164 BACTERIOLOQY. 



successfully attained in the following manner: 

 Cultivations of the microbe, in chicken-broth, were 

 allowed to remain with a lapse of several months 

 between the carrying on of successive cultivations 

 in fresh media. The new generations which were 

 then obtained were found to have diminished in 

 virulence, and ultimately a virus was obtained 

 which produced only a slight disorder; on re- 

 covery the animal was found to be proof against 

 inoculation with virulent matter. The explanation 

 given by Pasteur of this change was, that prolonged 

 contact with the oxygen of the air was the influence 

 which diminished the virulence, and he endeavoured 

 to prove this by showing that if broth were in- 

 oculated in tubes which could be sealed up, so 

 that only a small quantity of air was accessible 

 to the microbe, the virulence of the cultures was 

 retained. 



Toussaint investigated the possibility of attenuat- 

 ing the virus of anthrax. Sheep injected with 

 3 ccm. of defibrinated blood, containing anthrax 

 bacilli, which had been exposed to 55 C. for ten 

 minutes, recovered, and were afterwards insuscep- 

 tible. Pasteur subsequently argued that this 

 method did not admit of practical application ; 

 difficulties would arise in dealing with infective 

 blood in quantity, and artificial cultivations started 

 from this blood could not be relied . upon, as 

 they proved sometimes as virulent as ever. 



Pasteur endeavoured to apply the same method 



