160 REVIEW — TROPICAL MEDICINE, ETC. 



Plague — plague on the strength of the macroscopical appearances alone, oven though the other results 

 continued of cutaueous inoculation and culture are negative, and the animal shows marked signs of 

 putrefaction. 



The value of the method of cutaneous inoculation of guinea pigs has been examined ; it 

 would appear to fail only in about 2 per cent, of fresh, and about 10 per cent, of putrid, rats. 



The bacilli found in naturally infected rats are fully virulent, 02 per cent, of the 

 inoculated animals die of acute plague in five days or less. A well-illustrated paper on the 

 pathological histology of the spleen and liver in spontaneous rat-plague, which follows the 

 above, will repay perusal. Eats were fed with infected material, and it was found that : — 



1. It is possible to infect wild rats of Bombay with plague by feeding them with the viscera of dead 

 plague rats, 21'4 per cent, being susceptible to this method of infection. Bombay rats show a greater immunity 

 to infection by feeding than rats of the same species, which have not been subjected to a plague epizootic. 



A series of experiments were also done with Mus ratlus caught in the Punjab. Of these rats 67'8 per cent, 

 were susceptible. In this series a considerably larger dose of infected material was given. 



We have infected a large number (38 per cent.) of wild Bombay rats by feeding them on the whole 

 carcases of their plague-infected comrades. No difference as regards the post-mortem appearances or the 

 distribution of the primary bubo was found between rats infected in this way and rats infected by feeding on soft 

 viscera. 



2. The general pathological lesions found in all rats infected by feeding are, in the main, the same as 

 those found in rats naturally infected. There are, however, two striking differences : — 



(ff) The distribution of the prim.ary bubo is different. The common site in naturally infected plague rats is 

 in the neck, no mesenteric bubo having been seen out of 5000 post mortems. In the case of fed rats the common 

 site is the mesentery. 



(6) In the case of naturally infected rats the stomach and intestines show no marked pathological change. 

 In the case of fed rats well marked pathological lesions are found in the intestines. 



3. It would appear that in nature intestinal infection rarely or never takes place, and that in consequence 

 rats do not become infected by eating the carcases of their comrades. 



4. A large series of rats were fed on the urine of plague cases. None of these contracted the disease. 

 Most important of all, perhaps, are the extended observations on the transmission of 



plague by fleas and the fate of the plague bacillus in the body of the rat flea (T. cheopis). 

 Thus :— 



1. The average capacity of a rat flea's stomach is approximately O'O c.c. On this basis a flea imbibing the 

 blood of a plague rat showing a good septicaemia might take as many as 5000 germs into its stomach. 



2. Multiplication of the plague bacillus takes place in the stomach of the rat flea. 



3. The approximate proportion of fleas in the stomach of which multiplication of plague bacilli takes place 

 has been determined, and it has been shown that this proportion varies with the season of the year, being six times 

 greater in the epidemic season than in the non-epidemic season. 



4. Plague bacilli are present in the rectum and fiEces of fleas taken from plague rats, and such faeces are 

 infective to guinea pigs both by cutaneous and by subcutaneous inoculation. 



5. On rare occasions plague bacilli have been found in the oesophagus, but never in any other region of the 

 body, such as the body cavity or salivary glands. 



6. During the plague season fleas might remain infective for 15 days after imbibing infective blood, but 

 during the non-epidemic season no animal was infective after the 7th day. 



7. A single rat flea may transmit the disease. 



8. Both male and female rat fleas can transmit the infection. 



9. Experimenting with cat fleas ('P. /cZ/s^ and human fleas f/". irritans), 27 experiments with the former were 

 unsuccessful, and out of 37 experiments with the latter three successes were obtained. Two experiments were 

 made with C'.fascialas ; both were successful. Multiplication of the plague bacillus takes place in the stomach of 

 the human flea. 



10. The plague bacillus has never been seen in the body cavity or in the salivary glands of infected fleas. 

 Evidence has been obtained to show that the bite of a healthy flea affords a suflicient avenue for infection by 

 septicaemic blood if it be spread upon the bitten part. No evidence has been obtained in favour of infection by 

 contaminated mouth parts or regurgitation from the stomach, but the possibility of infection by such means 

 cannot be excluded. 



There is also a paper on the differentiation of the rat flea from other fleas. 

 As regards the epizootic amongst rats, the following points were determined : — 



1. Mas decumanus and Mus rattua are equally susceptible to plague. 



2. The incidence of plague is twice as great on the decumanus population as on the rattus population. 



3. Mas decumanus is the species which is chiefly responsible for the diffusion of plague amongst the rats 

 throughout Bombay City. 



4. The decumanus epizootic precedes the rattus epizootic by a mean interval of about ten days. 



5. The rattus epizootic is directly attributable to the dccamanus epizootic. 



6. Plague persists in the rats in Bombay City during the off season. This persistence is due chiefly to 

 M. decwiMnus. 



