our species, the barn owl (_Aluco pratincola_) is preeminent as
a destroyer of rats. It lives commonly about farm buildings, sometimes
even making its nest and rearing its young in the pigeon loft without
molesting the pigeons. In such surroundings its opportunities for
securing rats are excellent, and no other wild bird is so useful on
the farm. The late Henry Newman once stated that every barn owl is
worth £5 a year to the British nation, and the value of the bird to
the American farmer is not less.
Owls, hawks, and other birds of prey that swallow their quarry whole
or in large pieces do not digest the bones, fur, and feathers. They
eject these indigestible parts in the form of large pellets, in which
the fur or feathers surround the bones. The contents of these casts
are an excellent index of the food of owls. Dr. A. K. Fisher, of the
Biological Survey, has examined 987 pellets of a pair of barn owls
that live in a tower of the Smithsonian building in Washington, and in
them found the skulls of no fewer than 192 rats (_Mus norvegicus_),
together with those of 554 common mice and 1,508 field mice (_Microtus
pennsylvanicus_).
Dr. John I. Northrop found a nest of the barn owl on Andros Island,
Bahamas. It contained two young owls and the remains of a black rat
(_Mus rattus_). The ground about the nest was covered with pellets
which contained remains of the black rat and no other species.[AI]
Footnote AI:
The Auk, vol. 8, p. 75, 1891.
The great horned owl (_Bubo virginianus_) is the largest of our
resident owls. It feeds mainly on rodents, though occasionally it
takes a fowl found roosting in an exposed situation, as on a fence or
in a tree. While it occasionally destroys game birds, the rats it
captures would probably destroy ten times as much game as the owl.
Charles Dury, of Ohio, in 1886 published a letter from O. E. Niles in
which it was stated that he counted 113 dead rats at one time under a
nest of this bird.[AJ]
Footnote AJ:
Jour. Cincinnati Soc. Nat. Hist., vol. 8, p. 63, 1886.
The snowy owl (_Nyctea nyctea_) is a rather rare winter visitor in the
northern United States. It usually arrives when the ground is covered
with snow and ordinary food is scarce. Near barns, outbuildings, and
stacks it finds its chief subsistence in the common rat; and, if
undisturbed, will stay for several weeks in the same locality,
destroying many of the pests. Unfortunately, mounted specimens of this
beautiful owl are so much in demand that the majority of them fall a
prey to the specimen hunter and the taxidermist. The destruction of
this bird should be prohibited under heavy penalties.
The barred owl (_Strix varia_), the long-eared owl (_Asio
wilsonianus_), and the short-eared owl (_Asio flammeus_) all destroy
some rats; but as they do not generally nest or live in the vicinity
of farm buildings, the rodents they capture are taken chiefly from the
fields. Occasionally a short-eared or a long-eared owl makes its
winter home in a group of evergreens near the farm buildings, and does
excellent service in clearing the premises of rats and mice.
Evergreens are desirable about a country place, if for no other reason
than that they attract owls.
The practice of indiscriminately destroying hawks and owls should be
discouraged. Game preservers especially should realize that the birds
of prey they kill would, if allowed to live, destroy rats, which in
the course of a year do many times as much harm to game as the
supposed offenders do. Besides, the birds would destroy also large
numbers of mice and injurious insects.
The farmer and the poultry grower may easily learn to recognize the
few harmful species of hawks, and should confine their warfare to
these. The practice of setting pole traps for hawks and owls is
exceedingly reprehensible, as it results chiefly in the destruction of
our beneficial owls when they come about the premises at night in
search of rats. Furthermore, the beneficial hawks and owls should have
legal protection. The larger hawks, nearly all of which are
beneficial, are slow of wing and much more likely to be shot than the
swifter and more harmful falcons.
NATIVE WILD MAMMALS.
Not many species of wild carnivorous mammals live where the common rat
is abundant. Coyotes, foxes, and a few others occasionally find a rat
in the fields, but for the most part they depend for food on native
wild rodents and other animals. Chief among the mammals that do good
work in destroying rats are skunks, minks, and weasels.
SKUNKS.
Skunks are excellent ratters, and when they take up their abode on the
premises of the farmer, they speedily destroy or drive away all rats
and mice. This statement applies equally to the large skunks
(_Mephitis_) and the little spotted skunks (_Spilogale_).
Unfortunately, skunks are seldom allowed to tenant the premises
without being molested by either dogs or men. When undisturbed, they
are inoffensive, and will stay about the farm buildings or stacks
until rats and mice are no longer to be had for food.
Skunks usually hunt by night, and hence poultry properly housed is
safe from them. The larger skunks do not climb, and can capture only
fowls that roost on the ground. Indeed, so few skunks ever learn to
kill poultry that there is no good reason for warfare on the skunk
family. Besides destroying mice and rats, the animals are invaluable
as consumers of noxious insects, especially cutworms, army worms,
white grubs, May beetles, grasshoppers, crickets, and sphinx moths.
WEASELS.
Weasels are good ratters and mousers. Several of our species come
about buildings, and often perform excellent service in destroying
rats and mice. They are more likely than the skunk to attack poultry,
for they can enter the poultry house through smaller openings. At
times weasels seem to kill for the mere love of killing, and while
occasionally this trait makes them formidable in the poultry house, it
also renders them more efficient as destroyers of rodents. A small
weasel can follow a rat into all its retreats, and will soon clear a
stackyard or shed of all rodents.
Our largest weasel, the black-footed ferret (_Putorius nigripes_),
occasionally deserts its wild haunts on the plains and comes about
buildings in search of rats and mice. In 1905, while the writer was at
Hays, Kans., one of these ferrets took up its quarters under a board
sidewalk in the business part of the village. The squealing of the
rats it killed was often heard.
As regards the destruction of poultry by weasels, the same care
necessary to exclude the rat from a poultry house will keep out the
weasel also. When so excluded, a weasel will do no harm about the
premises, but may be depended upon to drive out or kill all the rats
and mice.
MINKS.
Minks are excellent ratters, but as enemies of poultry are worse than
weasels. They destroy fish also. The great demand for mink fur causes
close trapping of these animals, and in the future they are not likely
to influence greatly the numbers of rodent pests.
DOMESTIC ANIMALS.
Among the enemies of rodents often employed as aids to rat destruction
are the dog, cat, and ferret.
DOGS.
The value of dogs as ratters can not be appreciated by those who have
had no experience with trained animals. The ordinary cur and the
larger breeds of dogs seldom make useful ratters. Small Irish, Scotch,
and fox terriers, when well trained, are superior to most other breeds
as ratters, and under favorable circumstances may be depended on to
keep premises free from rodents. Much, too, may be done by the farmer
or householder to increase the effectiveness of his dogs by removing
obstructions to their work. Corncribs and outbuildings, when of wood,
should not have floors close to the ground, but should have ample room
below to permit dogs to move about freely.
With a little preliminary training, most terriers learn to hunt rats
independently, and they thus become doubly useful on farms and in
warehouses.
CATS.
When the black rat was the dominant species in Europe and America,
cats were the chief dependence of the householder against rats; but
comparatively few cats will venture to capture a full-grown brown rat.
Then, too, the ordinary house cat is too well fed and consequently too
lazy to be an efficient ratter.
Occasionally, however, one meets with rat-killing cats whose work in
destroying the brown rat has decided value. These cats are rarely of
the fine breeds, but generally of the common “tabby” variety, kept in
barns or warehouses, fed on milk, and left to forage for their own
meat. Managed in this way, cats are far less objectionable on sanitary
grounds than when kept in the house as pets. In the country, on the
other hand, barn cats are far more likely than the house-kept ones to
run at large and prey upon birds and young poultry. Aside from the rat
itself, we have no more serious enemy of birds and game than half-wild
cats, many of which have been abandoned in fields and woods by the
thoughtless. All things considered, cats do not rank high as
destroyers of the common brown rat.
FERRETS.
Tame ferrets, like weasels, are inveterate foes of rats, and can
follow them into their retreats. Under favorable circumstances ferrets
are useful aids to the rat catcher, but their value is often greatly
overestimated. They require experienced handling and the additional
services of a well-trained dog or two to do effective work. Dogs and
ferrets must be thoroughly accustomed to each other. A noisy or
excitable dog is useless in ferreting. The ferret should be used only
to drive out the rats, which are then killed by the dogs. If an
unmuzzled ferret is sent into rat retreats under floors, it is apt to
lie up after killing a rat and sucking its blood. Sometimes the ferret
will remain for hours in a rat burrow or escape by unguarded exits and
be lost.
Such experiences often discourage the amateur ferreter. Besides,
ferrets are subject to diseases and require the greatest of care as to
their food. For these reasons the use of ferrets to destroy rats,
except in the hands of the experienced, is generally expensive and
disappointing.
OTHER ANIMALS.
MONGOOSE.
The various species of mongoose (_Herpestes_ and _Mongos_) are
destroyers of rats, and their importation into this country has often
been urged. Many years ago they were introduced into Jamaica and
Hawaii to save the sugar plantations from ravages by rats. The
mongoose has, however, proved very destructive to native birds and
poultry in the islands, and its introduction is now generally
regretted. Its importation into the United States is prohibited by
law.
ALLIGATORS.
In the South the alligator is said to destroy many rats along levees
and banks of streams, and its protection has been urged on this
account.
SNAKES.
Our larger snakes are beneficial in destroying rats, mice, prairie
squirrels, and pocket gophers. As most of the food of snakes is
obtained remote from human abodes, only a small percentage consists of
rats.
BOUNTIES ON PREDATORY ANIMALS.
Whatever may be said in favor of bounties on the larger beasts of
prey, those on hawks, owls, and the smaller fur-bearing animals can
not be justified. Payments of this sort should cease, and laws should
be enacted to protect species which careful investigations have shown
to be mainly beneficial.
A few States still pay bounties for the destruction of foxes, weasels,
skunks, minks, and raccoons. All of these, except the southern
weasels, have valuable fur, and hence should be protected as a source
of wealth. In addition they do far more good by destroying rats, mice,
and other field pests than harm to game and poultry.
The payment of bounties on hawks of any kind is open to the objection
that officials hardly ever discriminate between the harmful and the
useful kinds, even when the statutes do so. Since the beneficial kinds
are the more easily captured, public money is often paid out to reward
what really injures the community. The bounty on owls is still more
reprehensible, since owls are a more decided check to rodent increase.
The natural enemies of the rat exercise a steady, cumulative effect in
restricting the numbers of the pest. That the effect is not greater is
largely our own fault, since instead of protecting the birds and
mammals that prey on the rat, we destroy them, sometimes even offering
bounties on their heads. In future our aim should be to increase their
numbers and to protect them in every way possible.
RAT PROOFING AS AN ANTIPLAGUE MEASURE.
By RICHARD H. CREEL,
_Passed Assistant Surgeon, United States Public Health and
Marine-Hospital Service_.
To appreciate the great importance and absolute necessity of rat
proofing as an antiplague measure, it is only necessary to consider
the results that have followed its use as compared with other measures
that have been relied on in recent years in combating this disease.
These were, briefly, disinfection, evacuation, or destruction of
buildings in infected areas, preventive inoculations, and destruction
of rats either by poison or by trapping.
Plague was formerly believed to be communicable by aerial transmission
and through the agency of fomites. Sanitarians have, therefore, put
great faith in disinfection procedures, but the results have never
been satisfactory, and it is only necessary to consider the method of
transmission of plague to perceive the fatuity of bactericidal
measures. Measures intended for the destruction of fleas are also of
relatively small value. It is well worth while to destroy all fleas
possible, but if those infesting the rat population escape, the
efforts will have had little effect in preventing the spread of
plague. It is only those fleas that infest rats and their habitats
that are of importance in relation to the transmission of disease, and
it is only by rat proofing that their destruction in rat burrows and
runs can be accomplished.
Rat-proofing of individual buildings is of no recent date, but new
emphasis was laid on rat-proofing as a separate and distinct
antiplague measure by Passed Assistant Surgeon Mark J. White in an
article written in the fall of 1907.[AK]
Footnote AK:
Journal American Medical Association October 19, 1907.
Disinfecting procedures must be regarded as of minor importance in
plague prevention, except in pneumonic cases where its use is
imperative. It is not intended to depreciate the value of
disinfection, but rather to estimate its exact value as an antipest
measure. Time and money should not be wasted nor a feeling of false
security engendered by using an ineffective measure when others, as
rat proofing, of much greater value are at hand. As an example of this
might be cited an outbreak of plague in one of the refugee camps
during the recent epidemic of the disease in San Francisco. This camp
covered several blocks and housed between two and three thousand
people. The camp grounds throughout and the houses were disinfected
and disinfected well. At the same time, every effort was made to
poison and trap rats. Notwithstanding these precautions, cases
continued to occur, but when the houses were elevated there followed
an immediate cessation of plague cases in the camp.
Another case of infected premises proved equally refractory to
disinfection. The place was a large two-story frame dwelling located
in the center of the city and in a good neighborhood. The yard was
planked, as was also a part of the basement, the latter being used as
a storeroom. On November 1 there occurred in this dwelling a fatal
case of human plague, and plague rats were found at the same time. The
place was disinfected in the usual manner and thorough measures were
taken to trap and poison rats with apparent subsidence of infection,
but on January 22 a plague rat was trapped, followed by another on
January 31, after which the occupant of the building vacated it in
great alarm. All planking was then removed from the yard and basement
and concrete substituted by the owner, the place thereby being
rendered thoroughly rat proof, and no plague rats were subsequently
taken from that dwelling or in its immediate neighborhood.
In 1902 the plague outbreak was almost wholly confined to the Chinese
colony. Chinatown was made the battle ground, and among other measures
rat proofing was enforced, with the result that after the fire it was
by far the most sanitary district in the city of San Francisco from a
structural point of view. The buildings when erected were made rat
proof from cellar to garret. The Chinese had had their lesson, and to
their credit it must be stated that they responded with a greater show
of intelligence than did some of the residents in surrounding
districts.
Adjacent to the Chinese colony is the Latin quarter. In the rebuilding
of this section, no attention was paid to rat proofing; consequently
many of the buildings consisted of small shacks set on the ground or
abutting some insanitary stable, and were therefore ideal rat harbors.
On account of these conditions the natural results followed.
Chinatown, on the other hand, which had contributed in the previous
epidemic almost the entire number of plague cases during the epidemic
of 1907, did not furnish more than two or three of the plague cases
reported; that is, less than 2 per cent of the total cases reported,
while the Italian colony, including North Beach district, probably
furnished over 50 per cent of the total.
The evacuation or burning of buildings can hardly be called a
successful measure any more than a retreat can be styled a victory;
moreover, there can be no question from an economic standpoint as to
the value of rat proofing over abandonment except in a few isolated
cases of dilapidated insanitary property.
Schemes and plans for demurization, total or partial, have been as
numerous and varied as they have been unsuccessful. Traps and poisons
have been the agencies of destruction, but until some highly
communicable epizootic peculiar to rodents shall have been discovered,
absolute eradication of the rat can be considered as nothing less than
impossible.
A recognized authority on plague, Major Morehead, of the Indian
Medical Service, states that “rat destruction is of doubtful value,”
referring, of course, to trapping and poisoning when those measures
are used solely without auxiliary measures. He agrees with Japanese
authorities in their arguments that as rat populations decrease, the
breeding rate among survivors increases, due, obviously, in part at
least, to increased food supply and harboring facilities. Such a
result is assured where rat proofing is not accomplished at the same
time. This latter procedure, by destroying rat harborages and cutting
off food supplies bring about conditions unfavorable to breeding.
The total eradication of rats in a locality is not absolutely
necessary, however, to the eradication of plague. If the rat
population is kept within fairly low limits, rat centers destroyed,
and such rat population as does exist well scattered and not
congested, it is ventured that rat plague will disappear from a
locality. Plague among rats in San Francisco ceased to appear when the
number of rodents was reduced some 50 per cent, but such reduction was
accomplished only after six months of ceaseless endeavor, which
included also the rat proofing of the bakeries, stables, and markets
in the city.
It is a logical supposition that close contact is just as essential
for the propagation of plague among rats as it is for the spread of
certain communicable diseases among human beings, the increase of
cases being in direct proportion to the density of population and
closeness of contact.
RAT PROOFING OF PRIMARY IMPORTANCE.
Without the general enforcement of rat proofing antiplague measures
are bound to be more or less temporary and decidedly unsatisfactory.
This subject is of immense importance to the public, both from a
sanitary and a commercial standpoint, but the latter aspect of the
question is more apt to prove of interest to most communities.
The measures necessary to render buildings rat proof are the same,
however, whether they be instituted for sanitary or for commercial
reasons. Rat proofing will, therefore, be considered entirely from a
sanitary standpoint; but it can be understood that granaries,
bakeries, butcher shops, packing houses, dwellings, and other places,
if rat proofed for sanitary reasons, are just as much protected from
depredation of the rat as though the work had been performed for
commercial reasons alone.
Rat proofing has a twofold objective. It serves as a protection to the
inmates of a building, and excludes rodents from sources of food
supplies and harboring places. While rat proofing should be enforced
as a general measure in all plague-infected localities, it is
imperatively demanded in premises whereon have occurred cases of human
or rodent plague.
Plague-infected localities or places that contain food must be
rendered impervious to rats in order to insure the success of other
preventive measures. Rats can be trapped or poisoned only when other
food supply is excluded. A rat will enter a trap for food or will eat
poisoned preparations not because of their greater attractiveness, but
because of their greater availability. It therefore follows that rat
proofing of food supplies is a prerequisite to success in rat
eradication. The food depots requiring attention in the order of
importance are stables, meat markets, bakeries, restaurants,
groceries, warehouses, and private dwellings.
It is logical to suppose that the most common mode of infection is by
reason of plague rats dying in the walls, roofs, or floorings of human
habitations. As soon as the rat’s body is cold the fleas abandon it
for another rat, some domestic animal, or human being. The risk to
human inmates in such infected houses, therefore, is evident.
That rat proofing is a valuable measure is shown by the reports of the
British Plague Commission where are mentioned the results following
the use of rat-proof “go-downs” and those not so constructed.
Additional evidence is presented by the fact that appalling epidemics
of plague have ravaged India and the China coast, whereas in the
Philippine Islands but few people die of the disease. It would appear
that the comparatively few cases in the Philippine Islands were due to
the fact that most Philippine dwellings are rat proof by reason of
being elevated from the ground and the fact that the walls are thin
and offer no refuge whatever to rats.
RAT PROOFING IS EXPENSIVE.
The almost insuperable obstacle that will usually confront the
sanitary authorities in such work will be either the financial
inability of the unfortunate community or the sordid unwillingness to
make any expenditure that does not promise personal gain.
When the influence of the mosquito in the transmission of yellow fever
was proven, recourse was had to mosquito proofing of both the sick and
the well as a preventive measure. Rat proofing in plague is just as
rational and necessary, but the financial expenditure contemplated
thereby has been of such proportion as to cause the majority of
sanitary authorities in different parts of the world to dismiss the
idea as impossible.
To properly rat proof a city undeniably requires enormous
expenditures, but no antiplague campaign was ever waged without an
immense outlay of both money and labor. If allowed to progress
unchecked, however, plague, either through ravages of the population
or through commercial interference, is ruinous. To fight plague,
therefore, is the only alternative, and a costly campaign should be
anticipated and prepared for in advance. To merely put out traps and
poisons without the preliminary rat proofing required can be
productive of little good and no permanency. Such a plan of campaign
may be attractive because of its relative cheapness, but any city or
country that relies wholly on such measures is practicing false
economy and deferring the day of reckoning.
It becomes evident, therefore, that rat proofing is of the greatest
value as an antiplague measure, and that practical results to be
expected are much greater than with any other method.
As has already been stated, the individual premises on which plague
either among rodents or human beings has occurred demand first and
immediate attention. The work should be extended as rapidly as
possible from the point of infection so as to include the entire block
and neighboring blocks.
While the chief energies should be centered on plague-infected foci,
similar work should be carried on simultaneously throughout the city.
METHODS OF RAT PROOFING.
If plague occurs in the grounds of dwellings the following course
should be pursued: All planked-over areas, including sidewalks, that
might possibly shelter a rat should be removed, leaving either bare
ground or, at the option of the owner, gravel or concrete used, the
gravel being preferable. Small sheds should be elevated, or their
ground floors concreted. Wood sheds should probably be left without
flooring, wood kindling or other contents being piled on elevated
platforms provided for the purpose. Stables on the premises should be
treated as indicated in a subsequent paragraph relating to these
structures.
The garbage depository must be given most careful attention. It should
be a metal receptacle, preferably a galvanized can, water-tight to
prevent seepage which would attract rats, and there should be a
closely fitting lid. A can 2 feet in height without cover will not be
proof against the incursion of rats.
The rat proofing of chicken yards is a difficult task as most chickens
in private families are fed on table scraps, thereby attracting and
supporting a fair quota of rats. The entire inclosure should be
protected by wire fencing 6 feet high and of a mesh not larger than a
half inch. Ordinary poultry netting is inadequate, the mesh being too
large. The edge of the yard should be of concrete construction, the
concrete extending 1 foot upward and 2 feet inward. If, on any
subsequent inspection, rats have been found to have burrowed into the
inclosure, the entire area should be concreted, sand or earth being
allowed as a top dressing.
It would seem sufficient to confine these specifications to a feeding
pen, but in practice this will not suffice, as a mere pretext of such
a place would be built, and the housewife would continue to throw
scraps into the unprotected yard.
The dwelling house itself should receive the most careful attention.
If it is a small frame structure the cheapest and most effective means
of rendering it free from rats is by elevating it, the minimum height
being 1½ feet, measured from the most dependent joist. At the same
time, all underpinning should be freed of rubbish or other material.
It is not sufficient to raise the structure a few inches so as to
permit the entrance of cats and other enemies of the rat. Such height
and exposure must be secured as to deprive all rodents of cover.
If the house is of more substantial structure, and always if it has a
cellar or basement, concrete or some other rat-proof material should
be adopted. If sound foundation walls of stone or brick exist, then
only the addition of a concrete floor is necessary. The stopping up of
rat holes in any substance pervious to rats is at best a poor
expedient.
The grounds must be rendered rat proof by piling all loose materials
at such an elevation as will preclude rat harborage. All rubbish
should be burned or otherwise destroyed. All basement windows should
be properly protected against the ingress of rats, and if the _Mus
rattus_ be present, even second and third story windows should not be
considered too high to afford them entrance.
All loose materials on the premises should be properly piled, even
though they are in a rat-proof cellar. It is not probable that the
_Mus decumanus_ would remain or breed in any place where it could not
burrow; but no encouragement should be offered to any rodent let in by
carelessly left open doors. There have been cases where the black rat
has lived, increased, and overrun a house which was structurally rat
proof, but in which there was allowed easy access through open windows
and doors, and great piles of loose materials and dunnage furnish
harborage.
Stables are of twofold importance because they provide a source of
food supply for rats and furnish harborage. All grain must be kept in
a metal lined box or granary. A small stable is sufficiently rat proof
if it has an elevation of 2 feet with clear underpinning, provided the
floor is rendered impervious to falling grain. Barns of larger extent
are best made rat proof by concrete flooring tight on the ground, and
the area walls should be of concrete 1 foot high or of galvanized iron
of standard thickness. The ingredients of concrete should be specified
as to quality and quantity.
The windows of stables should be screened, especially if black rats be
present. To render a large livery stable rat proof, however, is hardly
practicable, owing to doors being open almost continuously, but rat
proofing even in such buildings will destroy rat harborage and limit
rat invasions to an occasional migratory rodent. With concrete
flooring and protected feed pens it should be an easy task to keep
such a building free from rats.
Finally, manure pens should be rat proof or the manure thrown into the
corner of the rat-proof stable, provided there is frequent cartage.
RAT-PROOFING ORDINANCES SHOULD BE SPECIFIC.
Any law or ordinance providing for rat proofing should specifically
state the minimum thickness of concrete and cement. Concrete 4 inches
deep with one-half inch dressing of cement or 1-inch asphalt answers
very well. Area walls if of concrete should be 6 inches thick, and the
floors should have sufficient slant to allow drainage.
Any expedient as galvanized iron sunk into the ground and made flush
with the flooring will not prove of practical value, as it allows
rat-harboring space to exist beneath the flooring, and sooner or later
rats will gain access thereto by burrowing under the iron gratings or
through the wooden flooring.
Meat markets should have concrete floors with cement or asphalt
dressing, the floors to be close on the ground and surrounded by
properly constructed foundation walls of stone or brick in cement.
Water-tight metal cans should be provided for all scraps, and
especially for the sawdust with its admixture of fine pieces of meat.
Bakeries and restaurant kitchens should be treated in the same way as
meat markets. Packing houses, slaughter pens, warehouses, and food
depots in general should be concreted.
The water front demands the greatest attention. The piers and wharves
should be of concrete or steel construction. The shipping should be
shored off from the dock, and all lines properly rat guarded. When not
in use, gang planks should be lifted. Notwithstanding these
precautions, rats will be imported from time to time, and the only
practical way to prevent their getting ashore will be the systematic
and routine fumigation of ships by the quarantine authorities.
The rat proofing of sewers is open to argument. Of all places in a
city the sewer is certainly the one where rats can die with the least
danger to the human population. For this reason the sewer should be
the last structure in a municipality to be made rat proof. The
movements and migrations of rats should be controlled to the extent of
making corner catch basins their sole means of entrance and exit to
sewers. The small and large iron-pipe mains require no attention in
this respect, but where mains are constructed of brick, and especially
where they are old and in bad repair, they should be repaired, all rat
runs leading from the sewer walls being stopped up and all blind
sewers being closed. By this means there will be prevented the
breeding of rats in these areas.
