BACTERIOLOGY OF PLAGUE.]
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If a rat is artificially inoculated with a very minute quantity of a virulent plague cul-
ture, death generally ensues in 24—48 hours. After about 10 or 12 hours the rat looks
very ill. It sits huddled up in a corner of its cage, and is disinclined to move or eat.
Difficulty of breathing gradually supervenes, and increases in amount until suddenly
about half an hour before death the animal falls on its side in extreme prostration.
Convulsive dyspnoea, twitchings of the limbs and tail, rapid and strong at first, but
quickly weakening, cease in death. Fasces and urine arc voided involuntarily and not
infrequently a paralysed condition of the lower limbs is obvious long before the final
seizure.
On opening the animal a hæorrhagic ædema at the seat of inoculation is noticeable.
Similar conditions often exist in the inguinal, cervical, and axillary regions, but glandular
enlargements arc seldom, if ever, visible to the naked eye. The heart is engorged with
dark fluid blood, teeming, as a rule, with plague-bacilli. The lungs ace collapsed and
show pneumonic patches. Drs. Gibson and Ransome have observed in rats appearances
similar to that of true pueumonic plague in man. The liver and spleen are both enlarged.
The latter is often double its normal sise. Bacilli are easily demonstrable in these organs.
The bladder is frequently distended with, urine, and in a few instances plague-bacilli have
been obtained from this source.
In a country like India, where the decomposition of organic matter is accelerated by
climatic conditions, putrefactive bacteria rapidly outgrow the plague-bacilli, and after 12
hours at the most the chances of isolating the plague-bacilli by culture from such, organic
matter are very remote.*
Klein and other observers remark that passage of the bacillus through several animals
of the same species has the effect of increasing the virulence of the micro-organism, at least
for that species. Dr. Balfour-Stewart t has recently noted that if a series of rabbits be
inoculated with increasing doses of a 10 days' culture of living plague a greater proportion
of those receiving a large dose survive, than of those injected with the smaller quan tities.
This he thought due to the fact that the larger doses contained a larger amount of
immunising constituent, and so rendered the inoculated animal immune to the microbes
contained in the culture injected.
Dogs, eats, horses, cattle, sheep and goats are not susceptible to plague; although
inoculation with plague cultures causes in them a distinct febrile and local reaction. Goats
appear to suffer most. Not infrequently they slowly sicken and die—a fact which has
been occasionally observed in rabbits also.
Birds are apparently immune. Sick pigeons and crows have been examined at the
Laboratory, but the plague-bacillus has never been isolated from them.
The rôle of insects in the propagation of disease is attracting attention. In relation
to plague, Yersin has stated that he has found the bacillus in flies, while the German.
Plague Commission infected guinea-pigs with an emulsion made from fleas taken off a rat.
Our knowledge of the plague-bacillus outside the bodies
The Plague bacillus in Nature.
of affected animals and apart from the artificial conditions
already detailed is practically nil.
* Corthorn and Milne in the Indian Medical Gazette for May 1899.
† British Medical Journal, 2nd September 1899.
‡ The reports received therefore of cases of plague amongst, oats would appear to be incorrect ; no
bacteriological examination having been made.