DISEASES OF UNKNOWN ETIOLOGY 423 



hyperimmunized against hog cholera, infected accidentally 

 with the foot and mouth disease, the serum being used for 

 the immunization of healthy swine. One of the outbreaks 

 in the United States was due to the introduction of the virus 

 with smallpox vaccine from calves infected with the disease. 



RABIES OR HYDROPHOBIA 



This disease is known as hydrophobia in man and rabies 

 or lyssa in animals. The causal organism of the disease is 

 questionable. It has been claimed by a group of investi- 

 gators headed by Negri that certain bodies which may be 

 demonstrated in the larger ganglion cells of the Ammon's 

 horns of the brain are the specific organisms capable of 

 causing the disease. These have been named the Negri 

 bodies. These bodies are so constantly present in the brains 

 of animals having the disease that they are regarded as 

 diagnostic. Whether they are specific protozoa or degenera- 

 tion products of brain cells has not been definitely proved. 



Rabies is a disease primarily of dogs and closely related 

 carnivora, transmissible to a wide variety of animals and to 

 man through direct inoculation. 



The virus enters the body through a wound, usually the 

 bite of a rabid animal. After an incubation period of 

 several weeks the symptoms of the disease are manifested. 

 Apparently this time is required for the causal organism to 

 pass from the site of initial infection to the central nervous 

 system. 



The disease is of particular historic importance as it was 

 the first of the diseases of man in which vaccination proved 

 effective, with the exception of smallpox. The Pasteur 

 treatment is carried out by vaccination with an attenuated 

 virus. Tests made upon experimental rabbits have shown 

 that virus secured from different diseased animals, the so- 

 called " street virus'* is decidedly variable in its ability 

 to produce disease. By passage through a number of 