The rat proofing of catch basins by any method that would not also
block the entrance to the basin seems hardly possible. Properly
trapped basins, however, will be found almost as effective and just as
desirable.
To attain efficient rat proofing requires necessary laws or ordinances
and public sentiment favoring their enforcement. Dead-letter laws that
form no small part of many city statutes attest the fact that
favorable public opinion is almost indispensable to their enforcement.
However, well-drafted laws, clear and specific in requirement and
impartially and consistently enforced, inevitably lessen and destroy
opposition.
In the foregoing are contained general principles necessary to rat
proofing in the case of an outbreak of plague. Due allowance will have
to be made, however, for local conditions, and special considerations
as they arise, as no unvarying plan will be practical of application
in every instance.
CHOICE OF ARCHITECTURE AND BUILDING MATERIALS.
Cities and countries have from time to time wholly revolutionized
their type of buildings and constructive materials for either
commercial or æsthetic reasons. It is suggested that ports having
trade relations with countries where plague prevails should bear in
mind the advisability of taking advantage of this fact and revise
their building laws with the view to rendering all new buildings rat
proof.
Concrete has been advocated for purposes of rat proofing because of
its durability and relative cheapness. Concrete flooring or side walls
can be made more durable, however, by embedding therein steel netting
of 1 or 2 inch mesh. By this method the cost of construction will
probably be reduced, as a thinner layer of concrete would be
sufficient, and the metal would be protected, thereby adding
stability. Such construction at the same time would be doubly rat
proof.
THE INEFFICIENCY OF BACTERIAL VIRUSES IN THE EXTERMINATION OF RATS.
By M. J. ROSENAU,
_Surgeon, U. S. Public Health and Marine-Hospital Service, Washington,
D. C., now Professor of Preventive Medicine, Harvard University
Medical School_.
INTRODUCTION.
Rats are notoriously resistant to bacterial infections. About the only
exception is the plague bacillus. Plague among rats occurs both in
endemic and epidemic form. When we recall that this virulent disease,
which spreads readily from rat to rat, neither eradicates these
rodents nor, as a rule, makes any appreciable inroads on the number of
rats, we can hardly expect that an artificially induced bacterial
disease would be successful. No other known bacterial infection has
such a virulence for rats as the plague bacillus has maintained.
Epizootics of bacterial nature, therefore, can not be classed among
the natural enemies of the rat. Despite this fact persistent efforts
have been made to create artificial epizootics to combat these
dangerous and destructive rodents, but with little success.
The bacterial viruses that have been used for the destruction of rats
and mice belong to the colon-typhoid group[AL] and excite enteritis of
different characters and a septicemia.
Footnote AL:
More particularly the hog-cholera group, which includes the
para-typhoid organisms.
In 1889 Loeffler discovered and described a bacillus which he called
the bacillus of mouse typhoid (_B. typhi murium_). He isolated this
organism from a spontaneous epidemic which occurred among white mice
in the Hygienic Institute at Griefswald.[AM] He determined that this
bacillus not only caused the death of his mice in the laboratory, but
also that the infection was taken into the system of the mouse by
ingestion. He found the cultures to be especially virulent for field
mice (_Arvicola arvalis_). Loeffler gives a complete description of
the bacillus which, from a biologic standpoint, is the parent stock of
almost all subsequent work along this line. The bacillus used by
Danysz and other workers is either identical with or very closely
allied to Loeffler’s bacillus of mouse typhoid.
Footnote AM:
Loeffler, F.: Ueber Epidemieen unter den im hygienischen Institute
zu Griefswald gehalten Mäusen und über die Bekämpfung der
Feldmausplage. Centblt. f. Bakt., Orig., vol. 11, 1892, pp. 129–141.
In 1892 Loeffler[AN] personally undertook a campaign against the field
mice in Thessaly and reported satisfactory results. The depredations
carried on by the mice were checked within eight to nine days.
Footnote AN:
Loeffler, F.: Die Feldmausplage in Thessalien und ihre erfolgreiche
Bekämpfung mittels des _Bacillus typhi murium_. Centblt. f. Bakt.,
Orig., vol. 12, 1892, p. 1.
The English commission[AO] threw doubt upon the Thessaly operations
and concluded that the bacillus as a means of destruction of mice has
no value. They found the method to be expensive, affecting only one
species of mice; further, that the epidemic-like spread of the disease
in the fields was not sufficiently investigated, and that the infected
material retains its virulence only for eight days and does not permit
of being used in continued bad weather.
Footnote AO:
Wien. landw. Zeit. 1894, p. 783.
Loeffler’s optimistic report, however, stimulated many similar trials
with varying success. Practically all these efforts were directed
against mice, until 1900, when Danysz took up the subject from the
standpoint of the rat and plague.
Danysz found that Loeffler’s _Bacillus typhi murium_ proved to be
pathogenic for ordinary mice (_Mus musculus_) and for field or harvest
mice (_Mus arvicolis_), but not for rats.
The culture isolated by Laser[AP] in 1892 was pathogenic for field
mice (_Mus agrarius_); this organism killed 70 of the 76 mice which
were used as experiment animals at the Hygienic Institute at
Königsberg.
Footnote AP:
Laser, Hugo: Ein neuer für Versuchsthiere pathogener Bacillus aus
der Gruppe der Frettschen-Schweinseuche. Centblt. f. Bakt., Orig.,
vol. 11, 1892, p. 184.
Mereshkowsky[AQ] in June, 1893, isolated an organism belonging to this
group from a ground squirrel known as the Zisel (_Spermophilus
musicus_). This culture killed domestic and field mice when placed in
their food, but was not pathogenic for rats.
Footnote AQ:
Mereshkowsky, S. S.: Ein aus Zieselmäusen ausgeschiedener und zur
Vertilgung von Feld-resp. Hausmäusen geeigneter Bacillus. Centblt.
f. Bakt., Orig., vol. 17, 1895, p. 742.
The Japanese investigator Issatchenko,[AR] in 1898, briefly described
a bacillus obtained by him from gray [white?] rats, which proved
virulent for rats and mice.
Footnote AR:
Issatchenko, B.: Untersuchungen mit dem für Ratten pathogenen
Bacillus. Centblt. f. Bakt., Orig., vol. 31, 1902, p. 26.
Each of these various bacilli is of such variable virulence that it
could not be used for the destruction of all species of these rodents.
Danysz[AS] therefore conceived the notion that it would be of great
interest first to extend the field of action of one of these organisms
by increasing its virulence so that it would attack other species of
rodents, and then maintain this increased virulence at its highest
point.
Footnote AS:
Danysz, J.: Un microbe pathogène pour les rats (_Mus decumanus_ et
_Mus rattus_) et son application à la destruction de ces animaux.
Ann. Inst. Pasteur, vol. 14, 1900, p. 193.
In 1900 Danysz isolated a bacillus from a spontaneous epidemic among
harvest mice. This organism was a cocco-bacillus presenting the
general characteristics of the colon-typhoid group and resembling the
bacillus of Loeffler—_B. typhi murium_. From the first this bacillus
showed a slight pathogenicity for gray rats (_M. decumanus_). Out of
10 animals fed with a culture of this microbe 2 or 3 would die;
several others would sicken and recover; others appeared completely
refractory. The fact that a certain number of the rats fed with these
cultures always succumbed led to the hope that it would be possible to
increase the virulence of this particular microbe by the generally
accepted methods—that is to say, by a certain number of passages from
rat to rat.
Danysz first tried to increase the virulence of the organism by this
means, but he found that successive passages from rat to rat, whether
by feeding or by subcutaneous injection, ended by enfeebling rather
than increasing the virulence of the microbe. He found that it was
rarely possible to go beyond 10 to 12 passages. Sometimes the series
was stopped at the fifth passage, or even sooner, by the survival of
all the animals undergoing experiment. The result was exactly the same
if, instead of alternating each passage through the animal by a
culture in bouillon or agar, the bodies of animals dead of a preceding
passage were fed to others.
It was therefore plain that in the evolution of an epidemic caused by
this microbe it was necessary to take account of the indisputable
diminution of the virulence of the microbe, as well as the natural
resistance of the survivors.
Passage of cultures in collodion sacs inclosed in the peritoneal
cavities of rats was tried, both in interrupted series and by
alternating each sac culture with a culture in bouillon or on agar,
but the end was invariably a notable diminution of virulence when
administered by the digestive tract.
Finally, after long and painstaking procedures, Danysz obtained a very
virulent culture that, contained in flasks and kept from the influence
of light and air, preserved its virulence for several months. Planted
on agar it preserved its virulence without appreciable diminution for
two months under laboratory conditions. In bouillon, in flasks, or in
tubes stoppered with cotton it altered very rapidly.
DESCRIPTION OF THE ORGANISM.
A culture of Danysz’s virus obtained from the Pasteur Institute had
the following characteristics:
The organism is a cocco-bacillus showing distinct motility. Stains
well by the ordinary stains, but does not stain by Gram’s method.
It grows well at ordinary room temperature, also in the incubator, and
on all the ordinary media. In bouillon it produces a uniform
cloudiness in twenty-four hours. A slight scum forms after several
days’ growth, which falls to the bottom when shaken. In Dunham’s
solution it grows well, but produces no indol in twenty-four hours’
growth.
It does not coagulate milk.
It grows the whole length of the stab in gelatin, forming small
whitish colonies in the deeper portions of the tube. It does not grow
over the entire surface of the gelatin tube; does not liquefy gelatin.
It grows under anærobic conditions.
It ferments glucose bouillon, but not lactose bouillon. In glucose
bouillon it produces 1-CO_{2}, 5-H. It also produces H_{2}S.
From a general biological standpoint it is plain that this bacillus
belongs to the para-typhoid group, and is very similar to the bacillus
of hog cholera as well as the _Bacillus icteroides_, also _B.
enteritidis_, so far as its morphological and cultural characteristics
are concerned.
In the following table the fermentations produced by various members
of this group upon certain carbohydrates are shown:
─────────────┬────────┬───────────┬────────┬────────┬────────┬─────────
Organism. │Lactose.│Saccharose.│Maltose.│Mannete.│Glucose.│Levulose.
─────────────┼────────┼───────────┼────────┼────────┼────────┼─────────
B. typhosus │ − │ − │ − │ − │ − │ −
B. dysenteriæ│ − │ − │ − │ − │ − │ [AT]
Shiga │ │ │ │ │ │
B. dysenteriæ│ − │ − │ − │ − │ − │ [AT]
Kruse │ │ │ │ │ │
B. │ │ │ │ │ │
para-typhosus│ − │ − │ + │ + │ + │ +
A │ │ │ │ │ │
B. │ │ │ │ │ │
para-typhosus│ − │ − │ + │ + │ + │ +
B │ │ │ │ │ │
B. para colon│ − │ − │ + │ + │ + │ +
B. acidi │ + │ − │ + │ + │ + │ +
lactici │ │ │ │ │ │
B. hog │ − │ − │ + │ + │ + │ +
cholera │ │ │ │ │ │
B. typhi │ − │ − │ + │ + │ + │ +
murium Danysz│ │ │ │ │ │
B. icteroides│ − │ − │ + │ + │ + │ +
B. │ − │ − │ + │ + │ + │ +
enteritidis │ │ │ │ │ │
B. coli │ + │ + │ + │ + │ + │ +
communis │ │ │ │ │ │
─────────────┴────────┴───────────┴────────┴────────┴────────┴─────────
Footnote AT:
Or bubble.
EXPERIMENTS UPON RAT VIRUS IN THE HYGIENIC LABORATORY.
In 1901 I made an investigation of this pathogenic microbe (_B. typhi
murium_) applied to the destruction of rats under laboratory
conditions.[AU] One hundred and fifteen rats were fed with the
cultures in various ways during the course of these experiments with
the virus. Of these, 46 died—less than half.
Footnote AU:
Rosenau, M. J.: An investigation of a pathogenic microbe (_B. typhi
murium_ Danysz) applied to the destruction of rats. Bull. No. 5 of
the Hygienic Laboratory, U. S. Mar. Hosp. Serv., Washington, 1901,
11 p.
Most of the rats used were the gray rat (_M. decumanus_ or
_norvegicus_) and the tame white rat. A few (8) of the wild black or
house rats (_M. rattus_) were used.
The virus is in reality pathogenic for these three kinds of rats when
ingested. No special difference was noted in its effects upon the
various species.
As the work progressed it soon became evident to me that the result
depended largely upon the amount of the culture ingested. By starving
rats for a day or two and then giving them all they could be induced
to eat and drink of the cultures, a very positive result was obtained.
In one instance of 27 rats so fed all died within a week. If the rats
are given a small amount the effect is uncertain—only a few die. In
one instance I fed 70 rats with 4 agar tubes and only 7 died. Feeding
them a second time with very large quantities 9 more died. The
survivors were then fed with all they could be induced to eat every
day for a week without effect.
It seems plain, therefore, that a large primary dose proves fatal, and
a small dose is not only uncertain, but produces an immunity. This is
a very important factor, for it is likely that in the wild state rats
would often partake of an amount too small to cause death. Such rats
may then subsequently eat large amounts of the culture with impunity.
It would seem then that, after all, the virus is not so different from
the laying of a chemical poison, depending as it does for its effect
upon the amount ingested. A chemical poison, however, does not possess
the disadvantage of producing an immunity. Another disadvantage
possessed by the virus is the rapid deterioration in virulence which
occurs when it is exposed to the action of air and light, or when it
becomes dry, as is very apt to happen when laid out for rats in the
wild state.
Since these early experiments, tests have been made of various rat
viruses in the Hygienic Laboratory, and the results are given in the
following pages:
AZOA.
Series 1. Single feeding of azoa in oatmeal. Rats starved twenty-four
hours before feeding. Three out of eight animals died in four, five,
and seven days, respectively. Micro-organisms resembling the
predominant one of azoa could not be isolated from their hearts’
blood. The organs of these dead rats were fed to fresh rats with the
result that one of the three died. It must be mentioned that the
mortality among our fresh rats was nearly as high as that in the
experimental animals from a disease probably due to infection with an
animal parasite.
Series 2. Daily feedings with azoa in oatmeal. Five white rats fed
with the mixture, a constant supply being kept in the cage. These
animals were picked rats freshly obtained from the dealer. One rat
died after seven days. It was heavily infested with lice. The azoa
organism could not be found in the blood. The rest remained well after
twenty-five days.
Series 3. Black tame mice, daily feedings. One of the five died after
seven days. The rest remained well after fourteen days.
These experiments indicate that azoa is not pathogenic for white rats
and black tame mice to a degree rendering it applicable for vermin
extermination on a practical scale, provided that its action is no
more pathogenic for the wild than for the tame species.
RATITE.
The manufacturers recommend a single feeding of this substance rather
than a continued exhibition of the virus.
Series 1. Five white rats starved twenty-four hours and then fed with
a mixture of ratite and oatmeal. Subsequent daily feedings with plain
oatmeal. Picked animals fresh from the dealer. One animal died after
twelve days; too much putrefied for further examination; had been
heavily infested with lice. The remaining rats are well after
twenty-five days.
Series 2. Five black tame mice fed as above. Three were found dead
after eighteen days and the other two after nineteen days. Further
experiments were not made, as putrefaction was too far advanced when
they were found. The room in which they were kept had been unusually
cold just before their death owing to a sudden and unexpected drop in
the external temperature.
Ratite does not appear to be very pathogenic for white rats. All the
five mice fed with ratite died in eighteen to nineteen days (much
longer than the advertised incubation period of the infection), but
their death could be reasonably attributed to unusual cold. This part
of the test is therefore invalidated except that the animals lived
considerably longer than would be expected from the literature
furnished by the manufacturers, which says that the effects of laying
the virus will be apparent in eight to ten days.
DANYSZ VIRUS.
Twelve tubes of Danysz virus were sent to the laboratory for
examination April 7 by the Independent Chemical Company, agent for
Danysz Virus Company (Limited). The label stated “Keep in a cool place
and at above temperature; use before May 15, 1909.”
The virus was kept at 15° C. until April 13, when it was turned over
to Passed Asst. Surg. W. H. Frost, who made the following tests:
One tube opened. Cultures made on two agar tubes were found to
correspond in cultural characteristics with the bacillus of Danysz
virus as generally described. The remainder of the tube prepared
according to directions in accompanying circular, using stale dry
bread 2 ounces and suspension of the culture in normal salt solution.
Series 1. Approximately equal parts, then fed to six white rats in
individual cages, they having not been fed for twenty-four hours
previously. Rats all ate greater part of infected food.
Five rats of series 1 died within five to seven days and were partly
eaten before being removed from the cage. The pathological changes in
all cases were chiefly enlargement and congestion of spleen and liver,
and in some cases inflammation of small intestine. In each case an
organism was obtained, usually in pure culture, from one or more
organs, corresponding culturally and morphologically with cultures
taken from original tube.
Series 2. April 14: Rats all ate greater part of infected food.
Transferred to large cage containing nine other white rats. Nine other
white rats exposed to infection by being placed in a large cage with
the rats of series 1. Four of the nine rats of this series died in
four to seven days after eating infected rats.
Pathological changes and results of cultures from internal organs the
same as with series 1. Autopsy and cultures impossible in one case,
where body was almost completely devoured.
Series 3. May 5: Three of the six surviving rats (one from series 1,
two from series 2) were placed in individual cages, deprived of food
for twenty-four hours, then fed each with one-third agar tube cultures
of Danysz virus (the same used in the original feeding). All three ate
practically all the virus given.
All three of these rats remain alive and well after two months.
Summary.—Series 1. Six rats each fed one-twelfth to one-sixteenth agar
culture Danysz virus. Five died within five to seven days.
Series 2. Nine rats exposed to infection by being placed in cage with
series 1. Four died within eight to twelve days after death of first
rat of series 1.
Series 3. Three of the surviving rats (1 from series 1 and 2 from
series 2) fed each with one-third agar tube of original Danysz virus
as used in series 1. None died.
TRANSATLANTIC RATIN.
A can of this substance labeled “Transatlantic ratin” was furnished by
the American agents representing the Bacteriological Laboratory,
Copenhagen, Denmark. The can bore the date January 26, 1909, and was
stated to be “effective for six months from date of production.”
On April 13, 1909, this sample was given to Passed Asst. Surg. W. H.
Frost for examination, and he obtained the following results:
April 13, 1909: Can of ratin opened with aseptic precautions. Contents
mixed with about equal bulk of clean fresh lard.
A portion of this about equal to one tablespoonful fed to each of six
white rats previously deprived of food for twenty-four hours. All the
rats ate some of the bait at once. Feeding at 2 p. m.
April 14: Five rats very sick, having convulsions; partially
paralyzed. One dead.
April 15: Three more rats found dead. Remaining 2 recovering.
The pathological change in all the above cases consisted chiefly of
intense congestion of intestines, both large and small.
Cultures from the original case of ratin, on agar, bouillon, and in
fermentation tubes, negative except staphylococcus in one tube.
Cultures taken from heart’s blood and other organs of the 4 dead rats
all negative, except in one case a growth of a staphylococcus
resembling _S. pyogenes citreus_.
April 20: Two rats fed on half agar slant culture of the
staphylococcus obtained from heart’s blood of rat No. 1. Result of
feeding negative after several weeks.
NOTE. The absence of a colon-like organism in this virus and the
rapid death of the animals with convulsions suggested a chemical
poison, which it is believed this can contained.—M. J. R.
EXPERIMENTS WITH MICRO-ORGANISMS FOR DESTROYING RATS, CONDUCTED BY THE
UNITED STATES BIOLOGICAL SURVEY.[AV]
Footnote AV:
This report was furnished by Dr. A. Hart Merriam, Director of the
Biological Survey.
RATIN.
The Biological Survey, Department of Agriculture, in cooperation with
the Bureau of Animal Industry, has experimented with “ratin.” The
material (ratin No. 2—labeled “Transatlantic ratin”) was furnished by
the American agents in New York. Although the agent claimed that this
was a bacterial preparation and that “it would kill for six
generations,” it proved to be a glucoside poison (probably squills)
and contained no bacteria of any kind. A number of experiments were
made with it, and it proved to be an effective rat poison. In some
instances the animals died within two hours after eating it, and in
two experiments all the animals fed died within twelve hours. In other
experiments, however, a considerable percentage of the affected rats
recovered, and subsequent attempts to kill them with ratin No. 2
failed. Some were immune to its effects and others too wise to eat it
a second time. More than a hundred rats were used in the experiments;
but the main object—to test the communicability of the disease caused
by ratin bacteria in healthy rats—failed, of course, since, as above
stated, the preparation experimented with contained no bacteria, but
was merely a vegetable poison. Before its character was fully
determined, 15 rats killed in the experiments were eaten by 5 healthy
rats; the latter were unaffected.
It should be noted that the labels on the tins containing
transatlantic ratin were misleading. The user was warned to open the
packages in dim light and to allow no moisture to come in contact with
the contents, as the bacteria were very sensitive to light and
moisture. The contents of the can were to be used at once. As a matter
of fact the contents of one can were exposed to severe drying in heat
and sunlight for four days and then soaked in water for two days.
Afterwards the preparation was fed to different rats for a further
period of four days, and its virulence was retained to the last.
The transatlantic ratin is in a solid medium, apparently bread and
molasses. Its keeping qualities are excellent, and it is an effective
poison for rats, but far too expensive for extensive use. A can
costing $1.50 is enough for only 15 baits.
Its harmfulness to domestic animals was not fully tested. Dogs and
cats refused to eat it and vomited it when it was forced upon them.
Several animals, including a dog, were killed by injections of the
poison in concentrated form.
A shipment of ratin No. 1 (the solid bacterial ratin, said to retain
its virulence for two months) was received June 4, 1909. This
preparation was dated May 8 and should have been still virulent. The
contents of a can mixed with milk was fed to 8 adult rats on June 7.
All of the baits were eaten, but no result followed. Cultures of the
bacteria showed strong growths of new colonies.
On July 6 the contents of another can were fed to 1 adult and 16 young
rats. One of the young was found dead on the morning of July 14.
Cultures were made from the dead rat, but the bacillus was not
recovered. Up to July 28 none of the other rats have been affected.
AZOA.
Several trials of azoa for the destruction of rats have come under the
observation of members of the Biological Survey. Experiments made in
the building occupied by the Interstate Commerce Commission were at
first promising, but from a second invoice of the virus no results
were obtained. In the buildings of the National Zoological Park 72
bottles of azoa were used, but the results were for the most part
negative. In a store in south Washington where this preparation had
been used the stench of dead rats was very strong, showing a measure
of success.
DANYSZ BACILLUS.
Some three years ago the Biological Survey, assisted by the Bureau of
Animal Industry, tested the efficiency of Danysz virus. In the
laboratory from 10 to 50 per cent of rats fed on the virus died. In
the field, however, results obtained were unsatisfactory. Only 1 dead
rat was found from which the bacillus was recovered. Experiments with
field mice gave better results. All the mice fed in confinement died,
and field experiments resulted in many dead mice from which the
bacillus was recovered.
EXPERIMENTS DURING THE SAN FRANCISCO PLAGUE OUTBREAK.[AW]
Footnote AW:
These experiments were made by Passed Asst. Surg. G. W. McCoy,
United States Public Health and Marine-Hospital Service, in 1907–8
during the plague campaign in San Francisco and here published for
the first time.
Several proprietary biological products sold as rat exterminators were
made the subject of seven experiments on wild San Francisco rats, for
the purpose of ascertaining whether they were efficient for the
purpose for which they were sold. Seventy-six rats were used in these
experiments. About 10 per cent died within a month and there was
considerable doubt as to whether all of the deaths that occurred were
due to the agent used.
The following is a brief statement of the work done with these agents.
In each case the rats used were wild _Mus norvegicus_, caught in San
Francisco.
RATIN NO. 1.
Made by the Bakteriologik Laboratorium, Copenhagen, marked: “Effective
two months from April 28, 1908.” The preparation comes ready for use
in the form of a moist, mealy mass. On May 28, about 6 ounces of the
material was fed to 12 rats. They all remained well until thirty days
after feeding them when the experiment was regarded as terminated.
DANYSZ VIRUS.
The Danysz Virus Company (Limited), of London, furnished a preparation
in the form of a culture on a slant of solid medium, said to be
gelatine. The tube was marked: “To be used before June 1, 1908.” The
contents of the tube, mixed with bread, according to directions, was
fed to 6 rats. On the twenty-first day but 4 rats remained, 2 having
died and been devoured by their companions. The 4 that remained were
chloroformed, as the cage was needed for other purposes. Post-mortem
examination showed them to be entirely normal.
RATITE.
Furnished by the Pasteur Vaccine Company, Chicago. This preparation is
in the form of a culture in a liquid medium, presumably broth. The
bottle was dated April 10, 1908, and the label stated that it should
be used within twenty days from date of preparation. On April 29,
1908, 9 rats were fed with about 6 ounces of the preparation, mixed
according to directions. The rats all remained alive and well, and
when chloroformed on June 1, 1908, presented no abnormality on
post-mortem examination. In another experiment the contents of a
bottle of ratite was fed to 6 medium-sized _Mus norvegicus_. None of
the animals died from the effects of the agent, and when they were
killed on the fifty-fifth day after the feeding were found to present
no lesions.
The remaining work was done with rat virus, sometimes called
“Mouratus.” It is made by the same concern that makes the ratite. The
rat virus comes in the form of a culture on a solid medium. The
contents of three tubes was fed to 6 rats on May 26, 1908. Three of
these rats died within thirty days. Only one was secured for
examination before it had been mutilated beyond the possibility of
making a satisfactory examination. This rat had a large yellow liver
and a very large, dark, firm spleen. These appearances were probably
due to the agent used and it is not unlikely that these 3 rats died
from its effect. It will be observed that a very large dose was given.
