IMMUNITY. 167 



access of air the virulence was retained. Chauveau 

 considered, therefore, not only that oxygen was 

 not the agent, but that the mitigation was much 

 more easily effected in its' absence. In spite of 

 these adverse criticisms, these researches never- 

 theless confirmed the principle of Pasteur's con- 

 clusion, that immunity could be induced by 

 experimental measures, and further showed that 

 he had considerably advanced the method by 

 which this could be effected, 



Chauveau succeeded also in attenuating the virus 

 by a modification of Toussaint's method. Sterilised 

 broth was inoculated with the bacilli, and placed 

 in the incubator at 42 43 C. After the lapse of 

 twenty hours it was removed to another incubator 

 at 47 C. According to the time of exposure to this 

 increased temperature, the mitigation varied in de- 

 gree. Thus inoculation with the virus, before it was 

 exposed to 47 C., was fatal to guinea-pigs; but 

 after one hour at 47 C. the virulence was diminished, 

 and, though ultimately fatal, life was prolonged ; 

 after two hours' exposure at 47 C. only half the 

 animals died ; and after three hours' exposure they 

 recovered and were rendered refractory to sub- 

 sequent inoculation. 



Attenuation of the virus has also been induced 

 by chemical means. Chamberland and Roux 

 stated that a fresh growth started from a cultiva- 

 tion of bacilli which had been subjected for twenty- 

 nine days to & JQ of carbolic acid was found to 



