IMMUNITY. 51 



could be obtained, by taking it at the right time, which gave only a 

 mild disease, and afforded subsequent protection. 



At Melun, in 1881, the protective inoculation against anthrax 

 was put to a practical test. Sheep and oxen were inoculated with 

 the mitigated virus, and then with a virulent form ; at the same 

 time other sheep and oxen were inoculated with the virulent form 

 without previous vaccination, as a control experiment. The unpro- 

 tected sheep died without exception ; the unprotected oxen suffered 

 from cedematous swellings at the seat of inoculation, and a rise of 

 temperature ; but all the protected animals remained healthy. 



As a result of these experiments an idea arose that by preventive 

 inoculation with attenuated virus all communicable diseases would 

 in time be eradicated ; but this does not follow, for all communi- 

 cable diseases do not confer immunity after a first attack ; in 

 influenza the very reverse is believed to occur, and erysipelas of the 

 face leads to an increased liability to subsequent attacks. Even 

 with regard to the prevention of anthrax, Pasteur's researches were 

 opposed and criticised. Koch investigated the subject, and came to 

 the conclusion that the process did not admit of practical applica- 

 tion, chieflv on the ground that as immunity lasted only a year, the 

 losses from the vaccination process would be as great or even 

 greater than from the spontaneous disease ; further, there was 

 danger in disseminating a vaccine of the strength required to be 

 effectual. 



Chauveau proved that the attenuation was due to the tempera- 

 ture, and not to the prolonged effect of oxygen. By keeping 

 cultivations at 42 to 43 C. in vacuo, the virulence was found 

 to disappear in twenty-four hours, and by keeping cultivations 

 at a low temperature with free access of air, the virulence was 

 retained. Chauveau considered, therefore, not only that oxygen \\a> 

 not the agent, but that the mitigation was much more easily effected 

 in its absence. In spite of these adverse criticisms, these researches 

 nevertheless confirmed the principle of Pasteur's conclusion, that 

 immunity could be induced by experimental measures, and further 

 showed that he had considerably advanced the methods by which this 

 could be effected. 



Chauveau succeeded also in attenuating the virus by a modifica- 

 tion of Toussaiut's method. Sterilised broth was inoculated with 

 the bacilli, and placed in the incubator at 42 to 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 degree. Thus inoculation with the virus, l^efore 