On another occasion four tubes of Mouratus were used for feeding 6
_Mus norvegicus_. One of the rats died on the fifteenth day, showing
at autopsy an enlarged granular spleen and a granular liver. The other
rats were alive and well at the end of thirty-four days when the
experiment was discontinued.
Subcultures on broth were made from this preparation on three
occasions, always well within the time limit on the label. The
cultures were incubated in the dark, at room temperature, for forty
hours on each occasion. Liberal amounts of the subculture were fed to
a total of 31 rats. At the end of thirty days, it was found that only
2 of these rats had died. The others were alive and apparently well.
One objection to these agents which I have not seen stated is the
following: The lesions caused by at least some of these members of the
paracolon group may readily be mistaken for the lesions of plague, or
it will perhaps be more accurate to say they give rise to lesions that
create in one’s mind a suspicion of plague infection, and I have had
to put many a rat to the guinea-pig test in order to make certain that
a Danysz infection was not associated with the infection of plague, or
that a Danysz rat was not a plague rat. Of course, this is of no
consequence except in a community where antiplague measures are being
taken, and an observer of limited experience who did not put a rat to
a pretty rigid test would probably call some plague infected when in
reality such is not the case.
In addition to the data set forth in this report, I have on several
occasions fed the tissue of rats dead of Danysz infection to other
rats, but have never succeeded in reproducing the disease. In other
words, I have had no success whatever in raising the virulence by
passage through animals.
OPINIONS OF OTHERS.
Kitasato,[AX] 1906, states that the typhoid bacillus of the rat, which
has been effectively used for killing field mice, has been found
useless for house rats (_Mus rattus_) and therefore they no longer
employ it.
Footnote AX:
Kitasato, S.: Combating plague in Japan. Philippine Journ. Sci.,
vol. 1, 1906, p. 465.
Melvin,[AY] 1908, reports that recently several new rat viruses were
investigated in the Bureau of Animal Industry, with the result that
the experiments clearly demonstrated the ineffectiveness and
unreliability of the preparations tested.
Footnote AY:
Melvin, A. D.: Report of the Chief of the Bureau of Animal Industry
for 1908. Washington, 1908.
Räbiger and Schwinning,[AZ] 1906, tested the culture discovered by G.
Neumann and prepared by the joint stock company “Ratin” at Copenhagen
by applying it to rat destruction. Of house rats 90 per cent died;
black rats 42.9 per cent; while horses, dogs, goats, sheep, fowls, and
pigeons suffered no harm. Of seven experiments practically carried
out, six showed very good results; in one favorable results were
absent, which agrees with the experiments made in Denmark. There it
was likewise found that in individual locally limited places the rats
were able absolutely to withstand the infection of ratin.
Footnote AZ:
Räbiger and Schwinning: Versuche mit Ratin, einem neuen Ratten
tötenden Bacillus. Mitth. d. deutsch. Landw.-Gesellsch., 1906, No.
18. Rev. by Ehrenberg in Centblt. f. Bakt., 2. Abt., vol. 18, 1907,
p. 375.
Räbiger,[BA] 1905, states that experiments with Loeffler’s mouse
typhus bacillus and the bacillus of Danysz virus have been carried to
the conclusion that these bacterial preparations must be characterized
as practically worthless.
Footnote BA:
Räbiger, H.: Ueber Versuche zur Vertilgung der Ratten durch
Bakterien. Landw. Woch. f. d. Prov. Sach., 1905, p. 142. Rev. by
Stift in Centblt. f. Eakt., 2 Abt., vol. 15, 1905, p. 86.
In 1903 Neumann discovered in Denmark a rat-killing bacillus, which
has been placed on the market by a society under scientific control
under the name of “ratin.” Feeding experiments with this bacillus were
tried under conditions as nearly natural as possible upon white mice,
gray house mice, long-tailed field mice, and gray rats. The experiment
animals were fed with cubes of white bread impregnated with virulent
cultures. White mice show the least power of resistance, since they
die within six days; house mice died in six to nine days; the greater
part of the rats died from the sixth to the sixteenth day after
feeding; a small percentage lived. The long-tailed field mice, which
are shown to be insusceptible to Loeffler’s bacillus, also remained
perfectly healthy after repeated feedings with bread infected with
ratin.
Brooks,[BB] 1908, reports the results of tests made with azoa on rats
and mice, both in captivity and at large, but without any apparent
discomfort to the animals. One of the tests is described as follows:
Footnote BB:
Brooks, Fred E.: Notes on the habits of mice, moles, and shrews. A
preliminary report. Bull. 113, W. Va. Univ. Agric. Exper. Sta.,
Morgantown, W. Va., Jan., 1908.
A supply of the azoa was obtained direct from the laboratories of
the manufacturers. On July 27, 1907, while the material was yet
fresh, three young Norway rats were caught and kept confined in a
large wire rat trap. Beginning with the date given, and for a period
of forty days thereafter, azoa was fed to the rats at intervals of a
few days until ten 75-cent bottles had been consumed. The rats ate
the cracked grain with which the virus was mixed very readily, and
other food was denied them each time the azoa was given until every
particle was eaten. At the end of the forty days the rats were still
apparently in a healthy condition, and were removed from the trap
and killed with a club.
Thompson,[BC] 1906, states that three laboratory attempts have been
made to destroy rats with imported strains of Danysz rat virus without
success. Danysz having arrived at Sydney to study a similar method of
destroying rabbits, the opportunity was taken of making a further
attempt under his supervision with virus which had been imported and
subsequently increased to the requisite degree of virulence, and had
been placed at Thompson’s disposition. The grounds of the Gladesville
Asylum, a large institute for the insane, were chosen for the tests,
which were conducted by Dr. R. J. Millard.
Footnote BC:
Thompson, J. Ashburton: Report of the Board of Health on plague in
New South Wales, 1906. On a sixth outbreak of plague at Sydney,
1906. Legislative assembly, N. S. W., 1907.
Millard summarized his result by stating that they can not be
considered a satisfactory demonstration of the efficacy claimed for
the Danysz virus. The results indicate a rapid loss of virulence,
which must be obviated if this virus is to be of utility for rat
destruction.
Again, in 1907, during the seventh outbreak of plague in Sydney,
Thompson[BD] had Millard test the preparations known as azoa and
ratin. The laboratory results with these preparations were similar to
those made by other investigators. Experiments made upon the ship
_Hartfield_ with azoa produced no considerable epizootic. The fatality
among such rats as were infected was small. The practical tests with
azoa upon several areas along the harbor front also resulted in
disappointment.
Footnote BD:
Thompson, J. Ashburton: Report of the board of health on plague in
New South Wales, 1907. On a seventh outbreak of plague at Sydney,
1907. Legislative Assembly, N. S. W., 1908.
The tests made with ratin upon the bark _Quilpe_ produced no epizootic
among the rats, and of the rats caught none of them showed infection;
and the field experiment at Gladesville also resulted negatively so
far as dead or sick rats were concerned. Nevertheless, there was
apparently considerable diminution in the rat population of this area.
Foster,[BE] 1908, reports unfavorably upon the results of tests made
of some of these rat viruses. Laboratories were opened for the use of
different parties who wished to make tests. The tests were conducted
under their own supervision. The rats which were not fed on anything
but grain died as freely as those that had been fed on azoa. So far as
this preparation is concerned Foster states that it is absolutely
useless to depend upon it.
Footnote BE:
Foster, N. K.: The danger of a general plague infection in the
United States. Proc. Confer. State and Prov. Boards of Health of N.
America, 1908, p. 15.
Several reports are found in print in which the rat virus was laid out
in certain localities and shortly afterwards the rats disappeared—at
least no more were noticed. Such observations are apt to be
misleading, for rats are migratory. They come and go, especially when
disturbed. Further, it is doubtful, as far as plague is concerned,
whether it is desirable to drive the rats away, for they may thus
scatter the infection.
S. S. Mereshkowsky and E. Sarin[BF] have recently studied ratin II,
put out by a Copenhagen firm—“Bakteriologisches Laboratorium Ratin.”
The label upon the can of ratin II states that it is a bacterial
culture, which produces in rats an infectious and fatal disease,
killing them in two to eight days. The samples used by the authors
were obtained as needed from the St. Petersburg representative of the
firm. Feeding experiments carried out with gray rats (_Mus decumanus_)
showed that the rapidity and severity of the symptoms was proportional
to the amount ingested. No positive results were obtained from the
bacteriological examination of the bodies.
Footnote BF:
Ueber das Ratin II. Centralb. für Bakt. Parstk. u. Infectsk.
Originale. Bd. 51. Heft 1. July 17, 1909, p. 6.
The ratin itself was sometimes found to be sterile, sometimes found to
contain several varieties of bacteria and fungi, but no one variety
was constantly present.
The potency of the ratin was not altered by exposure to 100° C. for
one hour or 120° C. for five minutes. It was destroyed, however, by
burning to an ash.
Identical poisonous results were obtained upon rats by feeding them
with “Scilla maritina cum bulbo rubro.”
Microscopical examination disclosed a small portion of a lamella,
identified as belonging to the Liliaciæ, to which family squill
belongs.
The authors conclude that ratin II is not a bacterial culture, but a
poison rendered more dangerous to persons and domestic animals by the
misleading statements of its makers.
PATHOGENICITY FOR MAN.
Loeffler[BG] rather took it for granted at first that his _Bacillus
typhi murium_ was harmless for man. In order to remove the fears of
the peasants in his campaign against the field mice in Thessaly he fed
pieces of bread impregnated with the cultures to chickens, pigeons,
dogs, hogs, horses, asses, sheep, and goats. No ill effects resulted.
Further, some of the men who were distributing the prepared virus ate
pieces of the infected bread in the presence of all and, it appears,
suffered no ill effects.
Footnote BG:
Loeffler, F.: Die Feldmausplage in Thessalien und ihre erfolgreiche
Bekämpfung mittels des Bacillus typhi murium. Centblt. f. Bakt.,
vol. 12, 1892, p. 1.
Up to this time Loeffler had made no human experiments, but thought it
improbable that his bacillus was harmful to man. He considered this
view confirmed by the fact that he and his companions and still more
so the peasants, handled large quantities of the virus without
thorough disinfection of their hands and suffered no untoward effects.
Since that time, however, several mishaps have occurred. Instances of
serious sickness and even death have been attributed to infection with
the bacterial virus used for the destruction of rats.
Further, there is practically no difference between the _Bacillus
typhi murium_ and the para-typhoid bacillus which is the well-known
cause of meat poisoning, and the _Bacillus enteridion_ of Jarbues,
which is associated with intestinal disorders.
It is true that persons have purposely partaken of the rat virus to
prove that it is harmless to man; but it must be remembered that
persons have partaken of cultures of cholera, typhoid, and other
bacteria without apparent injury to themselves. The flora and
condition of the gastro-intestinal tract, the amount and virulence of
the infection, and other conditions (“Y” and “Z” of Pettenkofer) play
an important rôle in the production of these diseases.
The following references from the literature give the instances in
which the _B. typhi murium_, or similar rat viruses, have been held
responsible for the disease in man:
Trommsdorff[BH] carefully studied 13 suspected cases near Munich in
early May, 1903. Nine of these came into direct contact with the
virus, three ate and associated with these, and the remaining one only
smelled of the virus. One died from vomiting and severe diarrhea. The
illness, which set in usually two days after contact with the virus,
was for the most part simple diarrhea of two to seven days’ duration
(two to eight stools daily); in only three or four cases was there
vomiting. The one fatal case seemed due to a confusing chain of
circumstances, gross dietetic and alcoholic excesses in a weak,
emaciated, presumably phthisical man whose three brothers had died of
phthisis. One man, case No. 2 in the table, known to have eaten three
pieces of infected bread, suffered only with a mild diarrhea.
Footnote BH:
Trommsdorff, R.: Ueber Pathogenität des Löfflerschen
Mäustyphusbazillus beim Menschen. Münch. med. Woch., vol. 50, 1903,
p. 2092.
In all cases errors of diet could be proven, and diarrhea was not
uncommon at that season. The same physician attended during this
period ten other cases of similar diarrhea in the vicinity having
nothing to do with rat virus. The stools, however, did not have the
same pathogenicity for mice, guinea pigs, or rabbits.
Trommsdorff specially points out the fact that the bacillus of mouse
typhoid can multiply vigorously in the human intestine. It demands
greater caution in the application of the cultures and more careful
supervision over their use.
Finally, attention is invited to the fact that, contrary to the usual
custom, the cultures of rat virus here used had been grown on milk,
which might account for the increased virulence.
The following table gives a brief summary of ten cases with the
results of the agglutination tests:
_Agglutination tests with serum of recovered cases, May 17, 1908._
──────┬─────────────────────────┬────────┬─────────────────────────────
Case. │ How infected; symptoms. │Strains.│ Serum dilutions.
„ │„ │„ │¹⁄₂₀ │¹⁄₄₀ │¹⁄₆₀ │¹⁄₁₀₀│¹⁄₂₀₀
──────┼─────────────────────────┼────────┼─────┼─────┼─────┼─────┼─────
1 B. │(From this case stool 2.)│A │ + │ + │ + │ ± │ 0
K. │ Laid rat poison │ │ │ │ │ │
│ 5–2,5–5; some days │ │ │ │ │ │
│ later diarrhea; later │ │ │ │ │ │
│ vomiting; convalescence│ │ │ │ │ │
│ and recovery May 10. │ │ │ │ │ │
„ │„ │B │ + │ + │ + │ ± │ 0
„ │„ │C │ + │ + │ + │ ± │ 0
„ │„ │D │ + │ + │ + │ + │ ±
──────┼─────────────────────────┼────────┼─────┼─────┼─────┼─────┼─────
2 K. │Ate three pieces of │A │ + │ 0 │ 0 │ 0 │ 0
E. │ infected bread May 2; │ │ │ │ │ │
│ mild diarrhea several │ │ │ │ │ │
│ days. │ │ │ │ │ │
„ │„ │B │ + │ ± │ 0 │ 0 │ 0
„ │„ │C │ 0 │ 0 │ 0 │ 0 │ 0
„ │„ │D │ + │ ± │ 0 │ 0 │ 0
──────┼─────────────────────────┼────────┼─────┼─────┼─────┼─────┼─────
3 H. │Brought the virus April │A │ + │ 0 │ │ │
B. │ 28; perhaps touched it;│ │ │ │ │ │
│ next day diarrhea and │ │ │ │ │ │
│ vomiting; recovery │ │ │ │ │ │
│ after several days. │ │ │ │ │ │
„ │„ │B │ + │ 0 │ │ │
„ │„ │C │ + │ 0 │ │ │
„ │„ │D │ − │ − │ − │ − │ −
──────┼─────────────────────────┼────────┼─────┼─────┼─────┼─────┼─────
4 G. │Father of man that died; │A │ + │ + │ + │ + │ 0
S. │ laid virus; two days │ │ │ │ │ │
│ later mild diarrhea for│ │ │ │ │ │
│ one or two days. │ │ │ │ │ │
„ │„ │B │ + │ + │ + │ + │ 0
„ │„ │C │ + │ + │ + │ 0 │ 0
„ │„ │D │ + │ + │ + │ + │ ±
──────┼─────────────────────────┼────────┼─────┼─────┼─────┼─────┼─────
5 J. │On April 27 laid virus; 2│A │ ± │ 0 │ 0 │ 0 │ 0
K. │ days later diarrhea for│ │ │ │ │ │
│ several days. │ │ │ │ │ │
„ │„ │B │ ± │ 0 │ 0 │ 0 │ 0
„ │„ │C │ ± │ 0 │ 0 │ 0 │ 0
„ │„ │D │ − │ 0 │ 0 │ 0 │ 0
──────┼─────────────────────────┼────────┼─────┼─────┼─────┼─────┼─────
6 J. │Laid virus April 27; two │A │ 0 │ 0 │ 0 │ 0 │
N. │ days later had diarrhea│ │ │ │ │ │
│ for several days. │ │ │ │ │ │
„ │„ │B │ + │ + │ + │ ± │
„ │„ │C │ 0 │ 0 │ 0 │ 0 │
„ │„ │D │ + │ + │ + │ ± │
──────┼─────────────────────────┼────────┼─────┼─────┼─────┼─────┼─────
7 G. │“Held” the virus April │A │ + │ + │ + │ + │ ±
I. │ 28. Next day diarrhea │ │ │ │ │ │
│ for four days. │ │ │ │ │ │
„ │„ │B │ + │ + │ + │ + │ ±
„ │„ │C │ + │ + │ + │ + │ ±
„ │„ │D │ − │ − │ − │ − │ −
──────┼─────────────────────────┼────────┼─────┼─────┼─────┼─────┼─────
8 H. │Ate and associated with │A │ + │ + │ 0 │ │
R. │ persons who handled │ │ │ │ │ │
│ virus; diarrhea several│ │ │ │ │ │
│ days. │ │ │ │ │ │
„ │„ │B │ + │ − │ 0 │ │
„ │„ │C │ + │ ± │ 0 │ │
„ │„ │D │ − │ − │ − │ │
──────┼─────────────────────────┼────────┼─────┼─────┼─────┼─────┼─────
9 K. │Associations as case 8; │A │ + │ + │ + │ + │
S. │ headache several days │ │ │ │ │ │
│ and loss of appetite. │ │ │ │ │ │
„ │„ │B │ + │ + │ + │ + │
„ │„ │C │ + │ ± │ 0 │ │
„ │„ │D │ − │ − │ − │ − │ −
──────┼─────────────────────────┼────────┼─────┼─────┼─────┼─────┼─────
10 │Associations as case 8; │A │ 0 │ 0 │ 0 │ 0 │
│ diarrhea for eight │ │ │ │ │ │
│ days; vomiting several │ │ │ │ │ │
│ days. │ │ │ │ │ │
„ │„ │B │ + │ + │ + │ ± │
„ │„ │C │ 0 │ 0 │ 0 │ 0 │
„ │„ │D │ + │ + │ + │ ± │
──────┴─────────────────────────┴────────┴─────┴─────┴─────┴─────┴─────
A = Strain from Loeffler.
B = Strain from market virus.
C = Strain from stool 1 (fatal case).
D = Strain from stool 2 (case 1 of table).
− = No test made.
0 = Negative.
± = Slight.
Controls = Serum of five normal persons tested as above; gave in no
case agglutination higher than 1 : 20.
The attending physician, noting that most of his patients had come
into recent contact with rat virus (_B. typhi murium_) and suspecting
that to be responsible, sent specimens of stools to the Hygienic
Institute at Munich, where they were carefully examined with reference
to this subject.
Organisms identical with Loeffler’s _B. typhi murium_ were isolated
from the two stools examined and these cultures were compared with and
conformed with a culture of _B. typhi murium_ obtained from Loeffler
and also a culture from the virus on the local market.
Two guinea pigs injected with cultures from the two stools gave, after
the second injection, serum which agglutinated all the above organisms
1:200. A mouse typhoid serum obtained from Loeffler agglutinated all
the above strains distinctly in dilutions 1:640 and slightly in
1:1280.
In conclusion, the author considers three possibilities: 1. The mouse
typhoid bacillus was the cause of the illness. 2. The bacillus was
accidentally present, having no part in the production of the
symptoms. 3. The bacillus was able to multiply only in case
pre-existing intestinal trouble; then, however, causing the
inflammation.
The case of Mayer, who became infected during the course of some
laboratory experiments, is particularly instructive.
During an epidemic of mouse typhoid among his laboratory mice,
evidently spread from some inoculated mice by ants, Mayer[BI] who had
personally handled the infected mice and their cages, became sick July
15, just seven days after the first appearance of the ants and after
the observed rise in virulence of the mouse typhoid among the mice.
His clinical history is as follows:
Footnote BI:
Mayer, Georg: Ueber die Verschleppung typhöser Krankheiten durch
Ameisen und die Pathogenität des Loeffler’schen Mäusetyphusbazillus
für den Menschen. Münch. med. Woch., vol. 52, 1905, p. 2261.
July 15: Weakness, epigastric pain, obstipation, temperature 37.7,
pulse 90.
July 16: Slight diarrhea, increase of pain in region of trans-colon,
temperature 38.3, pulse 98.
July 17: Diarrhea continued, pains increased—severe, chill in evening,
temperature 39.1, pulse 102.
July 18: Obstipation, symptoms worse, chill again in evening,
temperature 39.4, pulse 104.
July 19: Symptoms better, stools from purgative, evening temperature
36.9, pulse 68.
July 20: Left bed. Temperature and pulse normal, but weakness and
slight epigastric pains continued till August 7.
Patient’s serum agglutinated as follows:
──────────────────────────┬──────────────┬──────────────┬──────────────
│ Typhoid. │ Paratyphoid. │Mouse-typhoid.
──────────────────────────┼──────────────┼──────────────┼──────────────
July 23 │ 1–50+│ 1–50+│ 1–250+
August 7 │ 1–50+│ 1–50+│ [BJ]1–100+
August 16 │ 1–50+│ 1–50+│ 1–50 +
──────────────────────────┴──────────────┴──────────────┴──────────────
Footnote BJ:
Slight
The bacillus of mouse typhoid was isolated from the patient’s stools
July 21 and 23. Negative results thereafter. Examinations continued a
month.
Same organism isolated from urine July 21. Negative thereafter.
The author concludes that the _B. typhi murium_ is able to cause in
man a rather severe acute illness of short duration.
Shibayama[BK] gives the following report of outbreaks of human
infection that have come to his knowledge in Japan, where
mouse-typhoid virus has been used in considerable quantities.
Footnote BK:
Shibayama, G.: Ueber Pathogenität der Mäusetyphusbazillen für den
Menschen. Münch. med. Woch., May, 1907, p. 979.
_Outbreak 1._ In April, 1905, in a village of the Province of Saitama,
30 people became ill and 2 died with severe gastro-intestinal
symptoms. Outbreak investigated by Dr. H. Sezuki, district medical
officer, formerly of the Tokio Institute for Infectious Diseases.
It was found that all the 30 people had partaken of a dish of cooked
vegetables served at a meeting of the town council, and that for
application of sauce to these vegetables (after cooking) a wooden
vessel had been used which two days before had been used for mixing
mouse-typhoid virus with meal, without subsequent cleansing or
sterilization.
The symptoms came on within twelve to forty-eight hours thereafter
(usually twenty hours), chill or chilly sensations, rise of
temperature to 38° or 39° C., or even to 40° C.; face flushed; pulse
accelerated; great weakness; thirst, nausea, colicky pains in abdomen
followed by severe diarrhea and vomiting. In general, the fever and
diarrhea lasted two or three days; but malaise, anorexia, weakness,
and mucous stools persisted for several days. The more severe cases
showed choleraic symptoms of collapse. Two persons died in spite of
medical treatment—a 6-year old boy and a man of 43, on the second and
third day, respectively.
From the intestinal contents of these two cases, from the stools of
several other cases, and from the remnants of the dish of vegetables
in the wooden bowl an organism was isolated, which was demonstrated to
be identical with the bacillus of mouse typhoid.
These results were confirmed at the Tokio Institute for Infectious
Diseases by Shibayama, by biological and immunizing tests.
_Outbreak 2._ On December 7, 1905, a peasant of a village in the
Province of Miyaki brought home some mouse virus mixed with meal in
cakes. This being mistaken for “mochi” was eaten about 2 p. m. the
next day by two little girls, 3 and 8 years old, respectively, and
their grandfather, 61 years old.
The man and the 8-year-old girl became sick at 9 p. m. the same day
and the other child at about 3 p. m. on December 9. The symptoms in
all cases were those of severe gastro-enteritis, as described under
outbreak 1.
The man died December 12, the 8-year-old child died on the 10th; the
3-year-old child recovered after several days’ illness. These three
alone ate of the virus and no other persons in the house became sick.
No bacteriological examination was practicable.
_Outbreak 3._—In a village of the Province of Iskawa, on April 22,
1906, a lot of rat poison was prepared by mixing agar cultures of the
mouse-typhoid bacillus with meal and water in a large wooden bowl.
On April 24 there was a festival in the village at which about 170
persons were served with 240 pounds of rice, which, after being
cooked, was kneaded into cakes in a wooden bowl. About 80 pounds of
this rice was so kneaded in the bowl previously used for preparing the
rat poison. Twenty to twenty-four hours later 120 people who had eaten
of the rice became ill with the already described symptoms of
gastro-enteritis, of mild type among the strong but severe among the
children and old people. Eighty-nine cases came under medical
treatment. There were no deaths, but a number of cases were confined
to bed for a week or more; mild cases recovered in one to three days.
No bacteriological examination was made, but the physicians and town
officials were unanimously of the opinion that the rat virus was the
cause of the outbreak.
_Outbreak 4._—A peasant of the province of Niigata brought home on May
14, 1906, some rat virus (cultures of mouse-typhoid bacilli mixed with
meal) which he laid away. Two of his grandchildren—a boy of 5 and a
girl of 7—together with the 4-year-old daughter of a neighbor, found
and ate the rat virus. The next day all three children became ill with
severe gastro-enteritis, of which the 4-year-old child died on the
third day. The others recovered after several days of medical
treatment.
_Outbreak 5._—On May 16, 1906, a peasant in the province of Jamagata
brought home some rat virus (6 c. c. cultures of mouse-typhoid
bacillus mixed with meal), which was accidentally mixed with the feed
given to a healthy horse next morning. The same evening the horse
showed loss of appetite and appearance of sickness. Within two days he
developed a severe enteritis, of which he died on the seventh day. The
body was buried, but was dug up in the night by a laborer who cut off
the hind quarters, took them home, and distributed the meat among
friends and neighbors.
Within three days 34 persons who had eaten of this meat became ill
with symptoms of severe gastro-enteritis. A 72-year-old man died after
five days; the others recovered in three to eleven days.
