164 BACTERIA 



In animals, plague occurs in rats. It is supposed that some 

 tropical soil bacilli infect rats, and becoming accustomed to the 

 rodent's body, are eventually transmitted to man. The bacilli 

 may be transmitted from rat to rat in India by the rat fleas 

 which also can bite man. The organisms remain in the flea for 

 some time. Rats are also infected from dead rats. In epidemic 

 times the soil becomes infected and persons going barefoot may 

 be infected. 



FIG. 44. B. Pestis in pus of bubo. . (Jackson.) 



Pathogenesis. Highly pathogenic for man. Is the cause of 

 the bubonic or Oriental plague; bacilli gain entrance by way of 

 the skin, causing localized foci of infection from which buboes 

 develop, followed by pest-sepsis and death. The lungs may be 

 the original site of invasion, and plague pneumonia (worst form 

 of the disease) may result. The typical bacilli. can be found in 

 the sputum of the patient thus affected but not in quietly expired 

 air. The mortality from this plague is from 50 percent to 80 

 percent. 



Almost all domestic animals rats, mice, guinea pigs, rabbits 

 and squirrels are susceptible; horses and swine are very suscep- 

 tible; cows and dogs less so. Rats seem to be affected with a 



