150 ORIENTAL PLAGUE chap. 



mission of plague from rat to rat by means of fleas cannot 

 be on theoretical grounds denied. But the question to 

 which answer is wanted is the extent to which this 

 method of transmission is common, as compared with the 

 more obvious methods previously mentioned in reference 

 to this animal, viz. by cutaneous abrasions or wounds 

 coming in contact with plague -infected matter, by in- 

 gestion, or by way of the respiratory tract. In order to 

 assign to these different modes of transmission their 

 proper r61e it is necessary to bear well in mind — (l) the 

 distribution of B. pestis in an infected animal (rat), and 

 (2) the experimental evidence at present to hand in regard 

 to production of plague in the rat by one or another 

 method. 



In a rat acutely affected with the virulent or human 

 type of plague B. pestis is distributed throughout the 

 body. If an animal has been cutaneously inoculated the 

 nearest lymph glands are crowded with B. pestis ; the 

 blood of the general circulation contains the bacillus in 

 great number ; the spleen is crowded, sometimes literally 

 packed with them ; and in the blood-vessels of the liver, 

 the lungs, and the kidneys B. pestis is abundant. 



In more than fifty per cent of the animals the small 

 intestine is found relaxed and much congested ; and its 

 cavity contains blood -tinged mucus, which under the 

 microscope shows along with blood corpuscles numerous 

 bipolar -stained bacilli. Guinea-pigs injected subcutane- 

 ously with this mucus, and rats inoculated with it cutane- 

 ously, develop in the great majority of instances definite 

 plague. Whenever, in fact, a rat dies of plague and shows 

 the above condition of the small intestine, viz. congestion of 

 the wall and blood within the cavity, the probabilities are 