This outbreak was investigated by Dr. H. Segawa, a medical officer of
the province and former member of the institute at Tokyo, who isolated
from the remains of the horseflesh by plate cultures and animal
inoculations, an organism identical with the bacillus of mouse
typhoid. A culture was sent to Shibayama, who carefully verified it
(details not given).
Shibayama concludes: In all cases the close relationship between the
bacillus of mouse typhoid and the illness was established; and he
thinks this organism must be accepted as the direct cause of the
outbreaks.
Referring to Loeffler’s uniformly negative human experiments, he calls
attention to known cases where men have taken virulent cultures of
typhoid, diphtheria, etc., without infection. According to many
bacteriological investigations, _B. typhi murium_ is identical with
the bacillus of enteritis. If it is proven that the latter is a cause
of acute gastro-enteritis then the conclusion is likewise justified
that the _B. typhi murium_ is frequently pathogenic for man, causing
an acute gastro-enteritis.
Fleischanderl[BL] a reports six cases of illness—three severe and
three mild—occurring in his practice in the latter part of April,
1908, presenting the following symptoms: Onset with rapidly increasing
body pains, followed in a few hours by diarrhea, rise of temperature,
and general prostration; in the next two or three days aggravation of
the symptoms, fever (39° to 40° C.), copious diarrhea, vomiting (in
one case), severe body pains, vertigo, and considerable prostration.
Symptoms abated quickly in a few days, leaving considerable
prostration, convalescence requiring two weeks in one case. In the
less severe cases there was no fever, and the other symptoms were
generally milder.
Footnote BL:
Fleischanderl, Fritz: Mitteilung über einige Krankheitsfälle,
hervorgerufen durch Mäustyphusbazillen. Munch. med. Woch., vol. 56,
Feb., 1909, p. 392.
The simultaneous appearance of these and other similar rumored mild
cases among the neighbors (about 20 in all) pointed to a common cause.
It was found that three of the six cases were in people who had
handled mouse-typhoid cultures the day before their illness, taking no
precautions to avoid infection.
The other three occurred in a family which, on the day before the
onset of the illness, had drunk raw milk obtained from a house where
the rat virus had been used shortly before, and only three members of
the family who drank the milk became ill.
In order to prove the etiology of these cases Fleischanderl, who had
never suffered any intestinal troubles, had had nothing to do with any
case of typhoid fever for a year, and was in excellent health, took a
culture of the mouse-typhoid bacillus as used in the neighborhood,
rubbed a glass rod over the surface, washed it off in a glass of
water, and drank this before breakfast on the morning of May 3.
In twenty-two hours he experienced mild, increasing body pains,
followed within a few hours by diarrhea, and a few hours later by
slight chill, rise of temperature to 38.2, pulse 106, severe pains in
body, and feeling of great weakness.
May 4, 9 p. m.: Temperature 39.2° C., pulse 120. Height of symptoms.
May 5: Temperature 38.2° to 38.5° C., pulse 106 to 120. Other symptoms
continued.
May 6: Temperature and pulse normal. All symptoms disappeared except
weakness, which lasted two days.
Bacteriological investigations conducted by Herbert Berger in the K.
K. Serotherapeutischen Institut and by Doctor Reichel, assistant in
the Hygienic Institute of the University of Vienna, follow:
From the stools of one of the patients infected from milk an organism
was isolated which, injected into mice (1 c. c. emulsion of
forty-eight-hour culture), killed them in two to five hours. Mice
infected by eating these dead mice died in thirty to forty-eight
hours.
Control mice inoculated similarly with a culture of the market
mouse-typhoid virus died in twenty to thirty hours, while the mice
infected through eating these died after three to four days.
The following strains were used for cultural agglutination tests:
A. From stools of patient infected from milk.
B1. Market virus used in injecting mice.
B2. Market virus taken by author.
C25. From stools of author twenty-five hours after infection.
C55. From stools of author fifty-five hours after infection.
LL. Stock culture of Loeffler’s mouse-typhoid bacillus.
LP. Stock culture of para-typhoid bacillus.
All organisms (A-C55) were demonstrated as motile bacilli, not
liquefying gelatine, not forming lactic acid, and forming gas from
dextrose.
The serum of a rabbit after two injections of LL agglutinated LL and
LP in dilution of 1:1280, did not agglutinate A, B1, B2, C25, and C55.
Serum of rabbit after one injection of B2 agglutinated in 1:320
dilution A, B1, B2, C25, C55, and LL; did not agglutinate LP.
Serum of rabbit after one injection of C25 gave exactly similar
results.
Doctor Reichel considers it proven that the organisms A to C55 are
undoubtedly identical with Loeffler’s bacillus of mouse typhoid, and
distinct from para-typhoid bacilli. The author considers it proven
that this bacillus was the sole cause of the cases of enteritis
observed.
Recently Mallory and Ordway[BM], in a paper read before the American
Association of Pathologists and Bacteriologists held in Boston,
reported that lesions analogous to the early stages of typhoid lesions
may be produced in rats by the use of Danysz virus.
Footnote BM:
Mallory, F. B., & Ordway, T.: Lesions produced in the rat by a
typhoid-like organism (Danysz virus). Journ. Am. med. assn., vol.
52, May 1, 1909, p. 1455.
In view of these facts the statements of some of the advertising
matter of certain rat viruses call for revision.
REFERENCES TO THE LITERATURE.
Loeffler,[BN] 1889, gives an account of two spontaneous outbreaks
among the mice kept at the Hygienic Institute at Griefswald. It was
from these animals that he obtained and described the original _B.
typhi murium_. He determined that the infection was by ingestion and
that the organism was especially virulent for field mice. He described
the organism in detail and also the lesions.
Footnote BN:
Loeffler, F.: Ueber Epidemieen unter den im hygienischen Institute
zu Griefswald gehalten Mäusen und über die Bekämpfung der
Feldmäusplage. Centblt. f. Bakt., Orig., vol. 11, 1898, p. 129.
Laser,[BO] 1892, reports that on the morning of February 6, 1892, 70
of the 76 field mice (_Mus agrarius_) used as experiment animals in
the Hygienic Institut at Königsberg were found dead. A small bacillus
twice as long as broad, displaying a very lively specific motility,
was isolated from the spleen. It was tested upon animals and all the
results compared with Eisenberg’s tables and found to be closely
allied to the bacillus of ferret plague (Ebert-Schummelbusch), to the
bacillus of American swine plague (Billings), and to that of French
swine plague (Chantamesse and Cornil).
Footnote BO:
Laser, Hugo: Ein neuer für Versuchsthiere pathogener Bacillus aus
der Gruppe der Frettschen-Schweinseuche. Centblt. f. Bakt., Orig.,
vol. 11, 1892, p. 184.
Mereshkowsky,[BP] 1893, isolated an organism at the Royal
Bacteriological Institute at St. Petersburg from a stock of Zisel
(_Spermophilus musicus_) among which a spontaneous epizootic had
occurred. The author found this culture to be virulent for domestic
and field mice.
Footnote BP:
Mereshkowsky, S. S.: Ein aus Zieselmäusen ausgeschiedener und zur
Vertilgung von Feld-resp. Mäusen, geeigneter Bacillus. Centblt. f.
Bakt., Orig., vol. 17, 1895, p. 742.
Zupnik,[BQ] 1897, states that Joseph, of the Agricultural Institute of
Breslau, in 1882 originated the use of favus fungus for the
destruction of mice. Zupnik tested _B. typhi murium_ and Danysz virus
upon mice. No experiments with rats.
Footnote BQ:
Zupnik, Leo: Ueber die pratische Verwendbarkeit der Mäuse bacillen
inbesondere des Loeffler’schen _Bacillus typhi murium_. Centblt. f.
Bakt., Orig., vol. 21, 1897, p. 446.
Issatschenko,[BR] in 1898, described briefly a bacillus obtained by
him from gray rats. Recent investigation showed this bacillus to be
very virulent for rats and mice, but harmless for the different
species of domestic animals. Four hundred and forty-three experiments
were made upon rats with pure cultures of the bacillus combined with
dough and fed to the rats. He gives a table showing that the mortality
occurred in 431 rats at an average of ten and one-half days. The
greatest mortality occurred during the first fifteen days (84.2 per
cent), with the greatest number on the seventh day (20.1 per cent).
Footnote BR:
Issatschenko, B.: Untersuchungen mit dem für Ratten pathogenen
Bacillus. Centblt. f. Bakt., Orig., vol. 31, 1902, p. 26.
Danysz,[BS] 1900, isolated a cocco-bacillus during an outbreak of
spontaneous disease amongst field mice which presented the general
characteristics of the colon bacillus and to this extent resembled
Loeffler’s bacillus (_B. typhi murium_), and which from the beginning
exhibited some pathogenicity for gray rats (_M. decumanus_). Of ten
such rats fed upon a culture of this organism, two or three died,
while others that had fallen sick recovered and the same remained
well. This small mortality offered some hope that it would be possible
to increase the virulence of the bacillus by ordinary methods; that
is, passing it from rat to rat. It was found, however, that the
opposite was true; the virulence was always weakened by this process
regardless of the method of administration. Thus in every series the
first culture killed the animals in seven to twelve days; occasionally
after one or two passages five to seven days; but subsequent passages
decreased the virulence so that none died.
Footnote BS:
Danysz, J.: Un microbe pathogène pour les rats (_Mus decumanus_ et
_Mus rattus_) et son application à la destruction de ces animaux.
Ann. Inst. Pasteur, 1900, vol. 14, p. 193.
The general result is that it is difficult to maintain the virulence
of the cocco-bacillus of the rat or to increase it when it is found to
be small. It can only be effected by constantly making a large number
of experiments and frequently testing the virulence of the culture.
Danysz succeeded in keeping up a supply of cultures of sufficient
strength for eight years. In 60 per cent of the operations where this
culture has been used it has been successful in causing the absolute
disappearance of the rats. In 15 per cent the result was entirely
negative, and in the remaining 25 per cent there was a large
diminution.
Oettinger,[BT] in 1903, increased the virulence of the Danysz bacillus
by growth in an egg rendered alkaline after the method previously
introduced by Wiener.
Footnote BT:
Oettinger, M.: Ueber die Wienersche Methode zur Virulenzsteigerung
der Danysz Bazillen. Munch. med. Woch., vol. 1, 1903, p. 324.
Pfreimbtner,[BU] 1904, sees the reason for a partial failure in the
application of Loeffler’s bacillus to the destruction of field mice.
In the use of a solid medium (agar-agar), upon which the bacterial
cultures only grow upon the surface, too few bacteria are transferred
to the pieces of bread, and consequently too few virulent bacteria are
consumed by the mice. An active infection depends not upon the
existence of virulent bacteria, but rather upon the entrance of a
definite number of virulent bacilli.
Footnote BU:
Pfreimbtner, J.: Erfahrung über des Loeffler’schen
Infektionsverfahren zur Bekämpfung der Mäuseplage in einer neuen Art
der Anwendung. Fühlung’s landw. Zeit., 1904, p. 619. Rev. by
Schander in Centblt. f. Bakt., 2. Abt., vol. 15, 1905, p. 502.
The author used skimmed milk as a nutrient medium and describes a
series of 9 experiments and gives an estimate of the cost of the
process with the use of milk instead of agar. The advantage of the use
of milk is in the greater certainty of the results and cheapness as
compared with other methods. The bread cubes impregnated with skimmed
milk were well taken by the mice and desiccation of the cultures,
which not infrequently occurs in the use of more solid media, is
excluded. Notwithstanding the excessive thinning, the liquid still
contains many virulent bacilli. The washing out of bacilli after rain
is slightly less possible as in the use of the more solid media. The
action of light, where the bread cubes contain many bacilli, is
insignificant, and hence the carrying out of the process in the
daytime is made possible. Milk is easily obtained and the thinning and
application less bothersome. Finally the author expresses himself
against the view that the _B. typhi murium_ causes serious diseases in
man.
Teichert,[BV] 1905, speaks of Loeffler’s mice typhus bacillus and
Pfreimbtner’s method of growing it upon sterilized skimmed milk. A
number of experiments carried out at the bacteriological laboratory of
the Vreschen experiment station shows the utility of Loeffler’s
bacillus for the destruction of house and field mice. The long-tailed
field mouse was, on the other hand, not harmed by it.
Footnote BV:
Teichert: Die mechanischen, chemischen und bacteriellen Kampfmittel
gegen Ratten und Mäuse. 2. Teil: Die Bekämpfung der Mäuse. Fühlung’s
landw. Zeit., 1905, No. 16. Rev. by Ehrenberg in Centblt. f. Bakt.,
2. Abt., vol. 15, 1905, p. 503.
Bahr,[BW] 1905, gives a complete and satisfactory summary of the
literature upon the subject of the destruction of rats and mice with
bacteria, including original work of his own.
Footnote BW:
Bahr, L.: Ueber die zur Vertilgung von Ratten und Mäusen benutzten
Bakterien. Centblt. f. Bakt., Orig., vol. 39, 1905, p. 263.
Zielander,[BX] 1908, obtained fairly good results with Danysz virus in
the laboratory, also with ratin. No fixed tests were recorded.
Footnote BX:
Zielander: Der Rattenbacillus als Rattenvertilgungsmittel. Arb. a.
d. k. Gesndhtsmte., Berl., vol. 28, 1908, p. 145.
RÉSUMÉ.
Rats are notoriously resistant to bacterial infection. Even plague
usually fails markedly to diminish their prevalence. An epizootic of
bacterial nature, therefore, can not be classed with the natural
enemies of the rat. We are not surprised, then, to learn that the
bacterial viruses have signally failed to accomplish their mission.
These bacterial viruses belong to the colon-typhoid group of
organisms. They are either identical with or closely related to the
original bacillus of mouse typhoid discovered by Loeffler, or the
para-typhoid bacillus type B, which is frequently the cause of meat
poisoning, or the _Bacillus enteritidis_ of Gærtner, which has been
associated with gastro-intestinal disorders.
The claim that these rat viruses are harmless to man needs revision,
in view of the instances of sickness and death reported by various
observers. The pathogenicity for man depends upon the virulence of the
culture, the amount ingested, the nature of the medium in which it
grows, and many other factors.
Danysz virus is pathogenic for rats under laboratory conditions, but
has feeble powers of propagating itself from rat to rat. It rapidly
loses its virulence, especially when exposed to light and air. The
result depends largely upon the amount ingested. The other viruses
have proven even less satisfactory.
Under natural conditions these rat viruses may be likened to a
chemical poison, with the great disadvantage that they rapidly lose
their virulence and are comparatively expensive. They also have the
further disadvantage that chemical poisons do not possess of rendering
animals immune by the ingestion of amounts that are insufficient to
kill or by the ingestion of cultures that have lost their virulence.
PLAGUE ERADICATION IN CITIES BY SECTIONAL EXTERMINATION OF RATS AND
GENERAL RAT PROOFING.
By VICTOR G. HEISER,
_Passed assistant surgeon, U. S. Public Health and Marine-Hospital
Service, chief quarantine officer and director of health for the
Philippine Islands_.
The health officials of the city of Manila, P. I., for the five-year
period from 1900 to 1905 made most valiant efforts to destroy the rats
of the city; approximately $15,000 were paid in rat bounties and
$325,000 in salaries and wages and other expenses for rat catching,
but at the end of that time the rats were apparently as plentiful as
before and the plague was still present. The experience in Tokio and
Osaka had been practically the same. Professor Kitasato expressed the
opinion that a given city could only have up to a certain number
anyhow, because further increase was limited by the amount of
available food, and when the limit had been reached the rats commenced
to eat one another, which prevented more than a certain number ever
being present, and that the increase by breeding was about as rapid as
any method of destruction which had yet been tried.
The following plan was then tried, and the plague among human beings
soon disappeared, there being no cases since April, 1906; and it has
been eradicated among rats each time that it has made its appearance.
A list of the places at which plague-infected rats were found was
made. Each was regarded as a center of infection. Radiating lines,
usually five in number, were prolonged from this center, evenly spaced
like the spokes of a wheel. Rats were caught along these lines and
examined. Plague rats were seldom found more than a few blocks away.
The furthermost points at which infected rats were found were then
connected with a line, as is roughly shown in the diagram on page 206
(Fig. 59.)
The space inclosed by the dotted line was regarded as the section of
infection. The entire rat-catching force, which had heretofore been
employed throughout the city, was then concentrated along the border
of the infected section; that is, along the dotted line. They then
commenced to move toward the center, catching the rats as they closed
in. Behind them thorough rat proofing was carried out. One section
after another was treated in this way until they had all been wiped
out. Once weekly thereafter rats were caught in the previously
infected sections and at other places which were insanitary and which
had been infected in years gone by. This was continued for one year.
The city was then divided as is shown in the diagram facing this page,
and rats are caught once weekly at each point at which the lines
intersect and sent to the laboratory for examination.
[Illustration:
FIG. 59.—Isolated plague-infested center, Manila, P. I.
]
In addition, sanitary inspectors are instructed to bring in dead rats
which have evidently died of disease, and more detailed rat catchings
are made along the water front.
It is understood of course that rat proofing of the entire city should
be thoroughly carried out and constantly maintained.
CONCLUSIONS.
1. Since the above system was adopted plague has disappeared in the
city of Manila; among human beings in 1906; among rats in 1907, and it
has not reappeared since.
2. That the cost is only a small fraction of that of general rat
extermination.
3. That the plan is thoroughly practical for any kind of a city.
[Illustration:
FIG. 60.—General Scheme for testing plague rat infection, City of Manila.
Sanitary Map Bureau of Health. _Escala 1:38,500_
]
THE RAT IN RELATION TO SHIPPING.
By WILLIAM C. HOBDY,
_Passed Assistant Surgeon, Public Health and Marine-Hospital Service_.
Since men first went down to the sea in ships the rat’s voyage-making
tendencies have been known, and their fecundity is as well established
as their fondness for travel. The record does not state that there
were more than a pair on the ark at the beginning of her voyage, but
the chances are better than even that her skipper began that voyage
with more rats than his manifest showed; but whether he did or not, we
can be sure he had more at the end of the voyage than at the
beginning. Whether or not succeeding generations inherited from their
forbears on the ark this well-known wanderlust is undetermined, but it
is a fact that the intimacy and companionship established and begun
then have been persistently maintained by the rat ever since. His
travels have been coextensive with man’s, until to-day there is not a
port on earth where the rat is not present. Any exception to this
statement simply proves the rule. The rat is cute; he knows when he is
well off and his absence from a port does not prove that he has not
been there, but that he has been too intelligent to follow man ashore.
In establishing this shipboard intimacy there has been no “by your
leave” courtesy on his part either; he goes without consent—against
orders, even—and man’s ingenuity has as yet discovered no effective
means of keeping him off. This is not surprising when the rat’s
ability as a rope walker is considered. I have seen a rat gallop with
all appearance of enjoyment along an inclined electric cable from a
church steeple on one side of a street into the second story of a
hotel on the other. Others have been seen traveling along the
telephone wires from house to house, and on shipboard they frequently
have runways on small pipes along which they scurry in perfect
security. When a ship is fended off 6 feet from the dock and her gang
plank is lifted or guarded she is still freely accessible, because all
her mooring lines are only so many highways along which rats can and
do pass with ease and in perfect safety.
This fondness for ships and sea travel is shared by the various
species of the rat family, but the _Mus norvegicus_ has earned the
reputation of being the greatest traveler of them all. He almost
invariably predominated among those killed by fumigation on shipboard.
That he finds life on shipboard easy and the conditions satisfactory
is proved by the numbers that are destroyed from time to time by
fumigation. While in charge of the outgoing quarantine work in San
Francisco the chief engineer of a small lumber carrier called to book
his vessel for fumigation. The vessel was small, only 260 tons, and
carried nothing but lumber and her own ship’s stores, but the chief
declared she was overrun with rats, and to prove it showed where they
had eaten the patches from his shoes. He declared they robbed him of
his sandwich when he came off watch, and requested me to give her a
thorough fumigation. This was done. The next morning the agent of the
vessel phoned to ask how I measured rats, stating that on this vessel
they had collected “a barrelful and seven.” Three hundred and ten on a
little vessel of only 260 tons burthen.
On another vessel after one fumigation 100 were collected immediately
after fumigation, but a few days later, when the vessel was undergoing
extensive repairs, 425 others were found—a total of 525 on one small
vessel. These numbers are small, however, when compared with the
results obtained on others, i. e., on grain-carrying vessels. For
instance, a vessel was fumigated some years since in Bombay where
1,300 were destroyed at one time, and the _Minnehaha_, a new vessel
only nine months in commission, on fumigation in London, England, in
May, 1901, yielded a bag of 1,700 rats.
ADAPTABILITY OF THE RAT TO HIS SURROUNDINGS.
In addition to his qualities as a sailor and tight-rope walker, the
rat has the power of adapting himself to most unusual conditions and
surroundings. At the beginning of the outgoing work in San Francisco
it was urged that rats either could not or would not live on any part
of tank ships engaged exclusively in carrying oil, owing to the fumes
and vapors that permeated the entire vessel. This statement was
unquestionably correct for those compartments in which the oil itself
was stored or carried. It was not true, however, for the
superstructure of these vessels, for on one of the oil carriers 60
rats were found after one fumigation, and of the thirty or more
vessels of this class that were regularly fumigated in San Francisco,
although the odors of oil or gasoline were quite strong in the living
compartments, not one was found that did not harbor rats. Still more
remarkable, as illustrating the rat’s adaptability, was the fact that
from the large refrigerating plants which some vessels carried and in
which fumigation had not been practiced for a long time rats were
obtained that had grown a fur an inch and a half long to protect
themselves from the cold.
DAMAGE TO CARGO.
That rats on shipboard in any such numbers as mentioned above must do
much damage to cargo can not be doubted.
Inquiry as to the extent of this damage showed that there were no data
on the subject. That such damage was common and considerable, however,
was revealed by the fact, elicited by these inquiries, that nearly
every steamship company on both the Atlantic and Pacific took
precautions both to keep rats from getting on board and to destroy
them after they did. One example will show what damage may occur. The
British steamer _Gadsby_, on a voyage from India to Antwerp, covering
a period of twenty-nine days, had 44,000 out of 46,000 bags of wheat
cut by rats, with an estimated damage of $2,200.
The constant and almost universal presence, then, of rats on shipboard
can not be doubted, and if it could the results of fumigation,
wherever practiced with SO_{2}, would serve to settle the question,
for they are found under all conditions, even on the most unlikely
vessels.
How do these rodents gain access to a vessel? It has been the custom
to assume that they came on board from the docks over the side when
this was possible, and when it was not, as when the vessel was fended
off or stood too high out of the water, that they made use of the
gangways, mooring lines, hawsers, etc., as avenues of communication.
It is still the practice, therefore, in enforcing antirat precautions,
to compel the ship to fend off 6 feet from the dock, to wear fat
funnels on all lines, and to raise the gangway from the dock at night.
Just a word as to these precautions. The most practical fender is a
floating one made of heavy timbers either bolted together into a solid
frame, with the necessary cross braces bolted in, or made up of logs
or spars chained together. They should be long enough to distribute
the pressure of the vessel as the tide moves over a number of piers or
piles so that the weight does not bear, through the medium of these
fenders, on just one or two of the wharf foundations. Such a fender
will stay in position, will do no damage to the vessel, and no matter
how great the amplitude of the tide may be, will always remain below
the ship’s gunwale and can not therefore be utilized by rats as a
means to get on board. Large vessels require at least two. Small ones
need but one, and it was found in San Francisco, in the case of those
vessels changing their mooring several times daily, that this one
could be carried from wharf to wharf by the vessel without trouble or
delay simply by lashing it edgewise outside on top of the guard.
Funnels should be of heavy galvanized iron, circular in shape, and not
less than 36 inches in diameter. The spout of the funnel should be 3
inches in diameter and should be at least 18 inches long. The flange
of the funnel should be soldered to this 18-inch pipe at its middle so
that the spout projects 9 inches out of the funnel and 9 inches into
it. When the two halves of the funnel are brought together this spout
or tube is occupied by the line or hawser to be protected, and by
lashing this tube to the hawser the funnel is held in position and
prevented from lying down. Such a funnel should be put on every line
from the vessel to the dock, and when the tube does not fit the line
the latter should be parceled before the tube is lashed to it.
These, together with raising the gang plank from the dock at night,
make up the precautions ordinarily taken to prevent the rats from
getting on ships. As stated above, they are based on the assumption
that these are the common avenues of entrance. That these precautions
do much good can not be doubted, but in the writer’s opinion they do
not entirely cover the case, for there remains one other road of
ingress, one of the important, if not the most important, which these
precautions do not and can not block and through which rats constantly
get on board, and that is through the medium of the cargo itself.
There is at present nothing to prevent access in this manner to a
vessel and the route is so easy that there can be no doubt that whole
families of rats are carried on board in this way. In fact some
articles of cargo offer inviting harbors and homes to rats,
particularly when these articles have been stored for a time in
rat-infested warehouses. Among such articles of cargo may be mentioned
crockery or china packed in hay or straw or excelsior and loosely
crated; various articles of furniture packed in excelsior, wrapped in
gunny, and loosely crated; wheat, corn, oats, peanuts, or barley when
shipped in bags; and matting in hollow rolls when sewed up in gunny.
Any of these articles could easily become the home of even an entire
rat family after having been stored for a time prior to shipment in a
rat-infested warehouse. As a matter of fact, the last plague rat
discovered in San Francisco was found in a bag of peanuts on the third
floor of a warehouse.
