BUBONIC PLAGUE. 321 



time upon culture-media, especially agar-agar, the viru- 

 lence was rapidly lost and the bacillus eventually died. 

 On the other hand, when constantly inoculated from 

 animal to animal the virulence of the bacillus is much 

 increased. 



The bacillus probably attenuates readily. Kitasato 

 found that it did not seem able to withstand desicca- 

 tion longer than four days ; and Yersin found that al- 

 though it could be secured from the soil beneath an 

 infected house at a depth of 4-5 c.cm., the virulence 

 of such bacilli was lost. 



Kitasato found that the bacillus was killed by two 

 hours' exposure to 0.5 per cent, carbolic acid, and also 

 by exposure to a temperature of 80 C. 



It seems possible to make a diagnosis of the disease in 

 doubtful cases by examining the blood, but it is admitted 

 that a good deal of bacteriologic practice is necessary for 

 the purpose. 



Kitasato' s experiments have shown that it is possible 

 to bring about immunity to the disease, though nothing 

 definite in the way of experiment has as yet been re- 

 corded. 



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