216 DISEASES OF UNKNOWN ETIOLOGY 



to spread by contact either directly with the sick or 

 indirectly by objects having been in contact with them. 

 Such objects are called fomites. Bacteria are present 

 in the pustules caused by vaccination and in the 

 eruption of smallpox, but they have been proven to 

 be secondary invaders. 



Rabies or Hydrophobia. This is an acute infectious 

 disease to which nearly all animals are susceptible, 

 characterized by slowly progressive palsies and de- 

 lirium. Hydrophobia means fear of water. Such 

 an emotion does not exist, but animals merely avoid 

 water because they cannot swallow it. The cause of 

 rabies is excreted in the saliva and may be transmitted 

 by the bite of a rabid animal. The virus is innocuous 

 if swallowed. After having entered the body the 

 virus travels to the central nervous system and remains 

 there throughout the whole attack. The spinal cord 

 particularly is involved. The only evidence there is 

 of the actual causative germ is the presence of minute 

 stainable granules in the nerve cells of the brain. 

 These so-called "Negri bodies" are demonstrated by 

 special staining methods. When a dog is suspected 

 he is killed and his brain removed. Bits of it are 

 stained for microscopic examination and other pieces 

 are made into an emulsion, which is injected into the 

 brain of a rabbit. If rabies virus be present this 

 susceptible animal will die within three weeks as a rule. 



Pasteur found a method for protective inoculation 

 treatment against rabies. He found that if the spinal 

 cord of a rabbit suffering from rabies were dried in a 

 vacuum it lost its virulence for other rabbits. If he 

 dried it two weeks nearly all of the virulence was lost, 