That rats are thus carried on board is absolutely certain in my
opinion. In the recent antiplague campaign at San Francisco there were
ample opportunities for observations along this line, and in no other
way can the presence of rats in troublesome numbers on board certain
vessels be explained. These vessels were new, were freed from rats by
careful and repeated fumigation, and between these acts touched at no
wharves save in Honolulu and San Francisco, where constant antirat
precautions were observed. And yet on their second trip (about five
months after the fumigation had been discontinued) they were badly
rat-infested. Of course, by no means had all these rats been carried
on board in cargo, but the original patriarchs of the colony had,
after which, as is probably the case in all rat-infested ships, their
natural prolific characteristics did the rest.
In the same way, too, rats are carried from ship to shore and the
truth of Kitasatso’s aphorism that “wherever ships go, plague will
go,” at once becomes apparent, and any regulations to prevent the
introduction of such vermin and the plague which they may carry to be
effective must include the inspection of cargo to insure its freedom
from rats, this inspection to be made just before it goes on board.
The relation these rodents bear to plague and the part they play in
its transmission have been thoroughly discussed and set forth in
another article in this work. The work of Ashburton Thompson in
Australia and of the British Medical Commission in India was a
scientific demonstration that plague was primarily a rat disease
transmitted by fleas, while McCoy in the United States has gone
further probably than anyone else in demonstrating the manner in which
the flea does this work. The importance of this relation is emphasized
and the difficulty of ridding a port of pest infection is explained by
a fact, first observed so far as I know by Klein, of London, that rats
suffer from a chronic form of pest, not fatal, at least for a long
time, and during the course of which the rat may exhibit practically
his normal activity. This fact then, that plague is primarily a rat
disease and that it may occur in the rat in a chronic form, shows how
great the danger may be from their presence on shipboard, explains why
it is that where ships go plague will go, and emphasizes the
importance of destroying them on shipboard apart from the damage and
loss which their presence entails.
So important is this and so preeminent is the rôle played by the rat
in plague transmission and propagation that I believe regulations
should demand that all ships be disinfected at least three times, and
better still, four times, a year, for the destruction of rats. If this
precaution were taken, and if to it were added an inspection of cargo
at the port of embarkation to insure its freedom from rats, I believe
the disinfection of cargo could be entirely dispensed with. It is
infectious only in so far as it harbors rats, and if these are not
present disinfection, in my opinion, does as little good in preventing
plague as dipping ballast did in preventing yellow fever.
FUMIGATION.
Once the rat has gained access to a vessel, what is the best method of
getting rid of him?
There are several methods, all of which are effective if properly
used, and all of which depend on sulphur dioxide as the destructive
agent. The following are mentioned: Pot and pan, sulphur furnace,
Clayton system, and Marot system. A choice of one of these methods
will be determined by the cost, the rapidity of fumigation desired,
and the condition of the vessel, whether empty or loaded. No matter
which method is selected, to be effective the sulphur dioxide must be
simultaneously delivered to or generated in every compartment on the
vessel.
For an empty vessel nothing is so satisfactory as the pot and pan
method of generating the gas. It has the following advantages; is more
rapid than any other, is cheaper, is more effective, and is equally
applicable to the largest and the smallest vessel afloat. With a
sufficient number of pots and pans 3,500 pounds of sulphur can be
burned just as quickly as 100. Ten pounds of sulphur in each of 350
pots will be consumed just as quickly as will 10 pounds in any one of
that number, namely, in less than five hours, a fact which was
demonstrated over and over in the outgoing work in San Francisco.
At the beginning of this work it was thought a 2½ per cent gas with
three hours’ exposure would be sufficient. Practice proved, however,
that this was not effective and the strength of gas was increased to 3
per cent and the exposure to five hours which a test, extending over
twelve months and embracing over 3,000 vessels, proved to be ample.
The best pot in which to burn sulphur is 6 inches deep, has a flare of
6 inches—that is, the diameter at the top exceeds the diameter at the
bottom by that much, is from 16 inches to 24 inches in diameter at the
top and has four hemispherical legs about the size of half a billiard
ball. These pots when in use are set in a galvanized iron tub. These
tubs contain a little water, and are of a diameter 6 inches greater
than the top of the pot. The hemispherical legs of these pots will not
punch holes into the tub. The pots are filled with sulphur, which is
hollowed out into a little crater at the top, into which crater from 4
to 6 ounces of alcohol are poured and when all are ready a lighted
match is dropped into each little crater and the compartment is
closed.
In actual practice it was found that an exposure of five hours to a 3
per cent gas would not destroy all the rats in absolutely every case.
Some ships afford better hiding places than others, and on these an
occasional rat would escape. It was the custom, however, to fumigate
all vessels every thirty days and after the third fumigation, on
vessels that did not carry general cargo, no more rats were obtained,
though the fumigations were continued for a number of months.
On those vessels that carried miscellaneous general cargoes a few rats
were found after almost every fumigation. These vessels touched no
wharf from the time they left San Francisco until their return, except
for a short time in Honolulu, where adequate precautions were
observed, and it is difficult to understand how these rats got on
board if they were not carried on in cargo.
For vessels with cargo in their holds the pot and pan method is
dangerous owing to the possibility of fire. For these vessels one of
the other methods of generating the sulphur gas must be used. This
involves the use of an expensive plant consisting of a furnace,
cooling chamber, blower, or fan, and a system of mains and delivery
pipes by means of which the gas is delivered to the various holds and
compartments of the vessel. To be at all effective the gas must be 4½
per cent strength, with at least twenty-four hours exposure. The one
recommendation of such a system is its freedom from danger by fire. It
is too slow; the pipes, even where 6 inches in diameter, are liable to
clogging with sublimed sulphur, an inevitable result if the fans are
driven too rapidly, and it is not possible to do more than one or at
most two ships at a time. The inadequacy of such a method when
compared to the work done in San Francisco where we averaged over nine
vessels every day for almost fourteen months is at once apparent. Many
ships now carry their own disinfecting plants, by means of which not
only is sulphur dioxide generated and pumped into a compartment, but
at the same time also the air of this space is sucked out. This
principle is excellent, but in its application the machines used are
wholly inadequate, having a very limited sulphur capacity per hour and
equipped with delivery pipes in many instances only 2 or 3 inches in
diameter. It would be a matter of days to disinfect some of these
ships with the machines they carry. In San Francisco we again and
again used pots and pans to fumigate these vessels, including the very
compartments in which their own machines sat doing nothing.
The Marot system of generating the gas from compressed liquid sulphur
dioxide has in this country been found too expensive to apply to
vessels. Probably no system will effectually destroy all the rats on a
cargo-laden vessel.
SUMMARY.
To summarize then:
1. The rat is found on all vessels, sometimes in enormous numbers, and
is able to adapt himself to all sorts of conditions. He either gets on
board himself or is carried on in cargo. Owing to his seagoing
tendency, his distribution is world-wide.
2. On shipboard, to live he must do damage to either cargo or stores,
or both.
3. Plague is primarily a rat disease; it may exist in the rat in a
chronic form. Hence where ships go plague will go sooner or later.
4. To prevent the ingress of rats and the consequent spread of plague,
ships should observe antirat precautions, and cargo inspection should
be included in these.
5. At stated intervals, three or, better still, four times a year, all
vessels should be fumigated for the destruction of rats.
6. On empty vessels this can best be done by generating sulphur by the
pot and pan method.
7. On laden vessels some special apparatus must be used to generate
the gas. A longer exposure is required, at least twenty-four hours,
and the gas should be 4½ per cent strength instead of 3 percent. It is
extremely difficult by any method to kill all the rats on a
cargo-laden vessel.
THE RAT AS AN ECONOMIC FACTOR.
By DAVID E. LANTZ,
_Assistant Biologist, United States Department of Agriculture_.
INTRODUCTION.
The world has rightly learned to dread rats as disseminators of
disease, and recent efforts to rid cities of the pests have resulted
chiefly from sanitary considerations. Yet the material losses due to
depredations of rats are now, and always have been, a sufficient
argument for their destruction. The requirements of sanitation and
public health are slowly bringing to pass what economic interests
failed to accomplish, namely, a general recognition of the fact that
the rat is a standing menace to prosperity. To point out some of the
many ways in which rats inflict injury and the extent to which they
drain the resources of the people is the object of the present
chapter.
UTILITY OF THE RAT.
Do rats serve any useful purpose? With very slight reservation, the
question may be answered in the negative. There have been times and
places in which the rat’s work as a scavenger accomplished good, but
modern methods of garbage disposal are superseding the feeding it to
rats.
It was Robert Southey, the poet, who, nearly a century ago, humorously
suggested as the first three steps to eradicate rats—first,
introducing them as a table delicacy; second, utilizing the skins; and
third, inoculating them with a contagious disease.[BY] The last of
these plans is now receiving considerable attention from
bacteriologists, but the others, for obvious reasons, have been
neglected.
Footnote BY:
Omniana, vol. 1, p. 25, 1812.
It is true that under exceptional circumstances the rat has been a
source of human food. The principal instances on record were during
the siege of Paris in 1870, and during the siege of the French
garrison at Malta, 1798–1800, when food was so scarce that rat
carcasses brought high prices. Another was on board the ship _Advance_
during an arctic winter, when Doctor Kane attributed his entire
immunity from scurvy to his diet of fresh rats, of which none of the
other members of the party would partake.[BZ]
Footnote BZ:
Second Grinnell Expedition, vol. 1, p. 393, 1856.
The statement is often made in newspapers, and even in encyclopedias,
that in Europe, and especially in France, rat skins are extensively
used in the manufacture of gloves. The late Frank T. Buckland, about a
half century ago, made diligent inquiry in London, and through friends
in Paris and other places on the Continent, but found no confirmation
of such statement. He concluded that either rat skins were not used
for making gloves or the manufacturers were unwilling to acknowledge
such a use.[CA] Personally, the writer has been unable to learn of any
demand or market for rat skins at the present time. They are not
strong, and the fur is of inferior quality. The occasional finding of
one or more rat skins in the fur lining of coats is probably to be
explained by the fact that they are sometimes included in lots of
small muskrat skins (“kitts”) and overlooked by the buyer.
Footnote CA:
Curiosities of Natural History, first series, p. 83, 1857 (Reprint
1900).
DESTRUCTIVENESS OF THE RAT.
Rats inflict injury in a surprising number of ways, and before an
attempt is made to consider the magnitude of the losses due to these
animals a statement of the nature of their depredations should be
made.
DAMAGE TO GRAINS.
Cultivated grains are the favorite food of rats. The animals begin
their depredations by digging up the newly-sown seed. They eat the
tender sprouts when they first appear, and continue destroying the
plants until the crop matures. They then attack the grain itself, and
after harvest take toll from shock, stack, mow, crib, granary,
elevator, mill, and warehouse. When rats are abundant their
depredations amount to an appreciable percentage of the entire yield
of grain, and in exceptional cases whole crops have been ruined.
INDIAN CORN.
Probably this crop suffers greater injury from rats than any other in
the United States. To some extent the animals dig up newly planted
corn, but their injury to the maturing grain is far greater. They are
especially fond of corn in the milk stage, and often climb the upright
stalks and strip the cobs bare. In this way sometimes whole fields are
destroyed.
Corn in the shock is often attacked by rats, especially in parts of
fields adjacent to hedges, drains, or embankments that afford shelter
for the animals. A pair of rats often make a corn shock their home,
and soon destroy both grain and fodder.
Corn in cribs is often damaged by rats. Many cribs are built close to
the ground, and rats take up their abode under the floor. They soon
gnaw through the wooden barrier and have free access to the grain.
They shell the corn and eat the soft part of the kernels, wasting much
more than they eat. They carry the grain into underground burrows and
bring up moist soil from below, which in contact with the grain makes
it moldy and unfit for market or for feeding to stock. A number of
farmers have reported the loss by rat depredations of from a fifth to
a half of the contents of a large corn crib during a single winter.
An Iowa farmer, writing to an agricultural journal, relates the
following experience:
We had about 2,000 bushels of corn in three cribs to which rats ran,
and they ate and destroyed about one-fourth of the corn. Much of it
was too dirty to put through the grinder until it had been cleaned
an ear at a time. All the time we were poisoning and trapping the
rats. We killed as high as 300 rats in two days and could hardly
miss them. They destroyed more than enough corn to pay taxes on 400
acres of land.[CB]
Footnote CB:
Missouri Valley Farmer, April, 1907.
Throughout the United States, but especially in the West and South,
corn is often stored for months in rail or other open pens, to which
rats have free access. Often the loss in a single season would pay for
the construction of rat-proof cribs, or at least for wire netting,
that would fully protect the crop.
SMALL GRAINS.
Much has been written about the rat as a house and barn pest, but its
depredations in the fields have usually been overlooked. In some
localities the common rat, as well as the house mouse, swarms in the
fields, especially in summer, and subsists entirely upon the farmers’
crops.
Stacked grain is peculiarly exposed to rat depredations. In the United
States, although the cost of protection is small, rats are seldom
fenced away from stacks, and, if threshing is delayed, serious loss
results. Often, at the removal of a stack, large numbers of rats are
discovered, which have been living at the expense of the farmer. As
early as 1832 a farmer in Frederick County, Md., with the help of men
and dogs, killed 217 large brown rats from one stack of rye.[CC] In
England instances are on record of the killing of over a thousand rats
from one stack of wheat.
Footnote CC:
Am. Turf. Register, vol. 3, p. 632, August, 1832.
The destruction of feed by rats is a serious loss not only on the farm
but also in city and village. The feed bin or barrel is often left
uncovered and rats swarm to the banquet thus exposed. Small feeders
suffer greater proportional losses, for managers of larger barns
recognize the enormous drain and usually provide rat-proof bins, if
not rat-proof stables. When rats have access to a stable they take a
good share of the feed directly from the mangers, but the loss is
seldom noticed.
Rats are exceedingly fond of malt, and in malt houses and breweries
constant watchfulness is needed to prevent losses. Mills, elevators,
and warehouses in which grain and feed stuffs are stored are subject
to constant invasion by rats and mice.
A full-grown rat consumes about 2 ounces of grain daily. A half-grown
rat eats nearly as much as an adult. Fed on grain, therefore, a rat
eats from 45 to 50 pounds a year. The cost depends somewhat on the
kind of grain. If wheat, the value is 60 to 75 cents; if oatmeal,
about $1.80 to $2. Several feeders of horses in Washington, D. C.,
estimated the cost of keeping each rat on their premises at $1 a year.
Even though half the grain eaten is waste, the direct loss from this
source to feeders is enormous.
MERCHANDISE IN STORES AND WAREHOUSES.
The loss from depredations of rats on miscellaneous merchandise in
stores, markets, and warehouses, is second only to the losses on
grains. Not only are food materials of every kind subject to attack,
but the destruction of dry goods, clothing, books, leather goods, and
so on is equally serious. Merchandise other than foodstuffs is usually
destroyed for making nests, but books and pamphlets, especially the
newly bound, and some other articles, furnish food in the glue, paste,
oils, or paraffin used in their manufacture. Some kinds of leather
have a peculiar attraction for rats, while others are never touched.
Shoes are seldom gnawed unless they have cloth uppers or are made of
kid. New harnesses are not often attacked, except collars, which
contain straw, and cruppers, which are stuffed with flaxseed. Old
harness leather is salty from the perspiration of horses, and rats and
mice gnaw it for this reason. Kid gloves and other articles made of
similar leather are often destroyed by rats.
Lace curtains, silk handkerchiefs, linens, carpets, mattings, and
other dry goods in stores are often attacked by rats. Some of the
stuffs contain starch, which serves as food, but most of them furnish
nesting materials only. A slight injury makes these articles
unsalable; this is especially true of white goods, which are easily
ruined by soiling. Nearly all large dry goods and department stores
suffer heavy losses from rats. Grocers, druggists, confectioners, and
other merchants also have similar experiences, and to the direct
losses must be added the sums expended in fighting the pests.
MERCHANDISE IN TRANSIT.
Merchandise billed for shipment often lies for days in stations and
warehouses or on wharves, where depredations of rats and mice cause
heavy losses to shippers and consignees. Similar losses occur on boats
carrying merchandise from port to port.
Fruits and vegetables in transit on steamboats are often destroyed or
damaged by rats. Tomatoes, cucumbers, sweet potatoes, bananas,
oranges, grape fruit, peanuts, and similar produce shipped by water
from the South, especially in winter, reach northern markets with a
large percentage of loss.
In view of the practicability of destroying rats on ships by
fumigation, and the ease with which rat-proof compartments for stowing
produce can be constructed, it would seem that losses of this nature
should be entirely prevented.
POULTRY AND EGGS.
Aside from disease, the greatest enemy of poultry is the rat. The loss
from rats varies with their abundance and the care taken to exclude
them from the poultry yard. The magnitude of the damage is not
generally known, because much of it is blamed on other animals,
particularly minks, skunks, and weasels. Much of the injury occurs at
night, and the actual culprit is seldom detected. Farmers have heard
that minks, skunks, and weasels prey upon poultry. What more natural
than to conclude that one of these animals is doing the mischief,
especially if one has been seen about the premises?
Rats often prey upon small chicks, capturing them in the nests at
night or even about the coops in the daytime. The writer has known
rats to take nearly all the chicks on a large poultry ranch, and over
a large section of country to destroy nearly half of a season’s
hatching. Young ducks, turkeys, and pigeons are equally liable to
attack, and when rats are numerous, are safe only in rat-proof yards.
A writer in a western agricultural journal states that in 1904 rats
robbed him of an entire summer’s hatching of three or four hundred
chicks.[CD] A correspondent of another newspaper says, “Rats destroyed
enough grain and poultry on this place in one season to pay our taxes
for three years.”[CE] When it is remembered that the poultry and eggs
marketed each year in the United States have a farm value of over
$600,000,000, it will be seen that a small percentage of loss
represents an enormous sum.
Footnote CD:
Homemaker (Des Moines, Iowa), May 27, 1907.
Footnote CE:
Missouri Valley Farmer, April, 1907.
The destruction of eggs by rats is great, not only on the farms where
they are produced, but also in the markets. Commission men and grocers
complain of depredations upon packed eggs. The animals break and eat a
few eggs at the top of a case and the broken yolks run down and soil
the eggs below. Then, too, rats carry away unbroken eggs, displaying
much ingenuity in getting them over obstacles, as up or down a
stairway.
A commission merchant in Washington, D. C., states that he once stored
100 dozen eggs in a wooden tub in his warehouse and left them for
nearly two weeks. He then found that rats had gnawed a hole through
the tub, just under the cover, and had carried away 71½ dozen, leaving
neither pieces of shell nor stains to show that any had been broken.
Besides their destruction of eggs and young fowls, rats eat much of
the food put out for poultry. They are destructive also to tame
pigeons and their eggs, but particularly to young squabs. They climb
the wire netting and gain entrance to the cages through the same
openings by which the pigeons come and go. Fanciers are often put to
great trouble to protect their pigeons from rats, and because of these
pests some of them have abandoned the business.
GAME AND WILD BIRDS.
The rat is the most serious pest in European game preserves. A writer
in Chambers’s Journal says:
In a closely preserved country at the end of an average year the
game suffers more from the outlying rats of the lordship than from
the foxes and mustelines together. The solitary rats, whether males
or females, are the curse of a game country. They are most difficult
to detect, for in a majority of cases their special work is supposed
to be done by hedgehog, weasels, or stoat.[CF]
Footnote CF:
Chambers’s Journal, vol. 82, p. 64, January, 1905.
The propagation of game birds is becoming a promising industry in the
United States. The difficulties of the business are not yet fully
known, but the rat is an enemy with which the raiser of game will have
to contend. The animal has already proved itself a foe in American
pheasantries.
Our wild native game birds are less subject to rat depredations than
birds kept in confinement. The nests of ruffed grouse are in
woodlands; those of the prairie hen and related species are on plains
remote from the haunts of rats. The quail, however, often makes its
nest within the summer range of rats, which destroy many of its eggs.
Rats are said often to destroy the nests of wild ducks, woodcock, and
other marsh birds. Terns have been entirely driven from their nesting
grounds in this way. In England the common tern was extirpated from
the Thames marshes; and on Loggerhead Key, Tortugas Islands, off the
Florida coast, rats recently nearly exterminated a colony of least
terns by destroying the eggs.
The nests of many ground-nesting and other song birds are robbed by
rats. Crows, jays, snakes, and skunks are blamed for most of the
destruction and the actual offender seldom suspected. While the other
animals named do part of the mischief, the rat is a more serious foe
of song and game birds than any of these.
FRUITS AND VEGETABLES.
A well-known form of damage by rats is the destruction of fruits and
vegetables in cellars and pits. Apparently no garden vegetable or
common fruit is exempt from attack. But the rat does not confine its
depredations to stored fruits and vegetables. It attacks ripe
tomatoes, melons, cantaloupes, squashes, pumpkins, sweet corn, and
many other vegetables in the field; and often the depredations are
attributed to rabbits or other animals, which may or may not be
concerned in the mischief.
Rats are fond of the small fruits, eating not only the fallen but
climbing vines and canes to obtain the ripe grapes or berries. They
eat also apples, pears, cherries, and other fruits. The brown rat,
while not so expert as the black or the roof rat, readily climbs trees
and obtains fruit even at the extremities of the branches.
Among tropical fruits injured by rats are oranges, bananas, figs,
dates, cocoanuts, and especially the pods of cacao (_Theobroma
cacao_), from which chocolate is manufactured. H. N. Riddey, writing
of his experiences on the island of Fernando do Noronha, South
America, mentions the destructiveness of rats in this penal colony.
They climb the cocoanut palms and papaw trees to devour the fruit, and
do mischief in melon patches. To lessen the evil, each convict was
required to bring in a certain number of dead rats, and battues were
held monthly to satisfy the requirement. Sometimes the number killed
in a single hunt reached 20,000.[CG]
Footnote CG:
Zoologist, vol. 46, p. 46, 1888.
Fruits and vegetables grown under glass are subject to injury by rats.
The animals usually find entrance to greenhouses by way of openings
for pipes or drains.
FLOWERS AND BULBS.
Rats attack seeds, bulbs, and the leaves, stems, and flowers of
growing plants, whether in the greenhouse, propagating pits, or
elsewhere. Of flowering bulbs, the tulip suffers most from rats.
Hyacinths also are eaten; but, probably because they are slightly
poisonous, narcissus and daffodil bulbs escape injury. Rats eat pinks,
carnations, and roses, cutting the stems off clean. They denude
geraniums of both flowers and leaves. They attack the choicest blooms
of chrysanthemums and carnations in markets, stores, and exhibition
rooms, causing heavy losses.
FIRES.
Rats and mice cause many fires. Several specific instances have been
reported by the fire department of the city of Washington within the
past two or three years. It is likely that some of these fires are
caused by rats gnawing matches. The animals are fond of paraffin,
which is often used to protect match heads. They carry the matches to
their nests, which are composed of paper and other combustible
materials, and the conditions for a conflagration are ready. Since the
heads of matches contain from 14 to 17 per cent of phosphorus, actual
gnawing is not required to ignite them, but heat or friction from any
cause may suffice.
Fires in mills or warehouses have sometimes been traced to the
spontaneous ignition of oily or fatty rags and waste carried under
floors by rats. Cotton and woolen mills are said to be peculiarly
subject to fires of this kind.
Sometimes rats cause fires by gnawing through the lead pipes leading
to the gas meter. Workmen or others, searching for the leak,
accidentally ignite the gas. Phillips’s warehouse, London, was twice
badly damaged by fires originating in this way, and in several
instances the sleeping inmates of houses have been in danger of
asphyxiation by gas freed in this manner.
The most common way in which rats and mice cause fires is by the
destruction of the covering of electric light wires under floors or in
partition walls. A considerable percentage of the enormous fire losses
in the United States is caused by defective insulation of wires. After
wires are once in position rats are the chief agents in impairing the
insulation. These animals do much mischief also by gnawing off the
coverings of telephone wires. In the case of electric light wires the
covering is probably used by the rats for nesting material, but
frequently the paraffin in the insulation is the object of attack.
BUILDINGS AND FURNITURE.
Rats seem to be able to gnaw through almost any common material except
stone, hard brick, cement, glass, and iron; neither wood nor mortar
suffice to keep them out of bins or rooms. They sometimes gnaw through
walls or doors in a single night. In the same way they enter chests,
wardrobes, bookcases, closets, barrels, and boxes. Almost every old
dwelling bears evidence of its present or former occupancy by rats.
Often the depreciation of houses and furniture is largely due to marks
left upon them by rats—marks that paint and varnish can not hide.
Damage to dwellings by rats is a large item. The decay of sills and
floors is hastened by contact with moist soil brought up from rat
burrows. Ceilings, wall decorations, and floor coverings are flooded
by leaks in lead pipes or wooden tanks gnawed by rats. Bricked areas
and even foundations are undermined and ruined by rats. All this is
real waste and a constant drain on the resources of the country.
MISCELLANEOUS.
A few instances of miscellaneous damage by rats may be mentioned to
show the great variety of mischief chargeable to the animals.
A Washington, D. C., merchant reported that at one time rats in his
store destroyed 50 dozen brooms worth $2.50 a dozen. In another store,
in a single night, they broke $500 worth of fine chinaware on shelves
and tables. A dealer in harness reported the loss of $400 worth of
collars in one season. The manager of a restaurant complained of an
average loss of $30 a month in table linen ruined by rats and mice. A
hotel reported the destruction of $75 worth of linen in a month.
At Mobile, Ala., in March, 1908, lost jewelry worth $400 was recovered
from a rat’s nest in the home of Señor Viada.
In London rats at one time killed all but 11 out of an aviary of 366
birds.
At Hamburg, Germany, Carl Hagenbeck once had to kill three young
African elephants because rats had gnawed their feet, inflicting
incurable wounds.
Rats often gnaw the hoofs of horses until they bleed. They kill young
lambs and pigs, and have been known to gnaw holes in the bodies of
very fat swine, causing death.
