Chapter VIII: Part 8

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.