440 PATHOGENIC BACTERIA. 



for experimental purposes into a plague district, and 

 kept carefully isolated, died spontaneously of the disease, 

 presumably because of insect infection. 



Yersin found that when cultivated for any length of 

 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. Ogata found 

 that the bacillus was instantly killed by 5 per cent, car- 

 bolic acid, and in fifteen minutes by 0.5 per cent, carbolic 

 acid. In o. i per cent, sublimate solution it is killed in 

 five minutes. 



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. 



Abel finds that the blood may yield fallacious results 

 because of the rather variable appearance of the bacilli, 

 which are sometimes long and easily mistaken for other 

 bacteria. He deems the best tests to be the inoculation 

 of broth-cultures and subsequent inoculation into ani- 

 mals, which he advises should have been previously 

 vaccinated against the streptococcus. Plague bacilli 

 persist in the urine a week after convalescence. 



Wilson, of the Hoagland Laboratory, found the thermal 

 death-point of the organism was one or two degrees 

 higher than that of the majority of pathogenic bacteria 

 of the non-sporulating variety, and that, unlike cholera, 



