266 BACTERIOLOGY. 



killed viz., at 55 C. in one hour, at 60 C. in fifteen 

 minutes, at 65 C. in fifteen minutes, at 70 C. in ten 

 minutes, at 80 C. in five minutes, and at 95 C. in one 

 minute. One reason why they appear to withstand in 

 milk high temperatures for a longer time than given in 

 the above figures is, as pointed out by Theobald Smith, 

 that when heated in a test-tube the cream which rises 

 on heating is exposed on its surface to a lower tem- 

 perature than the rest of the milk, and as this contains 

 many bacteria some of them are exposed to less heat 

 than those in the rest of the fluid receive. 



The resisting power of this bacillus against chemi- 

 cal disinfectants is considerable, but not as great as it 

 is apt to appear, for, as in sputum, the bacillus is 

 usually protected by mucus or cell protoplasm from 

 penetration by the germicidal agent. It is not always 

 destroyed by the gastric juice in the stomach, as is 

 shown by successful infection experiments in susceptible 

 animals by feeding them with tubercle bacilli (Baumgar- 

 ten and others). They are destroyed in sputum in six 

 hours or less by the addition of an equal quantity of a 

 3 per cent, solution of carbolic acid, and in about one 

 hour by an equal amount of a 5 per cent, solution. 

 Bichloride of mercury is unsuitable for the disinfection 

 of sputum unless used in very strong solutions (1 : 500). 

 From recent experiments by Yersin upon pure cultures 

 of the bacillus it appears that tubercle bacilli were killed 

 by a 5 per cent, solution of carbolic acid in thirty sec- 

 onds; by 1 per cent, in one minute; absolute alcohol, 

 five minutes; iodoform-ether, 1 per cent., five minutes; 

 mercuric chloride, 1 : 1000 solution, ten minutes. Salt- 

 ing and smoking are said not to destroy the virulence 

 of tuberculous meat (Forster). 



