210 LOUIS PASTEUR 



tory Hansen was studying the influence of different 

 strains of yeast upon the flavor of beers and per- 

 fecting methods of obtaining these strains in pure 

 cultures. 



Returning to France Pasteur plunged again into 

 his studies upon hydrophobia. He had perfected a 

 means of preventive treatment against this disease. 

 Could the treatment be made to cure the disease 

 after it had already been introduced by the bite 

 of a rabid animal? The great value of Pasteur's 

 discovery thus far lay more in its promise than its 

 actual utility. With most diseases preventive 

 inoculation after infection with virulent microbes 

 would probably be of little avail, as there would 

 hardly be time for the former to establish immunity 

 before the virulent, unmodified organisms would 

 gain the ascendancy. In any case it is a race be- 

 tween immunization and the development of infec- 

 tion. In hydrophobia, however, one circumstance 

 favors the immunizing process in this race, and 

 that is the slow incubation period of the disease. 

 It is believed now that the virus of rabies enters 

 the central nervous system along the course of the 

 nerves. This accounts in part for the length as 

 well as the variability of its period of incubation. 

 There is a further advantage in hydrophobia be- 



