

vi PLAGUE INDUCED IN OTHEE EODENTS 137 



centage of cases only slightly enlarged or not appreciably so, as will 

 readily be understood from the description of the microscopic 

 examination of the organ : not only was there found stasis and 

 coagulation of the blood in most vessels, but also a distinct shrinkage 

 of the Malpighian corpuscles due to necrosis. The number of bacilli 

 in the spleen was small and not to be compared with what is the 

 general rule in the case of the virulent type of plague. As regards 

 the liver, lung, and kidneys, the absence of any appreciable number 

 of B. pestis appears a noteworthy feature. 



Since the inguinal bubo (i.e. the proximal local effect) contains 

 just as vast an amount of B. pestis as in the case of the virulent 

 type, the conclusion is justified that in the attenuated type the 

 condition of the organs (congestion, haemorrhage) is mainly toxic ; 

 that is to say, is due to absorption into the circulation of the toxin 

 formed in the bubo by the B. pestis. Further, it appears that in its 

 attenuated type B. pestis does not find in the viscera suitable con- 

 ditions for its existence and multiplication as does the B. pestis of the 

 virulent type, and that owing to B. pestis of the virulent type 

 thriving and multiplying well in the viscera the amount of toxin 

 circulating in the system in animals inoculated with it must be 

 greater than in the case of the attenuated type. This would not 

 only account for the more rapid course and more rapidly fatal issue 

 of the disease in the former case, but would seem to indicate that in 

 the attenuated type the delayed death permits sustained action of the 

 toxin, enabling it to produce the conspicuous necrotic changes in the 

 bubo, in the spleen, and in the liver upon which stress has been laid. 



One further important consideration deserves notice — namely, 

 that owing to the generally copious presence of B. pestis in the 

 vessels of the viscera (lung, intestine, kidneys) of animals inoculated 

 with the virulent type, the excretions of these rats would be liable 

 to be charged with the contagium and to be to a corresponding extent 

 dangerous ; whereas with the attenuated type the excretions of the 

 rats, as judged by the above description of the microscopic character 

 of their viscera, would seem to be but sparsely charged with plague 

 contagium, and with contagium not necessarily as dangerous to the 

 human subject. 



Plague artificially induced in the Guinea-pig and 

 some other Animals. — We have on several occasions in 

 the preceding pages described the results of the infection 