Like the muskrat, the brown rat often burrows into embankments and
dams, causing serious breaks.
The rat is one of the greatest enemies with which the sugar planter
has to contend, destroying acres of growing cane.
In rice plantations rats not only break down and destroy the growing
crops, but burrow into the dikes and flood the fields at the wrong
season.
On the London docks and on shipboard ivory is often badly damaged by
rats. They select for attack the greenest tusks, which are the more
valuable.
Mail sacks and other kinds of bagging are greatly injured by rats. The
consequent loss and necessary outlay for repairs are a large item in
post-office expenditures and in mills and other places where bagging
is used.
About the year 1616 rats caused a two years’ famine in the Bermudas.
In the southern Deccan and Mahratta districts of India rats ate a
large part of the scant crops of 1878 and 1879, and were regarded as
in a great measure responsible for the severe famine which
followed.[CH] A writer in Chambers’s Journal stated that the Dutch
abandoned the Isle of France (Mauritius) in 1610 because of the great
abundance of rats.[CI]
Footnote CH:
Brit. Med. Journ., p. 623, September 15, 1905.
Footnote CI:
Chambers’s Journal, vol. 21, p. 244, 1854.
AMOUNT OF LOSSES CAUSED BY RATS.
The damage done by a single rat varies greatly with the circumstances.
We have already stated that the cost of feeding a rat on grain varies
from 60 cents to $2 a year. Assuming that much of the rat’s food is
waste, each rat on a farm will cause a loss of over 50 cents a year.
In cities the damage by a single rat probably averages more than in
the country. Hotel managers and restaurant keepers state that $5 a
year is a low estimate of the loss inflicted by a rat. In making an
estimate it should be remembered that the rat is to be charged not
only with the food it actually consumes but also with what it destroys
or pollutes and renders unfit for use.
If an accurate census of the rats in the United States were possible,
and if the minimum average loss caused by a rat were known, an
estimate of the total annual losses from their depredations could be
made. It was on such a minimum basis that the Incorporated Society for
the Destruction of Vermin arrived at their total estimate of
£15,000,000 ($73,000,000) as the yearly losses from rats in Great
Britain and Ireland. Three propositions were assumed: first, that in
cities and villages the number of rats equals the population; second,
that in the country there is at least one rat for every acre of
cultivated land; third, that each rat in the kingdom inflicts a damage
of at least a farthing per day. Circulars asking whether these
assumptions are excessive were distributed throughout the country.
From 90 to 99 per cent of the replies fully indorsed each of the
assumptions.
It can readily be seen that the English basis of estimate would not
apply to farm conditions in the United States, where the area in the
twelve leading crops alone is over 250,000,000 acres. On a basis of a
rat per acre and damage of a farthing per day the annual loss on this
area would be $450,000,000, a sum much too great for serious
consideration. However, in the more thickly populated parts of the
country an estimate of one rat per acre would not be excessive; and it
is probable that in most of our cities there are quite as many rats as
people. Yet it would be unsafe, owing to our vast territory and
varying conditions, to make these assumptions the basis for
conclusions.
Over a year ago the writer made an attempt to investigate actual
conditions, and thus arrive at an estimate of the total damage by rats
in the cities of Washington and Baltimore. From the data obtained the
direct annual damage in the two cities was calculated at $400,000 and
$700,000, respectively. The Census Bureau in 1906 estimated the
population of these cities at 308,000 and 554,000, respectively. If
the estimates of damage were correct, the average loss for each person
is $1.27 a year; and, on the same basis, the 28,000,000 of urban
population in the United States (census of 1900) sustains an annual
direct injury of $35,000,000 from rats. This is considerably lower
than on the English assumption, which would make the losses in our
cities over $50,000,000.
Denmark (population 2,500,000) has an estimated rat bill of about
$3,000,000 a year, or $1.20 a person. Germany (population 56,000,000)
is said to sustain a loss from rats of 200,000,000 marks ($47,640,000)
a year, or about 85 cents for each person. The per capita estimate for
the United Kingdom is about double that made for Germany. In France
the loss from rats and mice for a single year (1904) was placed at
$38,500,000, or a little over a dollar for each of its 38,000,000
inhabitants. These estimates are supposed to include only direct
losses, but they vary enough to show that no common basis can be
assumed for all countries. With present information, therefore, any
attempt to state the amount of loss from rats in the United States
would be largely guesswork. Considering the population and wealth of
the country, however, and the vast area over which rats are abundant,
it is not unreasonable to conclude that in the United States the
losses from rats amount to much more than in any of the other
countries named.
INDIRECT LOSSES.
To the direct losses caused by rats must be added the cost of fighting
the animals and of protecting property from them. In our larger cities
a number of so-called expert rat catchers are to be found, who operate
with dogs, ferrets, traps, poisons, or other means, and who have an
extensive clientage among merchants, hotel managers, and others. These
pay the rat catcher a yearly or monthly stipend to keep their premises
free of rats and mice. Some of the large establishments pay $200 to
$600 yearly for such service. While the agreements are seldom kept in
full, the clients are usually satisfied that results warrant the
expense. Even when no contractor is employed, merchants are at expense
for traps, poisons, the keep of cats or dogs, and other means of
fighting rats. The same is true in less degree of nearly every
householder.
The cost of protecting property from rats is no small item. It
increases the expense of nearly all building, but it greatly reduces
direct losses from the animals. The economy of rat-proof construction
is everywhere manifest, in city or country, and the necessity for it
can not be too strongly emphasized.
Depreciation of property and loss of rents and custom are items not
generally thought of in connection with rat damage. A few years ago
the writer knew of almost an entire block of city houses that remained
untenanted for several months, because infested by rats. As the houses
were otherwise desirable, the loss of rent to the owners was probably
nearly $2,000. The presence of rats in markets, hotels, and
restaurants inevitably results in loss of custom, besides the direct
damage by the rodents.
From every point of view the keeping of rats is exceedingly expensive,
and the sooner our population can be made to realize the enormous
drain upon our resources caused by these rodents the sooner can
concerted measures for their destruction be made effective.
THE RAT IN RELATION TO INTERNATIONAL SANITATION.
By Asst. Surg.-Gen., JOHN W. KERR,
_Public Health and Marine-Hospital Service_.
Rats, like man, had their origin in Asia, from which continent they
have finally become disseminated throughout the world. They, too, like
man, are great travelers, and therefore prey on the commerce of the
ships in which they are carried. For this reason, and on account of
the fact that they are subject to plague and may transmit the disease
from one country to another, these animals have an influence on
international policy, and their control aboard ships is an
international problem.
It has been estimated that there are as many rats as there are human
beings, and that each rat causes each day a loss by the destruction of
material of at least half a cent.
Assuming that the rat population aboard ships is as great as the human
population—and my experience gained during the fumigation of ships to
kill rats convinces me that on the whole it is greater—some idea may
be had of the enormous migrations of rats and the toll they exact for
food from international commerce. Some idea can also be had of the
danger of rats in transmitting plague when it is remembered that 51
countries have been infected with the disease since the present
pandemic began in Canton, China, in 1894, and when it is known that at
least 146 ships have had plague infection on board during that time.
During the International Sanitary Conference of Paris in 1903 the
influence of the rat in transmitting plague was borne in mind, and the
international sanitary agreement, which was signed ad referendum
December 3, 1903, requires the destruction of rats aboard
plague-infected ships, recommends it on ships suspected of being
plague infected, and permits it on ships indemne from plague. The ship
is considered indemne from plague which, although coming from an
infected port, has had neither death nor case on board either before
departure, during the voyage, or at the moment of arrival.
The International Sanitary Convention signed at Washington, October
14, 1905, follows the text of the Paris convention, with respect to
plague, consequently embodying similar requirements and
recommendations as follows:
ART. XX. _Classification of ships._—A ship is considered as infected
which has plague, cholera, or yellow fever on board, or which has
presented one or more cases of plague or cholera within seven days,
or a case of yellow fever at any time during the voyage.
A ship is considered as suspected on board of which there have been
a case or cases of plague or cholera at the time of departure or
during the voyage, but no new case within seven days; also such
ships as have lain in such proximity to the infected shore as to
render them liable to the access of mosquitoes.
The ship is considered indemne which, although coming from an
infected port, has had neither death nor case of plague, cholera, or
yellow fever on board, either before departure, during the voyage,
or at the time of arrival, and which in the case of yellow fever has
not lain in such proximity to the shore as to render it liable, in
the opinion of the sanitary authorities, to the access of
mosquitoes.
ART. XXI. Ships infected with plague are to be subjected to the
following regulations:
1. Medical visit (inspection).
2. The sick are to be immediately disembarked and isolated.
3. Other persons should also be disembarked, if possible, and
subjected to an observation,[CJ] which should not exceed five days,
dating from the day of arrival.
Footnote CJ:
The word “observation” signifies isolation of passengers, either
on board ship or at a sanitary station, before being given free
pratique.
4. Soiled linen, personal effects in use, the belongings of crew[CK]
and passengers which, in the opinion of the sanitary authorities are
considered as infected, should be disinfected.
Footnote CK:
The term “crew” is applied to persons who may make, or who have
made, a part of the personnel of the vessel and of the
administration thereof, including stewards, waiters, “cafedji,”
etc. The word is to be construed in this sense wherever employed
in the present convention.
5. The parts of the ship which have been inhabited by those stricken
with plague, and such others as, in the opinion of the sanitary
authorities, are considered as infected, should be disinfected.
6. The destruction of rats on shipboard should be effected before or
after the discharge of cargo, as rapidly as possible, and in all
cases with a maximum delay of forty-eight hours, care being taken to
avoid damage of merchandise, the vessel, and its machinery.
For ships in ballast, this operation should be performed immediately
before taking on cargo.
ART. XXII. Ships suspected of plague are to be subjected to the
measures which are indicated in Nos. 1, 4, and 5 of Article XXI.
Further, the crew and passengers may be subjected to observation,
which should not exceed five days, dating from the arrival of the
ship. During the same time the disembarkment of the crew may be
forbidden, except for reasons of duty.
The destruction of rats on shipboard is recommended. This
destruction is to be effected before or after the discharge of
cargo, as quickly as possible, and in all cases with a maximum delay
of forty-eight hours, taking care to avoid damage to merchandise,
ships, and their machinery.
For ships in ballast this operation should be done, if done at all,
as early as possible, and in all cases before taking on cargo.
ART. XXIII. Ships indemne from plague are to be admitted to free
pratique immediately, whatever may be the nature of their bill of
health.
The only regulation which the sanitary authorities at a port of
arrival may prescribe for them consists of the following measures:
1. Medical visit (inspection).
2. Disinfection of soiled linen, articles of wearing apparel, and
the other personal effects of the crew and passengers, but only in
exceptional cases when the sanitary authorities have special reason
to believe them infected.
3. Without demanding it as a general rule, the sanitary authorities
may subject ships coming from an infected port to a process for the
destruction of the rats on board before or after the discharge of
cargo. This operation should be done as soon as possible, and in all
cases should not last more than twenty-four hours, care being taken
to avoid damaging merchandise, ships, and their machinery, and
without interfering with the passing of passengers and crew between
the ship and the shore. For ships in ballast this procedure, if
practiced, should be put in operation as soon as possible, and in
all cases before taking on cargo.
When a ship coming from an infected port has been subjected to a
process for the destruction of rats, this process should only be
repeated if the ship has touched meanwhile at an infected port, and
has been alongside a quay in such port, or if the presence of sick
or dead rats on board is proven.
The crew and passengers may be subjected to a surveillance, which
should not exceed five days, to be computed from the date when the
ship sailed from the infected port. The landing of the crew may
also, during the same time, be forbidden except for reasons of duty.
Competent authority at the port of arrival may always demand, under
oath, a certificate of the ship’s physician, or in default of a
physician, of the captain, setting forth that there has not been a
case of plague on board since departure, and that no marked
mortality among the rats has been observed.
ART. XXIV. When upon an indemne ship rats have been recognized as
pest stricken as a result of bacteriological examination, or when a
marked mortality has been established among these rodents, the
following measures should be applied:
1. Ships with plague-stricken rats:
(_a_) Medical visit (inspection).
(_b_) Rats should be destroyed before or after the discharge of
cargo, as rapidly as possible, and in all cases with a delay not to
exceed forty-eight hours; the deterioration of merchandise, vessels,
and machinery to be avoided. Upon ships in ballast, this operation
should be performed as soon as possible, and in all cases before
taking on cargo.
(_c_) Such parts of the ship and such articles as the local sanitary
authority regards as infected, shall be disinfected.
(_d_) Passengers and crew may be submitted to observation, the
duration of which should not exceed five days, dating from the day
of arrival, except in special cases, where the sanitary authority
may prolong the observation to a maximum of ten days.
2. Ships where a marked mortality among rats is observed:
(_a_) Medical visit (inspection).
(_b_) An examination of rats, with a view to determining the
existence of plague, should be made as quickly as possible.
(_c_) If the destruction of rats is judged necessary, it shall be
accomplished under the conditions indicated above in the case of
ships with plague-stricken rats.
(_d_) Until all suspicion may be eliminated, the passengers and crew
may be submitted to observation, the duration of which should not
exceed five days, counting from the date of arrival, except in
special cases, when the sanitary authority may prolong the
observation to a maximum of ten days.
ART. XXV. The sanitary authorities of the port must deliver to the
captain, the owner, or his agent, whenever a demand for it is made,
a certificate setting forth that the measures for the destruction of
rats have been efficacious and indicating the reasons why these
measures have been applied.
To be in conformity with these agreements regarding the destruction of
rats, quarantine authorities may demand the fumigation of infected and
suspected ships; suspected ships within the meaning of the treaties
being those on board of which there have been a case or cases of
plague at the time of departure or during the voyage, but no new case
within seven days. In the case of indemne ships, on the other hand,
without demanding it as a general rule, the sanitary authorities may
subject them to fumigation to kill rats. When upon such ships rats
have been recognized as pest stricken, as a result of bacteriological
examination, or when a marked mortality has been established among
these rodents, fumigation is prescribed.
While the classification of ships and the limitations placed on
quarantine procedures in relation thereto, as contained in existing
international sanitary agreements, is more apparent than real, there
appears to be a lack of exactness with respect to the destruction of
rats necessary for the prevention of the importation of plague from
one country to another.
Since the adoption of the international sanitary agreement of Paris in
1903, some of the unproven convictions of that time regarding the rôle
of rats and fleas in the transmission of plague have been proven to be
positive facts. Many epidemiological observations and exact scientific
experiments have demonstrated particularly the importance of the rat
in the propagation of plague and the rôle of the flea as the carrier
of infection from rat to rat and from rats to man.
At the same time there has been a growing conviction that other
agencies, such as passengers, baggage, and merchandise play a very
minor rôle in the dissemination of plague. It is of interest,
therefore, to review the efforts being made at the more important
seaports to exterminate rats, as well as the methods being employed to
that end.
INQUIRY INTO THE CRUSADE AGAINST RATS THROUGHOUT THE WORLD.
The first law in modern times aiming at the destruction of rats
appears to have been enacted in Barbados in 1745.[CL] According to
Boelter this act was incorporated into a new act which was passed in
1748. The same author states that the next legislative body to enact a
law against rats was in Antigua in 1880. In the same article he refers
to the rat ordinance of Hongkong, adopted in 1902.
Footnote CL:
W. R. Boelter, “On Rat Laws,” Journal of Incorporated Society for
the Destruction of Vermin, October, 1908.
Private measures against rats have undoubtedly been practiced from
time immemorial. The action of Denmark, however, in passing a law for
the systematic destruction of rats and providing the organization for
that purpose is perhaps the most notable advance taken on this
subject. A copy of the Danish law appears elsewhere in this
publication.
That the citizens of other countries are equally alive to the
importance of rat extermination is shown by the fact that in England
there exists an incorporated society for the destruction of vermin,
which society in October, 1908, began the publication of a journal
which would supply trustworthy information upon the subject.
It is recognized that a detailed review of past efforts against
rodents would be unprofitable, but on account of the enormous trade
relations between important seaports it is thought that a review of
the measures taken therein against rodents would be of value.
RAT EXTERMINATION IN UNITED STATES PORTS.
Prior to the adoption of the International Sanitary Conventions of
Paris and Washington, the Federal Government had made provision in its
quarantine regulations for the prevention of the spread of plague on
ships through rodents.
The articles contained in the United States Quarantine Regulations,
issued April 1, 1903, and bearing on the subject, are as follows:
14. At ports or places where plague prevails every precaution must
be taken to prevent the vessel becoming infected through the agency
of rats, ants, flies, fleas, or other animals. At such ports or
places the vessel should not lie at a dock, or tie to the shore, or
anchor near any place where such animals may gain access to the
vessel. In case cables are led to the shore they should be freshly
tarred and provided with inverted cones or such other devices as may
prevent rats and other animals passing to the ship. The introduction
of vermin on board the vessel from lighters and all other sources
should be guarded against. In such ports sulphur fumigation should
be resorted to in the holds when empty and from time to time during
loading in order to destroy vermin.
45 (b) Free ventilation and rigorous cleanliness should be
maintained in all portions of the ship during the voyage and
measures taken to destroy rats, mice, fleas, flies, roaches,
mosquitoes, and other vermin.
45 (h) In the case of plague, special measures must be taken to
destroy rats, mice, fleas, flies, ants, and other vermin on board.
128. Vessels infected with plague, or suspected of such infection,
should be anchored at a sufficient distance from the shore or other
vessels to prevent the escape of rats by swimming.
133. Special precautions must be taken against rats, mice, ants,
flies, fleas, and other animals, on account of the danger of the
infection of the disease being spread through their agency.
134. As soon as practicable there shall be a preliminary
disinfection with sulphur dioxide for the purpose of killing rats
and vermin before further disinfecting processes are applied to the
vessel and her cargo. The killing of any escaping rats shall be
provided for by a water guard in small boats, and no person with
abrasions or open sores should be employed in the handling of the
vessel or her cargo.
135. The vessel shall be submitted to a simultaneous disinfection in
all parts with sulphur dioxide to insure the destruction of rats and
vermin. The rats shall be subsequently gathered and burned, due
precautions being taken not to touch them with the bare hands, and
the places where found disinfected with a germicidal solution; and
the quarantine officer shall assure himself that the vessel is free
of rats and vermin before granting free pratique.
Additional regulations prescribe the method of disinfection of vessels
for plague, and elsewhere in this publication is given a detailed
description of the measures taken aboard ships at Angel Island, one of
the national quarantine stations.
Elsewhere is also given an account of the measures taken to eradicate
plague from certain cities on the Pacific coast, among the measures
being the systematic destruction of rodents and practical rat
proofing.
In a letter dated November 21, 1908, requests were made to the
Department of State for reports from certain of the more important
foreign seaports as to systematic measures being practiced for the
destruction of rats. As a result much valuable information has been
received, and acknowledgments are due and here made to the consular
officers furnishing it. The data received was abstracted and
classified according to countries as follows:
RAT EXTERMINATION IN CHINESE CITIES.
Although the present pandemic of plague had its origin in Canton,
China, in 1894, and the disease has been endemic there practically
ever since, Consul-General Bergholz states that the provincial
government of Kwangtung has made no efforts to exterminate rats.
In Amoy the local authorities have never taken measures to encourage
the extermination of rats, and in the absence of assistance from the
local authorities but little can be done toward effective eradication.
An outbreak of plague in Shanghai in December, 1908, was attributed to
the introduction of rats by ships from plague-infected ports.[CM] A
plan of campaign for such an emergency had previously been formulated
and was put in operation. It included collection and laboratory
examinations of rats and organization of rat parties to destroy rats
and render houses rat proof.
Footnote CM:
The Municipal Gazette, Shanghai, January 7, 1909, Health Officer’s
report for December, 1908.
In Tientsin official efforts made to exterminate rats are on lines to
suit the convenience of the particular health official. The consulate
at that port states that generally on the appearance of plague, the
officials pay about one-half cent for each rat brought, and as the
epidemic becomes severe, as much as 2½ cents gold.
In Hongkong, the question of rats in relation to plague has been of
perennial interest. While on duty in the American consulate at that
port, my attention was forcibly called to the influence of rodents in
the transmission of plague. In 1900 it had been the practice to
encourage the destruction of rats in the city, and a reward of 2 cents
Mexican money was offered for each rat brought to the health
department. A certain number of these rats were examined from day to
day from different districts.
In August, 1901, arrangements were made by which the health department
collected and examined a specified number of rats each day to try to
determine in some degree the relative prevalence of plague among these
animals. This practice was continued for several months, with the
result that the mortality among rodents from the disease was shown to
have rapidly decreased until in November practically no
plague-infected rats were found.
In a discussion of the subject, furnished February 2, 1909, by Dr. W.
W. Pierce, medical officer of health, through Consul-General A. P.
Wilder, it is stated that in 1902 the fee for rats was raised to 5
cents, and a special staff of coolies was engaged to destroy rats. The
abuses on account of these bounties were so great, however, that it
was found necessary to discontinue it in 1903, but the method of
trapping rats was continued.
While the total number of rats taken in 1903 was 101,047, Doctor
Pierce stated in effect that on account of the prejudice against
disinfection, it was practically impossible to secure the addresses
where the infected rats were found. The services of the staff were
continued, however, until 1908, when they were abolished because it
was thought, as stated by Doctor Pierce, that results were not
commensurate with the cost, and many complaints were heard. The plan
of furnishing traps to all persons who applied was then introduced,
and in addition, structural methods which had gone on for years were
continued.
The traps were distributed through district committees consisting of
the more educated natives, who were informed that with their
assistance it would be possible to avoid abuses which had been
practiced by the official rat-catching staff.
Doctor Pierce stated that it had been impossible under other systems
to secure the addresses where infected rats were found, and in order
to overcome this prejudice, several hundred receptacles were placed in
different parts of the city whereby the rats could be collected. These
tins were visited from day to day, and by this means it was possible
to locate infected districts.
Doctor Pierce stated that the use of ordinary disinfectants in
plague-infected houses had been discontinued, and that a 2 per cent
mixture in water of a kerosene emulsion made by stirring warm tank
oil, 85 parts added gradually to 15 parts of hot, strong solution of
“sunlight” soap, was used. This solution was found to instantly kill
fleas and bugs, and it has been used systematically.
For ordinary cleansing a 1 per cent solution is used, but Doctor
Pierce stated that on the recurrence of plague special gangs would be
employed to apply a 2 per cent solution in infected localities.
Beginning with January 1, 1909, Doctor Pierce stated that a rat poison
known as “Punjaub rat exterminator” had been laid down, and that the
intensive destruction of rats by this means was under consideration.
In summarizing the measures taken against rats, the American
consul-general stated that four methods were in use, namely, rat
proofing, trapping, poisoning, and use of cats. The use of bacterial
viruses as poisons has thus far been unsatisfactory, and the use of
chemical poisons, such as phosphorus, prepared, and known as “Punjaub
rat exterminator,” has only given moderate results.
The keeping of cats is encouraged, and the consul states that some
hundreds of these animals have been imported from Macao and Canton by
the colony and distributed.
Finally, the consul states that the use of “rat funnels” has long been
compelled whenever large vessels lie at the wharves.
In Sinyang the work of exterminating rats is in charge of a physician
who has 12 assistants, which number, however, may be increased in case
of emergency. The means employed are trapping, offering rewards, and
catching by means of cats. In his report, the consul states that the
best results have been secured by trapping. For ridding houses of
rats, some use is made of fumigation. It is stated that there is not
much danger of rats invading cargo boats, but that in the country rats
are present in enormous numbers, and that the problem of their
destruction has thus far baffled all attempts at solution. Bounties at
the rate of 15 cents per hundred are paid, and in one year the
Government expended for this purpose $32,500.
RAT EXTERMINATION IN MADRAS, BOMBAY, AND CALCUTTA, INDIA.
In Madras, Consul N. B. Stewart states there is no legal enactment in
effect requiring the destruction of rats, but the Government has done
everything in its power to make the public understand the value of
such a measure as a preventive against plague. In 1907 a reward of
one-half anna, equal to 1 cent, was offered by the city for each large
rat killed, and one-fourth anna for each small one. Bounties of
one-fourth anna and one-twelfth anna each for the respective varieties
of rats were still being continued at the time report was made.
In Bombay, where plague has been endemic since 1896, destruction of
rats and examination of all dead rats and evacuation of rat-infected
areas are included among the measures taken by the health department
in connection with plague operations. In his report Consul E. H.
Dennison states that the present antirat campaign in Bombay includes
the distribution of poisons, the trapping of rats, and the reward of 1
cent for each live rat, and a half cent for each dead rat, delivered
to the health department. He also states that there are no by-laws or
acts under which the destruction of rats can be enforced in private
houses.
On account of religious opposition, and to teach the people,
educational posters signed by the health officer were displayed,
containing advice what to do to prevent plague, which in part reads as
follows:
1. Beware of rats in your dwelling houses.
2. To harbor rats is to court plague.
3. Rat infection and consequent rat mortality are the indications of
the impending plague visitation among human beings.
4. Allow the health department staff to place rat traps in and about
your houses to catch rats and take them back.
5. Freedom from plague is in the removal of rats.
6. Inform the health department when dead rats are found in or near
your houses.
7. Clear your houses of all materials likely to harbor rats.
The same placard also contains information regarding disinfection to
kill fleas, evacuation of infected areas, and inoculations to produce
immunity.
In a special report dated January 23 the consul described a new
experiment in rat destruction; that is, an intensive effort in the
Kamatipura district. The district was divided into divisions and
subdivisions in which simultaneously there were distributed for use on
a certain day 19,642 poison baits and 2,670 traps. It was stated that
as a result hundreds of rats were collected the following morning.
No reference is made to measures taken for the destruction of rats
aboard ships in the harbor.
