ANTIIKAX. 345 



animals. It has been found possible to weaken the patho- 

 genic powers of even the strong cultures by proper laboratory 

 cultivation, and this fact has led to one of the epoch-making 

 discoveries in regard to germ diseases. 



PREVENTIVE INOCULATION. 



One of the most important discoveries made in connection 

 with this disease was made by Pasteur in 1881, and resulted in 

 the use of the so-called anthrax vaccine. After having demon- 

 strated conclusively the causal connection of the bacillus and 

 the disease and its probable means of distribution, Pasteur 

 turned his attention to the discovery of some method of pre- 

 vention. In thinking over the matter there occurred to him 

 the well-known fact that a single attack from some of the 

 infectious diseases, if recovered from, renders the individual 

 immune against a second attack. He asked himself the ques- 

 tion whether this was true of anthrax and, succeeding in find- 

 ing an animal that had recovered from the disease, he inocu- 

 lated it with the anthrax bacillus. The animal was not 

 affected by the inoculation, proving thus that one attack may 

 produce a certain amount of immunity from a second. Pas- 

 teur also knew that, in general, a mild attack of a disease con- 

 veyed immunity as well, and possibly as efficiently, as a severe 

 attack, a mild form of a disease producing immunity from 

 a severe form. Vaccination against small-pox by the virus of 

 cow-pox served him as an example of a mild disease protect- 

 ing the individual from a more severe type. He then argued 

 that if he could contrive to give animals a mild form of an- 

 thrax they would probably be protected from a more severe 

 form. 



To accomplish this end was not a simple task. It would 



be of no use to inoculate an animal with a small quantity of 



the bacilli, for these, by multiplying, would soon become so 



numerous as to produce a severe attack of the disease. It 



29 



