BACILLUS PESTIS 415 



and that the bacilli were present at least three weeks after the last 

 feeding. In the absence of fleas no infection takes place, at least in 

 man. The bite of the infected flea may result in infection, or, since 

 the feces of the flea are usually deposited during feeding, laden with 

 plague bacilli, the irritant flea bite may lead to scratching of the area, 

 resulting in the "rubbing in" of the bacilli deposited with the rat 

 feces. Epidemics of pneumonic plague are spread by droplet infection. 

 Preventive measures include the appropriate care of the patient and 

 measures to reduce the rat population. This is accomplished by careful 

 disposal of all garbage, rat proofing all houses and granaries, and an 

 active campaign against rats by poison, destruction of nests and run- 

 ways, and the creation of rodent-free zones of considerable magnitude 

 around settlements. 



FIG. 60. Influenza bacillus from sputum. X 1200. (Kolle and Hetsch.) 



Bacteriological Diagnosis. Human. The juice of buboes, 1 of lymph 

 glands, of petechise, the blood, the sputum from pneumonic cases, 

 and occasionally the urine contain plague bacilli in large numbers. 

 They may be obtained readily from the spleen, liver, lungs and kidneys 

 of the cadaver. 



Animal. The postmortem appearance of plague-infected rats is 

 very characteristic. 



Microscopical Diagnosis. The presence of Gram-negative ovoid 

 short bacilli in considerable numbers in films prepared from material 

 outlined above is very suggestive, but not conclusive evidence of 

 infection with Bacillus pestis. In man the evidence is stronger than 



1 Buboes which have suppurated frequently do not contain plague bacilli, or plague 

 bacilli in association with extraneous organisms. Even if buboes have not developed, 

 the lymphatic glands usually contain the bacilli. 



