166 PASTEUR 



form of points almost imperceptible under the 

 most powerful microscopes. It was here that 

 the inventive genius of Pasteur displayed itself. 

 Since he could not cultivate these microbes in 

 appropriate liquids and attenuate them ac- 

 cording to the method that he had used in the 

 case of anthrax and chicken cholera, he con- 

 ceived the idea of cultivating them from rabbit 

 to rabbit, and in this way he obtained a fixed 

 maximum of virulence which reduced the 

 period of inoculation to seven days. But how 

 was the virus to be transformed into vaccine? 

 Pasteur observed that the infected marrows, 

 when brought into contact with dry air, lost 

 their virulence in proportion to the length of 

 time they were exposed, becoming almost harm- 

 less after fifteen days. 



.The attenuated virus having been found by 

 a process which, although hardly scientific, was 

 certain, the next facts to ascertain were : First, 

 whether inoculation with this vaccine virus 

 would render dogs resistant to hydrophobia; 

 and, secondly, whether inoculation would pre- 