In Calcutta, it is reported by Consul-General W. H. Michael that
various methods are resorted to for the extermination of plague, rats,
the use of poison being the most general. Rewards have been offered
for live and dead rats, and about 11,135 dead rats were produced, but
it was found that a considerable portion of these was picked up by
conservancy coolies, and the reward for dead rats was therefore
discontinued. Of live rats, only 9,447 were produced. After December
1, 1908, the reward was raised to 4 cents, with the result that 49,396
live rats were captured. It is stated, however, that this did not seem
to have any appreciable effect upon the rat population.
RAT EXTERMINATION IN YOKOHAMA AND NAGASAKI, JAPAN.
In the Kanagawa Ken, in which Yokohama is located, the following
ordinances relating to the extermination of rats have been enacted:
_Kanagawa Ken Ordinance No. 64 of 1902 (issued October 8)._
Finders of dead rats within the prefecture shall immediately report
and deliver same to the nearest police, village, or other
authorities in charge. Upon receipt thereof, the police or other
authorities shall without delay transmit the same to the police
headquarters (Yokohama).
_Kanagawa Ken Ordinance No. 45 of 1903 (issued June 26)._
Finders of a dead rat or capturers of a live rat shall report and
deliver the same within twelve hours to the police, mayor, medical
inspector or officer, antiplague committee, or officer in charge of
the Hygiene Guild.
Violation of the foregoing shall be punishable either by a fine or
detention in jail.
_Kanagawa Ken Ordinance No. 63 of 1907 (issued June 8)._
Persons who plan or are engaged in the importation of rats from
without into the city of Yokohama, or persons who plan to breed rats
in the said city, shall be punished by detention in jail or by a
fine.
_Extract from Kanagawa Ken Ordinance No. 14 of 1907, relating to
supervision over storage and warehouses (issued March 6)._
ARTICLE 1. The term “storage and warehouses,” hereinafter mentioned,
shall mean and include any godown, storage or storehouses, or
warehouses, used by storage or warehouse companies, individuals,
forwarding agents or express companies, wholesale dealers, works and
factories, wherein cotton, cereals, or grains, flour, peanuts,
beancake, and other pressed oil cakes, cocoons, feathers, leather,
old or waste cotton, old straw, bags, etc., are stored and kept.
ART. 8, sec. 1. Owners of a storage or warehouse shall exercise at
least four times a year a rigid and thorough method of house
cleaning and rat destruction in the storage or warehouse. The date
and time of cleaning shall be reported to the police, to whose
satisfaction and approval the cleaning must be carried out.
ART. 8, sec. 2. Owners of a storage or warehouse shall furnish and
always keep at each doorway a suitable rat trap, and shall always
endeavor to exterminate rats or pursue such method of extermination
as may be directed by the police.
In forwarding the above ordinances, Vice-Consul Babbit stated that
vessels engaged in foreign trade, when deemed advisable by the harbor
authorities, are required to endeavor to exterminate the rats on board
by sulphur fumigation or other effective methods, as are also
coastwise vessels.
To encourage the extermination of rats, the mayor of Yokohama was
authorized by the city council to pay bounties, the rate being 3 sen
(1½ cents) each. The vice-consul states that in addition to this
purchase price a ticket is given for a lottery, and for each 60,000
rats 156 prizes, amounting to a total of 1,000 yens are given by the
city.
In a table giving the number of rats purchased and sent to the hygiene
bureau for bacteriological examination, it is seen that for the year
ending December 31, 1908, 447,981 were received.
In Nagasaki the municipal council passed an ordinance January 6, 1906,
as follows:
1. Rats to be purchased are of two kinds—house and field rats—and
they must be either caught or found dead within this city.
2. A bounty of 3 sen (1½ cents) shall be paid for each rat with a
ticket, to be cashed on presentation.
3. Such tickets, to be cashed, must be presented at the city office
within thirty days from the date of issue.
4. Rats shall be purchased at the city office, police stations,
branch police stations, police boxes, or by city officials, who go
around for such purpose, by giving a ticket to be cashed upon
presentation, provided that distinction must be made between a rat
caught and one found dead.
In transmitting a copy of this ordinance Consul G. H. Scidmore stated
that it was issued in accordance with the infectious diseases law of
Japan, No. 36, of March, 1897, which provides that cities, towns, and
villages shall make all necessary arrangements relating to the
extermination of rats as may be ordered by the prefectural governors.
He also stated that when the above ordinance was decreed the mayor of
Nagasaki issued detailed instructions regarding its enforcement. The
ordinance was enforced from the time of its enactment until July 7,
1908, when the city ceased paying bounties; from January 13, 1908, to
July 7, 1908, 980.33 yen ($488.20) having been expended, and 30,767
rats having been destroyed.
RAT EXTERMINATION IN LOURENÇO MARQUEZ, EAST AFRICA, AND MADAGASCAR.
In Lourenço Marquez, Consul W. S. Hollis states that a disinfecting
barge is maintained, and requisitioned from time to time by vessels,
by which means considerable numbers of rats are destroyed.
He also states that the last efforts to destroy rats on shore were
made during the plague outbreak in November and December, 1907.
In a circular accompanying Provincial Decree No. 754 of the
governor-general, the following relates to the destruction of rats:
1. For the destruction of rats we advise the public to make use of
poison paste.
2. These may be obtained by requisition on the municipal chamber and
from police stations.
3. The paste furnished shall be divided into portions and
distributed in different parts of the dwellings.
In Provincial Decree No. 737, issued December 11, 1907, by the
governor-general, it is required that grain and forage warehouses and
stables be provided with cement floors, and that ventilators be
provided with wire screens sufficiently fine to prevent the access of
rats, and that interior doors and salient angles be provided with
metallic points to prevent the climbing and entrance of rats.[CN]
Footnote CN:
Cases of pest in Lourenço Marquez, official report.
In Provincial Decree No. 48, issued by the governor-general January
30, 1908, it is proposed among other things to establish a permanent
service for the capture and bacteriological examination of rodents in
the city and its suburbs.
In transmitting the publication containing copies of these decrees the
consul stated that by the end of February, 1908, the campaign against
rats was relaxed, and since then nothing had been done to continue the
work of extermination.
In Tamatave, Madagascar, and other ports of that island no efforts
were being made to exterminate rats, and the American consul reported
that there were no municipal or colonial laws or regulations directing
such action.
RAT EXTERMINATION IN CAPE TOWN, SOUTH AFRICA.
In a report dated January 20, 1909, Dr. A. J. Gregory, medical officer
of health for the colony, states that at present no persons are solely
employed on rat catching, but the sanitary staff is required to take
all possible measures to reduce the rodent population. By the use of
bird lime a very large number of rats have from time to time been
destroyed. Doctor Gregory also refers to experiments made to determine
the value of tar and funnels placed on ropes to prevent the access of
rats to ships. The experiments were made to simulate actual conditions
that would prevail at ships lying at docks. It was found that thickly
coating a rope with fresh tar had not the slightest deterrent effect
on rats passing along. Funnels of a less diameter than 20 inches were
equally unsuccessful, and it was thought the experiments proved the
fallacy of trusting to tarred ropes or to disks of a workable diameter
being able to prevent rats from migrating in either direction between
shipping and shore.
RAT EXTERMINATION IN ALEXANDRIA AND CAIRO, EGYPT.
In Alexandria, Consul D. R. Burch stated that measures for the
extermination of rats were practiced; that the cost of disinfection
was defrayed by the municipality, which also supplied rat traps and
poison.
In Cairo rat destruction was being practiced, but it was stated that
the results could not be described as encouraging.
EXTERMINATION OF RATS IN THE PORT OF CONSTANTINOPLE.
Consul-General E. H. Ozmun, at Constantinople, states that while no
special measures have been taken to exterminate rats in that city, the
sanitary administration of the Ottoman Empire has provided measures
for the destruction of rats and mice on all vessels arriving from
places contaminated with plague, and he has furnished the following
copy of instructions concerning vessels which have or have not
undergone disinfection in view of destroying rats and mice on board:
ARTICLE 1. Vessels coming from places contaminated with plague and
which have not been disinfected either in the port of departure or
in an intermediary port during voyage, for the destruction of rats
and mice on board, according to the regulations of the superior
council of health, shall undergo their disinfection in the lazaretto
while finishing their quarantine.
ART. 2. Vessels coming from places contaminated with plague provided
with a certificate stating that the aforementioned disinfection has
been undergone may, after their admission, work in the port but
without landing on the quay.
ART. 3. Vessels proceeding from an uncontaminated Ottoman or foreign
port and which are provided with the certificate mentioned in
article 2 shall be free to moor at the quay if it is proved that the
vessel has been disinfected within a period of forty days; if not,
the vessel will operate in the port or at anchor.
Vessels in a similar case not provided with this certificate but
which can prove by the journal of the vessel that they have not
sailed within a period of four months to a contaminated port shall
be authorized to moor at the quay.
ART. 4. Vessels mooring at the quay must be at a distance of from 1
to 2 meters (39⅓ inches to 78¾ inches) maximum. During night they
must draw up the gangways and ladders, and must leave no towline
suspended without protecting it with funnels, brush wood, etc.
The vessels working in the harbor must also protect their towlines
in the same manner.
It is prohibited for lighters and boats to remain attached to these
vessels during the night outside of the time for working.
ART. 5. The above-mentioned vessels, mooring at the quay and on the
way to an Ottoman port, shall be required after having finished the
loading and discharging of cargo, to pass through the disinfection
prescribed by article 1 if their certificate of disinfection
mentioned by article 3 is found to be out of date, and also as long
as the city of Constantinople shall be considered as contaminated.
ART. 6. Vessels coming from uncontaminated quarters, although not
under any restraint, are free to go to any lazaretto in the Empire
and ask to be disinfected according to article 1; the latter will
work without delay so as to prevent loss of time as much as
possible.
ART. 7. The expenses of disinfection are to be paid by the vessels
disinfected.
ART. 8. Captains, doctors, or any officers of vessels are expected
to furnish the sanitary authorities with all information asked for
relating to the presence of rats and mice on board the vessel.
RAT EXTERMINATION IN RUSSIAN PORTS.
In Vladivostok, according to Consul Lester Maynard, the only efforts
to exterminate rats were made by the commissary department of the
army. Poisons, which had for their active principle caustic lime, were
distributed but were not entirely satisfactory, as the baits were not
sufficiently tempting food.
The keeping of cats had been recommended as the best method of
exterminating rodents, and it had been suggested that skunks, weasels,
and similar animals should not be killed, as they are the best
destroyers of rats and mice.
In Riga and Libau there were no laws and regulations prescribing a
systematic extermination of rats. The consul reported that only in
case of plague did the sanitary authorities order a thorough
destruction of rats not only on ships but also in warehouses and
private dwellings. The steamship companies, however, were said to
employ rat poison on their vessels, and, in addition, the ships were
thoroughly disinfected by means of sulphur fumes several times a year.
In Odessa it was reported by Consul J. H. Grout that the public health
officers of the port had been fully alive to the importance of
exterminating rats in order to prevent plague. In 1901 a systematic
extermination of rats on board vessels had been inaugurated, and in
1902 this practice was extended to include all vessels leaving the
port. The agent used in this process was the burning of sulphur in
specially designed iron containers. In 1902, 2,054 rats were killed in
346 vessels. In 1903, 1,038 rats were killed in 68 vessels. In 1904,
17,074 were killed in 168 vessels. In 1905, 512 rats were killed in
166 vessels. In 1906, 553 rats were killed in 188 vessels. In 1907,
1,887 rats were killed in 135 vessels; and in 1908, 1,138 rats were
killed in 97 vessels.
In St. Petersburg and vicinity no consistent effort, according to the
consul, had been made to exterminate rats, but at Cronstadt the port
authorities had experimented with ratin.
DESTRUCTION OF RATS IN TRIESTE, AUSTRIA.
All vessels arriving at Trieste from plague-infected countries on
board of which rats appeared in abnormal numbers were disinfected with
sulphur in accordance with rules of the Paris convention of 1903.
Consul G. M. Hotschick stated that it was a rule, whether rats were
numerous or not, to disinfect every vessel every six months so as to
exterminate rats on board. An exception was made in the case of the
Austrian Lloyd steamships plying between Trieste and the Far East,
these vessels being disinfected by the Clayton apparatus. All attempts
to destroy rats along the port shore had proven fruitless, according
to the consul, but in custom warehouses cats were kept, thus limiting
the number of rats.
The rules applying to Trieste extended to all the ports of Austria.
DESTRUCTION OF RATS IN GENOA, ITALY.
The methods employed at Genoa for the extermination of rats found on
ships were those prescribed by the ministry of the interior at Rome in
accordance with the Sanitary Convention of Paris.
As stated by Consul-General J. A. Smith, the regulations place all
ships arriving from plague-infected ports into three categories, as
follows: Infected, suspected, and noninfected. On ships coming under
the first two headings all rats must be destroyed previous to the ship
being allowed to pass quarantine. Noninfected ships were subject to
the same regulations only in case of an unusual mortality among rats
aboard, or in case of an excessive number of them being found on board
on arrival, which, in the opinion of the port medical officer,
required their destruction. Sulphur was used as the agent of
destruction, the gas being generated in a special apparatus. This
apparatus had been installed in the ports of Naples, Genoa, Messina,
Brindisi, Venice, and Asinara.
Further regulations of the ministry provided for the means to be
employed in preventing rats from reaching shore.
RAT DESTRUCTION IN BARCELONA, SPAIN.
In Barcelona Vice-Consul-General Wm. Dawson, Jr., reported that the
officials in charge of public health measures attached no really great
importance to the destruction of rats as an effective means of
preventing the spread of plague. Several attempts, however, had been
made to kill rats, which invade Barcelona to an enormous extent. In
his report the vice-consul further stated that bacterial cultures
known as _Tifus ratoso_, and supposed to have given excellent results
in Formosa, had been tried without appreciable results on wild rats.
He further stated that wheat boiled in a 5 per cent solution of
corrosive sublimate, dried in the air, and spread in sewers and other
places, had proved the most effective means of killing a few thousand
of them, but this practice had not been carried out to any great
extent nor for any length of time.
RAT DESTRUCTION AT FRENCH PORTS.
In Marseille the following was the practice as reported by the
director of the maritime health service at that port and forwarded by
Consul-General H. L. Washington:
The obligatory destruction of rats in all French ports is enforced
by virtue of a decree dated May 4, 1906. This applies: (1) To all
vessels arriving from a port regarded as contaminated by plague or
having only touched at such port. (2) To all vessels having received
in transshipment—that is to say, from ship to ship—merchandise
originating in a country deemed contaminated by plague. The
destruction of these animals is carried out exclusively by means of
apparatus whose efficacy has been recognized by the Superior Council
of Hygiene of France.
The devices employed at Marseille are:
(1) The “Marot,” adopted June 19, 1905. This apparatus utilizes
liquid sulphurous anhydrite, which is slackened, diluted in the air,
and subjected or not to the action of the electric spark. The gas is
introduced into the vessel by means of a ventilator at a rate of
from 25 to 30 meters per minute (82.02 to 98.42 feet).
(2) The “Gauthier-Deglos,” adopted February 18, 1907. This method
requires the combustion in an oven of a mixture of sulphur and coal
dust. A ventilator withdraws air from the vessel and causes it to
pass over the mixture in combustion; the gas thus produced is cooled
and then introduced into the vessel. A third device, known as the
“Clayton,” in use in some of the French ports, also operates from
time to time in Marseille on such vessels as are provided with it,
but it does not exist in the port itself. The principle of this
device is based upon the combustion of sulphur, its transformation
into sulphurous sulphuric gas, the cooling of the gases leaving the
oven, aspiration of the exterior air or the air in the holds of
vessels, and introduction into the holds by means of a powerful
ventilator.
With all three systems, the ships’ holds are opened only after they
have been in operation for three hours.
In Bordeaux, according to the consul, contracts had been entered into
between the Government and a private individual for the extermination
of rats on all ships coming from plague-infected ports, the apparatus
employed being that in use at Marseille.
In Havre the extermination of rats on vessels from plague-infected
ports was reported by Consul A. Gaulin as being systematically carried
out in accordance with a ministerial decree of May 4, 1906, which is
as follows:
ARTICLE 1.—The destruction of rats, or “deratization,” effected
exclusively by means of apparatus the efficiency of which has been
recognized by the Superior Council of Public Hygiene of France, is
obligatory for admission into French ports:
1. Of every ship coming from or having called at a port considered
as being contaminated with plague.
2. Of every vessel having taken in transshipment—that is to say,
from one vessel to the other—more than 50 tons of merchandise coming
directly from a country considered as being contaminated by the
plague.
The above provisions are applicable to vessels having already
discharged a part of their cargo in one or several foreign ports.
ART. 2.—May be exempt from deratization:
1. Vessels which only land passengers in French ports without
docking and which sojourn only several hours.
2. Vessels making a call of less than twelve hours and discharging
less than 500 tons of merchandise, on condition that the
surveillance of discharging be accomplished during the day
exclusively, the ship being moored away from the quays, and the
hawsers provided with rat guards.
3. Steamships which shall not have called at any port considered as
being contaminated by the plague for sixty days since their
departure from the last contaminated port, and on board of which
there shall have been observed nothing of a suspicious sanitary
nature.
4. Vessels which, having called at a port considered as being
contaminated by the plague, will prove that they neither berthed
alongside the quay or landing stages, nor embarked merchandise.
5. Vessels which have undergone the process of deratization in a
foreign port subsequent to their departure from the last port
considered as being contaminated. It must be proven, in this case,
that nothing of a suspicious sanitary nature has taken place on
board during the voyage, and that the deratization has been effected
with the same apparatus and the same guarantees as in France. The
captain of the vessel shall deliver as proof to the sanitary
authorities a certificate mentioning the apparatus employed, the
conditions under which the operation was effected, the verifications
made, etc., and a certificate viséed by a French consular officer.
6. Vessels whose status is that indicated in paragraph 2 of article
1, on condition that the merchandise has been transshipped from a
vessel which has been deratized under the conditions prescribed in
the preceding paragraph, and if such merchandise is accompanied by a
certificate of deratization provided for in said paragraph.
ART. 3.—Shall be considered as merchandise, for the application of
the present decree, all products embarked, figuring or not figuring
on the manifest, the only exception being coal embarked for the
needs of the ship without touching the quay.
ART. 4.—Deratization may be effected during the voyage by any French
ship having a surgeon, and one of the machines prescribed by article
1.
The sanitary official at the port of arrival shall determine, upon
examining the documents presented and the proofs furnished, the
conditions under which the operation has been effected, and he may
exact a total or partial renewal of the same.
The same provisions are applicable to foreign vessels, by virtue of
reciprocity, on the twofold condition that the sanitary officials of
the one (nation) enjoy the same standing as French sanitary
officials, and that the apparatus used are the same as those
mentioned in article 1.
ART. 5.—In ports, the deratization is effected before the unloading
of the ship.
The operation comprises the holds, bunkers, storerooms, crew’s
quarters, emigrants’ quarters or compartments for third and fourth
class passengers, and, in general, all interior compartments of the
ship.
The officers’ cabins, and those of first and second class
passengers, as well as the dining rooms, and saloons which are
provided for them, are not subjected to deratization except in cases
where the sanitary official judges it necessary—notably when the
ship is suspected of being or is infected by plague, when it has
been observed that the malady exists among the rats on board, or
when there has been a death from unusual causes.
ART. 6.—The apparatus to be employed for the deratization, by virtue
of article 1, are placed at the disposal of the owners or agents,
according to the conditions approved by the sanitary authority.
Ports possessing one of these machines are alone open to vessels
coming from countries considered as being contaminated by plague.
The operations are effected under the permanent supervision of the
sanitary authority and with the least possible delay.
ART. 7.—The expenses of deratization are borne by the owners, in
conformity with the provisions of article 94 (last paragraph) of the
decree of January 4, 1896. No sanitary tax is due, in consequence,
for the operation.
ART. 8.—The expenses considered in article 7 are based on the gross
tonnage of the ship, if the deratization comprises all its parts,
and on the cubic capacity of the parts deratized, if the operation
is partial. The cubic capacity is determined by and from the plans
of the ship, without allowing for the space actually occupied by
merchandise.
ART. 9.—A certificate setting forth the conditions under which the
operation has been effected is delivered to the captain or owners by
the sanitary authority.
ART. 10.—Ships which are not necessarily subject to the requirements
of deratization may, upon their request, be subjected to this
operation upon their departure, as on their arrival, either with
full or empty holds, and obtain, in consequence, the delivery of the
certificate mentioned in article 9. Every facility should be
accorded them for this purpose.
ART. 11.—Violations of the provisions of the present decree are
punishable by the penalties set forth in article 14 of the law of
March 3, 1822, independently of the measures taken for the isolation
or other measures to which ships are subjected by reason of their
origin or the sanitary condition on board at the time of arrival.
ART. 12.—Are annulled, the decree of September 21, 1903, and the
provisions of the decree of September 23, 1900, which would be at
variance with the second paragraph of article 6 above cited.
ART. 13.—The minister of the interior is charged with the execution
of the present decree, which shall be published in the Official
Journal, inserted in the Bulletin of Laws, and posted in the ports.
DESTRUCTION OF RATS IN GERMAN PORTS.
In Hamburg, according to Consul-General R. P. Skinner, stationed at
that port, persistent efforts were being made to exterminate rats not
only on board ship but in the city itself, and he reported the
following method of procedure:
Upon the arrival of every vessel an inspecting officer employed by
the board of health boards the same to inquire whether, during the
voyage, rats have died in exceptionally large numbers. While in port
the vessel is visited almost daily by inspectors, who search for
dead rats, particularly in the holds. On vessels from such ports
whence plague-infected rats have been brought to Hamburg repeatedly
an officer of the board of health is posted on board constantly to
watch the discharging of the cargo. All dead rats found are
immediately delivered to the Hygienic Institute; and if the latter’s
bacteriological examinations give reason to suspect plague, the
discharging is immediately discontinued and communication with the
shore interrupted. The vessel’s crew and discharging gangs are
placed under medical observation for a period of five days, the
cargo compartments are treated with generator gas, so as to
exterminate all rats, and, after the quarantine has been
discontinued and the cargo discharged, all compartments are
carefully disinfected. For the purpose of treating infected ships by
means of generator gas the Hamburg government owns a special
disinfection ship, called the _Desinfektor_, which will be described
later.
In order to exterminate rats on ships frequenting the port of
Hamburg the master of every vessel arriving here receives the
following instructions from a representative of the health officer
of the port:
He shall cause rat poison to be laid and fumigate holds by means of
sulphur and charcoal as soon as the cargo has been discharged, not
less than 10 kilos (22 pounds) of sulphur and 20 kilos (44 pounds)
of charcoal to be used for a room of 1,000 cubic meters (1,308 cubic
yards). Such rooms must be kept closed at least ten hours. On ships
arriving from ports infected with plague, rat poison is laid, free
of charge, immediately upon arrival, by an employee of the municipal
disinfection establishment, at all places within reach. On all other
ships the laying of rat poison is done by private persons whose
charges are payable by the vessel’s master or owner.
The disinfectors employed by the State of Hamburg use principally a
rat poison called “Rattengiftspeise,” consisting chiefly of
phosphorus and squills. Private rat killers may choose any other
material, but from time to time samples of such poisons as are laid
out on ships are taken by order of the harbor surgeon, and rats kept
in the public laboratories are fed with them, to enable a control as
to the effectiveness of the poison.
Under special circumstances the harbor surgeon is authorized to
waive the requirement of fumigation.
Killed rats are not permitted to be thrown overboard, but must be
delivered to the nearest police station, which causes their
cremation.
On river barges rat poison is laid by official disinfectors every
three months.
Finally there is rat poison laid, from time to time, in warehouses,
cargo sheds, and trade establishments in the harbor, partly by
official disinfectors and partly by private rat killers, which is
regularly controlled by the harbor surgeon, a special officer of his
department being engaged for such purpose.
The ship called the _Desinfektor_, owned by the government of
Hamburg for the purpose of disinfecting ships arriving from infected
ports and for the extermination of plague infected rats, is a
steamer equipped with a generator gas apparatus and other
disinfecting facilities. The method of using generator gas has been
chosen for reasons which are described in a booklet issued some time
ago by the local board of health on this subject.
In respect to the extermination of rats in Hamburg, aside from the
system adopted for ships and in the harbor, the consul-general states
that efforts to this end are being successfully carried out by
official disinfectors by order of the board of health, and he refers
to the procedures as follows:
If it becomes known to the board of health that in any locality or
group of buildings there are rats in large quantities, rat poison is
immediately laid. For such purpose the above-mentioned
Jungclaussen’s preparation is almost exclusively used. The several
local citizens’ associations (Bürgervereine), at the meetings of
which all topics of interest are discussed, contribute largely to
the bringing to the knowledge of the proper authorities of all
matters a remedy of which is, in public interest, considered
necessary, among them rat and mice nuisances in the several
districts of the city. Of late the board of health has also begun to
lay rat poison in houses in the old parts of the city, employing the
house-to-house method, and rat poison is laid, from time to time in
sewers and other underground canals where rats usually congregate in
large numbers.
As the laying of rat poison at or in the vicinity of places where
domestic animals are kept is dangerous to the latter, the Hamburg
board of health has only shortly ago caused a small gas generator to
be constructed, similar to that on the _Desinfektor_. The apparatus
can easily be removed from one place to another, and is chiefly to
be used on yards or unimproved lots, public parks, zoölogical
gardens, etc., where rats live under the ground. In fumigating such
a rat nest, all holes leading out of it are closed with earth,
except two. The hose of the gas apparatus is introduced into one of
the holes and gas insufflated. The majority of rats in the hole are
dead before being able to reach the fresh air. Those succeeding in
doing so, by getting out of the one open hole, are so dizzy that
they can easily be killed with a club. Only a few experiments have
so far been made with this apparatus, but the same promises good
success.
