430 RABIES AND ITS CONTROL 



Pasteur (1822-1895). About 1882, Louis Pasteur, a French 

 scientist, realizing that Jenner and others had successfully immu- 

 nized persons by vaccination, decided to apply the same principle 

 to rabies. He had learned several things about the disease : 

 (1) that the virus of rabies was contained in the saliva of mad 

 animals; (2) that it was communicated through bites, and that 

 the period of incubation varied from a few days to several 

 months. He thought that there must be some way of prevent- 

 ing the development of the disease during this long period of 

 incubation. 



Pasteur had examined certain microorganisms in the saliva of a 

 child that had died of rabies. He thought these were the causative 

 organisms. AVlien he injected them in animals, however, they 

 failed to produce rabies. Pasteur inoculated rabbits with saliva 

 from rabid dogs. Hydrophobia took months to develop and some- 

 times did not develop at all. Then he introduced blood from 

 rabid dogs into rabbits and again was unsuccessful. Pasteur sus- 

 pected the disease was in the nervous system and believed that 

 explained the long period of incubation. He took particles of the 

 brain of an animal that had died of hydrophobia and injected them 

 into a number of animals. They all developed and died of hydro- 

 phobia. Evidently, the particles of the brain were more potent 

 or virulent than the saliva in causing rabies. Pasteur was unable 

 to use his usual method of investigating disease. He could not 

 isolate the germ and cultivate it in an artificial medium, because 

 he could not detect the germ. 



Next, he suspended in a sterilized vial a fragment of the brain 

 of a rabbit that had died of hydrophobia. As the fragment grad- 

 ually became dry, its virulence or strength decreased until, at the 

 end of fourteen days, it proved to be harmless when crushed, mixed 

 with pure water, and injected under the skin of some dogs. The 

 next day the dogs were inoculated with brain which had dried for 

 thirteen days. The inoculations were continued, using fragments 



