CHRONIC INFECTIOUS DISEASES 95 



but only used a single vaccination. However, the 

 results were no better than those of Behring's 

 methods, and the same objections applied. 



Recently Calmette, of the Pasteur Institute, "has 

 evolved a method of vaccination, the vaccine being 

 prepared from attenuated bovine tubercle bacilli. 

 Calmette demonstrated that if the bovine tubercle 

 bacillus was grown for several generations on a 

 glycerinated media, containing ox-bile, an attenuated 

 type of the bacillus could be produced that was 

 avirulent for the ox. Moreover, not only would the 

 animals withstand a large intravenous dose of these 

 bacilli without any lesions of tuberculosis ensuing, 

 but in the case of cattle, after a period of thirty days, 

 there w^as sufficient immunity established to with- 

 stand intravenous test inoculations with living virulent 

 tubercle bacilli. According to experiments conducted 

 by Calmette with this method, animals which had 

 been vaccinated yearly and were exposed to natural 

 infection continuously for nearly three years, at the 

 end of this time were perfectly free from tuberculosis, 

 whereas control animals had all become affected. 

 Calmette draws the following conclusions from his 

 method of vaccination : 



1. That the avirulent strain of tubercle bacillus 

 behaves as a true vaccine in that, when inoculated 

 intravenously into cattle in suitable doses, it confers 

 a definite immunity, not only against experimental 

 inoculation, but also in the face of natural infection 

 by close cohabitation in infected buildings. 