In Bremen, according to the consul, all disinfection of vessels and
their cargoes was done with sulphur dioxide by means of a Clayton
apparatus, and vessels equipped with this apparatus, and those having
physicians aboard, had the advantage of being able to start
disinfection twenty-four hours before arrival at port, this process
having been recognized as sufficient compliance with the quarantine
laws of Germany.
MEASURES AGAINST RATS AT THE PORT OF ROTTERDAM.
In the report from Consul-General S. Listoe it was stated that the
extermination of rats had not been officially undertaken by the
authorities of Rotterdam, either in the port or aboard incoming ships.
The question had been investigated, however, and the harbor master had
strongly advised the installation of a fumigating machine, which would
be installed on one of the numerous river police boats. Ship owners
had, for their own protection, caused their ships to be occasionally
fumigated, and two of the well-known lines had fitted out some of
their steamers with fumigating apparatus.
DESTRUCTION OF RATS AT ANTWERP, BELGIUM.
Consul-General H. W. Diedrich stated that no official action had been
taken in the port of Antwerp for the extermination of rats, but that
every vessel entering the port had to pass the sanitary station at
Doel, and there was authority to hold up any suspected vessel and to
insist on fumigation for the destruction of rats.
DESTRUCTION OF RATS IN DENMARK.
As a result of the agitation started in 1898, the following law was
passed and signed by the King of Denmark on March 22, 1907:
1. When an association constituted for the purpose of effecting the
systematic destruction of rats has proved to the satisfaction of the
minister of the interior that it is in a position to expend on the
furtherance of its objects, within a period of three years, a sum of
not less than 10,000 kroner per annum, it shall become incumbent
upon each local authority to make suitable arrangements at the
expense of the local funds, and commencing with a date to be made
known hereafter by the minister of the interior, for the reception
and the destruction of all rats killed within the district of such
authority and delivered up to such authority.
For each rat delivered up each local authority shall pay a premium,
for the payment of which an annual grant shall be made out of the
local funds, which shall be not less than three kroner per each
hundred inhabitants within the district of each local authority,
according to the then last general census.
The State shall make for a period of three years an annual grant of
30,000 kroner, of which one-third may be expended on scientific
experiments with preparations for the extermination of rats, under
the control of, and in consultation with, the Royal Veterinary and
Agricultural College, while the remainder shall be expended on
purchasing preparations for the extermination of rats, which shall
be either employed on or in public lands or buildings, or out of
which remainder grants may be made to associations toward the
purchase of such preparations, in a manner to be defined hereafter
by the minister of the interior.
2. Each local authority shall fix the amount of the premium (sec. 1)
which shall not, however, be more than 10 oere or less than 5 oere.
Instructions for the collection and destruction of the rats killed
will be issued by the minister of the interior.
3. The association cited in section 1 shall submit for the sanction
by the minister of the interior at the beginning of each year a plan
showing the proposed expenditure, and at the end of each year an
account of the money expended by it, together with statistics
obtained by it showing the expenditure on premiums made by each
local authority.
4. Where the proprietor or occupier of a messuage has participated
in the grant to be made by the State (sec. 1), he shall not deliver
up, or cause to be delivered up, for the purpose of obtaining a
premium or premiums, rats killed within the said messuage, until the
expiration of one month from the employment of such preparation for
which such grant has been made. Any person acting in contravention
of this section shall be liable to a penalty of 100 to 500 kroner.
5. Any person who preserves or breeds rats or imports rats from
abroad, in order to obtain premiums or enable another person to
obtain them, shall be liable to a penalty of 100 to 500 kroner,
unless he is liable to a higher penalty under the common law. A
person who shall deliver up rats knowing them to have been
preserved, bred, or imported for the purpose of obtaining a premium
shall be liable to the same penalties.
All proceedings under this act shall be taken in a public police
court, the fines to go to the special funds provided by this act, or
where such fund does not exist, to the public funds of such local
authority.
Any person delivering up rats to any other local authority than to
that within the district of which they have been caught shall be
liable to a penalty not exceeding 100 kroner.
This act shall come into operation on a date to be fixed hereafter
by the minister of the interior and remain in operation for three
years.
In the session of the Riksdag immediately preceding the expiration
of this law a vote shall be taken for the renewal or revision of
this law.
The Government is authorized by royal rescript to make such
alterations in the operations of this law within the Faroe Islands
as may be considered most suitable, having regard to the special
conditions obtaining within those islands.
Following the enactment of this law, there was issued by the ministry
of the interior May 1, 1907, a circular to the local authorities on
the subject.
CIRCULAR TO THE LOCAL AUTHORITIES.
Whereas the Association for the Authorized Extermination of Rats has
proved to the satisfaction of the ministry of the interior that it
is in a position to expend on the furtherance of its objects not
less than 10,000 kroner within a period of three years, it is hereby
requested, in pursuance of act No. 59, of the 22d March, 1907 (see
public notice dated this day), and commencing with the 1st day of
July of this year each local authority shall at its own expense take
all such measures as may be necessary for the reception and
destruction of all rats killed within the district of such authority
and delivered up to it. For the purpose of paying a premium for each
rat delivered up each local authority shall out of the common funds
make an annual grant which shall be not less than 3 kroner for each
hundred inhabitants, according to the then last general census,
should the amount required for the payment of premiums make such
grant necessary. It shall be left to each local authority to decide
whether further grants shall be made toward this purpose. The
premium to be paid for each rat delivered up shall not be more than
10 oere or less than 5 oere, and shall be fixed by each local
authority which shall give due and sufficient notice both of the
date fixed for the commencement of the operations of the law and the
premium to be paid. As far as possible, a uniform rate of payment by
premium shall be fixed by local authorities within the same county.
Rats may not be delivered up to any local authority but to that
within the district of which they have been caught; any person
acting in contravention (par. 5 of the aforementioned law) shall be
liable to a penalty not exceeding 100 kroner.
The chairman of the councils of the various local authorities are
hereby requested to take steps for the discussion and carrying out
of the provisions of this law.
If the grant made by any local authority for the purposes of this
law should prove insufficient for the payment of premiums on all
rats delivered up, such authority may apply to the Association for
the Authorized Extermination of Rats, Colbjornsengade 14, Copenhagen
B, for a subsidy, this association having undertaken to organize the
obtaining of voluntary subscriptions for the carrying out of the
purposes of this act.
The said association is further prepared, at the request of local
authorities, to render expert assistance in commencing and carrying
through operations under this act.
For the collection and destruction of rats killed the ministry of
the interior issues the following instructions:
A.—THE LARGER TOWNS.
_Collecting depots._—The local authorities shall provide a
sufficient number of places suitable for collecting depots. Such
depots must not be within any place where food or clothing is made
or offered for sale. Fire brigade stations are considered most
suitable for collecting depots.
The collecting may suitably be done in the manner that for each
depot a number of receptacles are provided, made of galvanized iron
and furnished with a tight-fitting lid. Into these receptacles the
rats are to be thrown after their tails have been cut off. The tails
are to be kept in a separate tin box. All receptacles and boxes are
to be collected daily and to be replaced by empty receptacles. The
full receptacles are to be taken to the place where the destruction
of the rats is effected.
Further advice on the purchase of such receptacles and the apparatus
for cutting off their tails will be given by the Association for the
Authorized Extermination of Rats at the request of a local
authority.
The destruction may be effected either by cremating the dead
rats—for instance, at the municipal gas works—or by burying the
carcasses in the open, at a sufficient distance from the town,
unless this course is prohibited by local sanitary considerations.
It is recommended that the local authority act in this manner always
with the local health committee.
B.—THE SMALLER TOWNS.
Instead of opening a fixed depot, it would appear more suitable in
the smaller towns to provide a collecting cart. Any horse-drawn
vehicle would serve the purpose as long at it is furnished with a
fixed apparatus for cutting off the tails and a receptacle of
galvanized iron for receiving the carcasses of the rats. The vehicle
should also be fitted with a bell, to announce the arrival and
presence of the collecting cart.
The destruction of the carcasses is to be effected in the manner
described under A.
C.—THE VILLAGES.
The authorities in the villages shall appoint a suitable person to
receive the rats delivered up, for which work he shall be paid an
adequate remuneration. Such persons must be supplied with an
apparatus for cutting off the tails of rats handed in. After the
tails have been cut off, the rats may be buried in a suitable place
without delay. It is most undesirable that any person engaged in the
carrying of milk or other foodstuffs be asked to convey rats to the
persons appointed to receive them. Villages in close proximity to
towns are advised to make arrangements for the cremation of the rats
at the municipal gas works.
In the case of villages whose buildings approximate those of a town
it is recommended that the regulations given for towns are adopted.
Respecting the payment of the premiums it is recommended that the
person in charge of a collecting depot or otherwise appointed to
receive rats is supplied with a fixed amount of petty cash, out of
which he pays the premium for each rat delivered up. The tails cut
from the rats serve as a receipt for the payment made, so that the
total amount of tails will be a discharge for the total amount of
petty cash received and paid out in premiums.
In order to prevent abuse it is particularly requested that the
local authorities take care that the rat tails are destroyed in an
efficient manner as soon as they have served the purpose of control
and checking.
For the purpose of keeping satisfactory accounts the Association for
the Authorized Extermination of Rats has on sale specially arranged
account books which are recommended by the ministry of the interior.
As in accordance with paragraph 3 of the law of 22d March, 1907, it
is the duty of the Association for the Authorized Extermination of
Rats to submit to the ministry of the interior a report on the money
expended in the whole of the kingdom on such premiums, the local
authorities are hereby desired to make a quarterly return to the
aforementioned association on the number of rats killed within the
district of each authority in each month of the quarter covered by
such return and on the money paid out for premiums. Forms for such
returns will be supplied by the association.
Any associations which in accordance with terms of paragraph 1 of
the law of 22d March, 1907, desire to participate in the grant made
by the State for the purpose of purchasing preparations for the
extermination of rats (ratin, etc.) must send a request to that
effect to the minister of the interior, together with a statement
showing the approximate cost of the proposed campaign and the amount
at the disposal of the association for that purpose. As this law is
essentially of an experimental character, the requests of all such
associations will be treated as preferential, which show that the
proposed extermination may be easily and successfully effected (as,
for instance, on small islands).
A number of copies of this circular will be forwarded to each local
authority.
DESTRUCTION OF RATS IN SWEDISH PORTS.
Consul W. H. Robertson at Gothenburg, Sweden, quoted the city
physician to the effect that “upon the appearance of plague in Great
Britain the city council decided in April and November, 1901, to make
an appropriation of $2,680 for an attempt to reduce the number of rats
within the community.” These attempts were continued during the period
May, 1901, to September, 1902, 2.68 cents being paid for each rat
caught. Any unusual mortality among rats on board a vessel coming from
a plague-infected port was being dealt with in accordance with a royal
proclamation of June 16, 1905.
In Malmo, according to the consular agent, the authorities during the
past seven years had given a premium for every rat killed during the
first five years, 2.68 cents for each rat, but during the past two
years only half of that amount.
DESTRUCTION OF RATS IN ENGLISH PORTS.
The Local Government Board has issued regulations for the prevention
of plague and certain other diseases. One of these regulations is as
follows:
The master of a ship which by reason of plague is an infected ship,
or a suspected ship, or which has come from, or has during the
voyage called at, a port infected with plague, or in which there are
rats infected with plague, or in which there is or has been during
the voyage an unusual mortality among rats, shall, under the
direction and to the satisfaction of the medical officer of health,
take all such precautions or employ all such means for effectually
stopping the access of rats from the ship to the shore as in the
opinion of the medical officer of health are measures reasonably
necessary for the prevention of danger arising to public health from
the ship.
In accordance with this regulation, notice was given in a circular
issued by the medical officer of health of the port of London of the
precautions necessary for stopping the access of rats from ship to
shore in that port. These precautions were outlined as follows:
1. All ropes and mooring tackle for securing the vessel either to
the shore or mooring buoys shall be fitted with metal brushes,
funnels, or other effective guards, the portions of such ropes and
mooring tackle leading from the vessel to a distance from the
vessel’s side of at least 4 feet shall be coated each night with
fresh tar. Ropes may, if desired, be protected by a covering of
canvas or yarns before tarring.
2. When not engaged in discharging cargo, one gangway only shall be
permitted to afford means of communication between the ship and the
shore.
3. The end of the gangway near the ship shall be whitened for a
length of 10 feet, and the watchman shall keep the gangway pulled
inboard after sunset, or it shall be guarded in some approved
manner.
4. When alongside the quay, the ports on the side of the vessel
nearest the quay shall be kept closed after sunset.
5. All empty cases and barrels, especially those from the
storerooms, shall be examined before being landed, to insure that no
rats are contained therein.
6. It is recommended that all possible means be adopted for catching
and destroying rats, both on the voyage and during the stay of the
vessel in port. Any rats so caught shall be killed, then placed in a
bucket of strong disinfecting solution, and afterwards burnt in the
ship’s furnace.
7. No rats, alive or dead, are to be removed from the ship without
my permission in writing.
In London, the practice of destroying rats on the docks had been
systematically carried out by the dock companies at their own expense
and under the supervision of the port sanitary authority. Vice-consul
Richard Westacott reported that the destruction of rats on vessels was
provided for by regulation whenever the medical officer of health was
satisfied that such precaution against the introduction of the spread
of plague was necessary.
In Liverpool, Consul J. L. Griffiths stated that earnest endeavors
were made to capture rats by professional rat catchers. On infected or
suspected ships, special precautions were taken to prevent the escape
to the shore of rodents. On noninfected or nonsuspected ships the
medical officer of health might also require the destruction of rats,
and in this case the expense was borne by the sanitary authority. It
is evident, therefore, that the precautions taken are in accordance
with the provisions of the International Sanitary Convention of Paris.
It was the practice, at the time the consul sent his dispatch, to
maintain strict surveillance over vessels likely to develop plague
aboard until after the period of incubation had been passed.
In Southampton, according to Consul A. W. Swalm, a competent man was
employed by the dock authorities whose sole duty was to wage war on
rats. In addition, the night watchmen on all vessels were required to
perform the additional duty of trapping rats. The usual precautions to
prevent the passage of rats from ship to shore were also observed.
MEASURES AGAINST RATS AT AUSTRALIAN PORTS.
The following are the regulations issued under the quarantine act of
1908 by the commonwealth of Australia relating to the ingress to and
egress from vessels of rats and mice; the destruction of rats, mice,
and other vermin; and precautions against the introduction of vermin
from plague-infested places.
136. (1) The master or owner of every vessel shall—
(_a_) Effectively obstruct—against the migration of rats—by means of
stout wire netting, all pipes, ports, cabin scuttles, and other
openings or holes in the side of the vessel next to the wharf, and
also when cargo is being discharged into lighters, in the side next
to the lighters, and keep them so obstructed while the vessel is
alongside the wharf or lighters;
(_b_) Prevent any organic refuse, galley scraps and waste from being
discharged into the waters or on the wharfs of any port.
(2) The master or owner of any vessel arriving in any port in
Australia from any place proclaimed infected with plague, or as a
place from or through which plague may be brought or carried, under
section 12 of the quarantine act, 1908, shall—
(_a_) Produce to the quarantine officer a certificate showing that
an efficient fumigation of such vessel while empty had been carried
out prior to departure. Such certificate, in the case of an oversea
vessel, must (if the port of departure be within the British
dominions) be signed by the health officer of the port; or, when
such port is a foreign port, by the British consul. In the case of
an interstate vessel the certificate must be signed by a quarantine
officer. In the absence of such certificate the quarantine officer
may require the cargo to be discharged in the stream. Efficient
fumigation in this regulation shall mean fumigation as specified in
regulation 137 (2) _b_;
(_b_) Suspend or cause to be suspended over the side of the vessel
against the wharf, or against any lighter alongside, electric or
other effective lights, distributed so as to afford from sunset to
sunrise thorough illumination fore and aft along the whole side of
the vessel.
137. (1) The owner or master of any vessel shall—
(_a_) Keep all foodstuffs and food refuse in rat-proof and
mouse-proof receptacles;
(_b_) Thoroughly flush out and afterwards empty the bilges before
berthing at any port;
(_c_) Keep on board the vessel a dog or a cat—or both—efficient for
rat and mouse killing, and give it or them constant access to those
parts of the vessel where rats or mice may harbor;
(_d_) Set and keep set in sufficient numbers and in suitable places
metal break-back traps or other effective traps for rats and mice;
and
(2) When so ordered by a quarantine officer, shall—
(_a_) Lay on the vessel poison baits effective for rats and mice;
(_b_) Submit the holds and other such parts of the vessel as the
quarantine officer directs to sulphur fumigation in accordance with
this regulation, or to some other method of fumigation approved by
the director of quarantine. Sulphur fumigation shall be effected by
passing sulphur fumes into the vessel under pressure, and at the
same time exhausting the air in the parts of the vessel under
fumigation, and shall be continued until all parts of the vessel
under fumigation are filled with a gaseous mixture of a strength of
not less than 3 per cent of sulphur oxides, and are kept so filled
for at least eight hours.
The fumigation shall, if the quarantine officer so orders, be
carried out in the stream or away from a wharf.
(_c_) Clean, wash, or spray all portions of the vessel likely to
harbor or afford shelter to vermin, with an approved insecticidal
solution effective for the killing of fleas, lice, bugs, and other
vermin; and
(_d_) Flush, cleanse, disinfect, or empty all lavatories, water
tanks, or any closed-in space on board the vessel, and cause to be
produced for disinfection any articles desired by the quarantine
officer.
In Sydney, it was stated by the president of the department of public
health that steady, systematic poisoning and trapping of rats were
done all the year round, and that this had been the case for the past
eight years. The experience there had been that mineral poisons were
found to answer best, and that organic viruses had been found to be
not practically successful.
In Melbourne, rat destruction was carried on by the board of public
health of Victoria and by the local health authorities under the
Victorian health act of 1890. As stated in the report of Consul J. M.
Jewell, the board of public health restricts its operations to
shipping wharves, to shores, and banks of the River Yarra upon which
Melbourne is situated. Since 1900, the board had had a staff of men
continually engaged in distributing poison baits. In order to prevent
the passage of rats to and from vessels, certain specific berthing
restrictions were in force. In addition, fumigation of vessels was
practiced under the supervision of the board’s officers. The board had
continually urged the various municipal authorities to maintain the
crusade against rats and render dwellings rat proof.
The consul also stated that the local municipal councils paid a bonus
for every rat, and that the fee was then 4 cents.
In Adelaide, it was stated there were no compulsory regulations for
the destruction of rats, but shipping companies had cooperated with
the local sanitary authorities to keep down these rodents on the
wharves by means of poison and traps, the poison being supplied gratis
by the board of health.
In Fremantle, and other seaports of Western Australia, according to
the consul-general, men were engaged in baiting and trapping rats,
these precautions being maintained throughout the year.
MEASURES AGAINST RATS IN SOUTH AMERICAN PORTS.
In Buenos Aires it was stated by the chief of the asistencia publica
that a regular staff of 150 men was employed in the destruction of
rats and fumigation of houses. A map of the city showing houses that
had been found to contain rats was marked. In addition, a pesthouse
was maintained in which live rats were watched, and developments of
pest noted.
In Montevideo Consul F. W. Goding stated that there were no organized
efforts for the destruction of rats, but that vessels were fumigated
at stated intervals under the direction of the sanitary authorities.
He also stated that the Government had required portions of the sea
wall to be covered with cement in order to prevent rats obtaining a
lodging there.
In Callao, Peru, provision was made for the fumigation of vessels from
infected ports, and it is stated by Consul-General S. M. Taylor that
the Government had required steamship companies to install fumigating
apparatus on board their passenger vessels.
It is stated by the consul that there was a new municipal law in
Callao calling for stone or brick 2 feet below and 2 feet above ground
on all walls and foundations for new buildings, and concrete floors in
all establishments where provisions are sold.
In Iquique, Chile, it was reported by the consul that the director of
the municipal laboratory disinfected houses infected with plague, and
sent a corps of men to poison and trap rats which might be therein.
MEASURES AGAINST RATS IN WEST INDIAN PORTS.
From Habana it was reported that no action had been taken by the
sanitary authorities toward exterminating vermin, except the
promulgation of a circular letter calling attention to the presence of
the plague in neighboring countries, and requesting citizens to free
their premises of rats. The same statement was also said to apply to
other Cuban seaports.
In Kingston, Jamaica, on account of the appearance of the plague in
Venezuela, the government took precautionary measures with the view of
exterminating rats. These steps, as reported by Vice-Consul W. H.
Orritt, were as follows:
A. Lectures were delivered in various centers of the island showing
how rats are the distributers of plague and the necessity of
destroying them.
B. Virus was imported, and live rats were inoculated and set free in
every seaport in the island.
C. Bamboo pots with poison glued to their bottoms were distributed to
householders and placed in the haunts of rodents.
In Santo Domingo bounties for rats were authorized May 19, 1908, by
the city council. In addition, rat virus had been used in considerable
quantity.
DESTRUCTION OF RATS IN PANAMA.
In Cristobal, Canal Zone, Colon, and Bocas del Toro, it was stated by
Consul J. A. Kellogg that the sanitary department of the Isthmian
Canal Commission had for some time been exterminating rats by traps
and poisons.
In La Boca, Canal Zone, Consul-General Arnold Shanklin stated that the
sanitary department of the Isthmian Canal Commission and the Public
Health and Marine-Hospital Service had in charge and had most
effectually carried on the extermination of rats, and that this
crusade had also been extended to the old docks and wharves in the
city of Panama.
MEASURES AGAINST RATS IN VANCOUVER.
It was stated by Consul-General George M. West, December 17, 1908,
that the city of Vancouver was paying a bounty of 50 cents per hundred
for all rats caught. The following regulations for the docking or
mooring of vessels arriving from plague-infected ports became
effective April 8, 1908:
1. All vessels arriving at British Columbian ports from ports
infected or suspected of being infected with bubonic plague shall
conform to the following regulations:
(_a_) Vessels shall be moored or docked at a distance not less than
6 feet from wharf or land.
(_b_) Ropes or chains connecting a vessel with wharf or land shall
be protected by funnels of size and shape satisfactory to local and
provincial boards of health.
(_c_) All gangways shall be lifted when not in use. Gangways when in
use shall be guarded against the exit of rats by a person specially
detailed for this purpose.
(_d_) All vessels changing route to solely British Columbian ports
shall give satisfactory evidence of disinfection and extermination
of vermin to provincial board of health.
2. Every owner, agent, or captain of any vessel, and every other
person violating or instructing, authorizing, ordering, permitting,
or otherwise suffering any person to violate any of the foregoing
regulations, shall be liable, upon summary conviction before any two
justices of the peace, for every such offense to a fine not
exceeding $100, with or without costs, or to imprisonment, with or
without hard labor, for a term not exceeding six months, or to both
fine and imprisonment, in the discretion of the convicting
magistrates.
Dated at Victoria, 8th April, 1908.
In addition, the mayor and council of the city enacted a by law
November 11, 1907, one provision of which made it unlawful for any
boat entering the port of Vancouver to be connected with any wharf in
the city by a gangway which was not guarded by some person there for
the purpose of preventing rats from leaving such import by such
gangway.
NECESSITY OF CONCERTED ACTION OF NATIONS.
It appears from the foregoing data that a more or less widespread
crusade against rats is being carried on in the different ports of the
world, and that the extent and persistence of these measures, with few
exceptions, depend upon whether the particular port has been directly
threatened with an invasion of plague. It is necessary to state here
that the above data are not presented as a complete epitome of
measures taken throughout the world, but refer to the ports from which
consular reports were received.
The fact that within fifteen years plague has spread to no less than
52 countries indicates that the measures taken against rats have not
been wholly efficient.
It is too much to expect that the rat population can ever be
exterminated from any country, but by the adoption of systematic
measures, such as are in force in Denmark, the rat population should
be markedly reduced, and the occurrence of plague among rodents
quickly detected. It is not too much to expect, however, that ocean
carriers could be freed from rodents and kept so, and this action
would confine plague within continental boundaries.
When the existing sanitary conventions were adopted several years
since, the importance of the subject was just beginning to be
recognized, but now that the rat has been proven beyond all doubt to
be the greatest factor in the transmission of plague from one country
to another it would appear that the conventions in question should be
amended, and the Surgeon-General of the Public Health and
Marine-Hospital Service, in a communication of February 26, 1909,
addressed to the Secretary of State, suggested the advisability of
submitting the question of the systematic destruction of rodents
aboard ships to an international sanitary conference with the view to
the adoption of an international sanitary regulation on the subject.
It must be apparent that such a regulation would lessen quarantine
restrictions, prevent the destruction of cargo by rodents, and in
large measure obviate the danger of the further spread of plague.
------------------------------------------------------------------------
TRANSCRIBER’S NOTES
Page Changed from Changed to
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affection in man known as favus affliction in man known as favus
57 This specie of Mus is very This species of Mus is very
susceptible to a large number of susceptible to a large number of
bacterial bacterial
59 Rabinowitch, L., ’03. Ueber ein Rabinowitch, L., ’03. Ueber eine
Hauterkrankung der Ratten. Cent. Hauterkrankung der Ratten. Cent.
f. Bact., f. Bact.,
144 Universitat zu St. Petersburg. Universität zu St. Petersburg.
● Typos fixed; non-standard spelling and dialect retained.
● Used letters for footnotes and numbers for endnotes. Renumbered all
to avoid duplicates.
● Enclosed italics font in _underscores_.
● Subscripts are shown using an underscore (_) with curly braces { },
as in H_{2}O.
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