172 LOUIS PASTEUR 



inoculated into healthy fowl it would not only do 

 them little harm, but would protect them against 

 the disease in a virulent form. Pasteur had made 

 his great discovery — the attenuated virus. 



The results naturally recalled the celebrated vac- 

 cination for smallpox discovered by Jenner, and 

 Pasteur believed that he had hit upon the explana- 

 tion of the success of that procedure which had 

 hitherto been a complete mystery. Visions of 

 great possibilities in the control of epidemic dis- 

 eases flashed before his mind, and he was filled 

 with enthusiasm over the prospects of further dis- 

 coveries in the fields which were now opened up. 



That germs could be modified, that modified 

 germs were less deadly when injected into animals 

 and that animals so treated became protected 

 against attacks of virulent strains of the same kind 

 of germs was a discovery whose generality he was 

 eager to put to the test. Being occupied more or 

 less with anthrax while he was working with 

 chicken cholera, and being familiar with the 

 method of cultivating the germs of that disease, 

 the next object of attack was, as it were, marked 

 out for him. He set out to attenuate or weaken 

 the germs of anthrax. 



The culture of the anthrax bacillus under con- 



