548 DISEASES OF THE HORSE. 



^animation, and degeneration in the central nervous system. It is a 

 disease that is most common in the dog, but is transmitted to the 

 horse, either from dogs or from any other animal affected with it. 

 (See also remarks on page 222.) As a disease of the horse it is in- 

 variably the result of the bite of a rabid animal, usually a dog. 



Perhaps no disease in medicine has been the object of more con- 

 troversy than rabies. Certain medical men of prominence have 

 even doubted the existence of the disease. Many medical men have 

 claimed for it a spontaneous origin. The experience, however, of 

 ages has shown that contagion can be proved in the great majority of 

 cases, and, by analogy with other contagious diseases, we may only 

 believe that the development of one case requires the preexistence of 

 a case from which the virus has been transmitted. Pasteur has 

 further added to our knowledge of the disease by showing that a 

 virus capable of cultivation exists in the nervous system, especially 

 in the lower part of the brain (medulla oblongata) and in the ante- 

 rior part of the spinal column. Pasteur has further shown that 

 that portion of the nervous system which contains the virus, the 

 exact nature of which has not yet been demonstrated, will retain it 

 for a very long time if kept at a very low temperature or if left sur- 

 rounded by carbonic acid ; but if the nerve matter, which is virulent 

 at first, is exposed to the air and is kept from putrefaction by sub- 

 stances which will absorb the surrounding moisture, it will gradually 

 lose its virulence and become inoffensive in about fifteen days. He 

 has further shown that the action of a weak virus on an animal will 

 prevent the development of a stronger virus, and from this he has 

 formulated his method of prophylactic treatment. This treatment 

 consists in the successive inoculation of portions of the nerve matter 

 containing the virus from a rabid animal which has been exposed 

 to the atmosphere for thirteen days, ten days, seven days, and four 

 days, until the virulent matter which will produce rabies in any 

 unprotected animal can be inoculated with impunity. A curious 

 result of the experiments of Pasteur is that an animal which has 

 first been inoculated with a virus of full strength can be protected 

 by subsequent inoculations of attenuated virus repeated in doses of 

 increasing strength. 



Innumerable attempts have been made to discover the causative 

 agent, and investigators have announced the finding of many of the 

 lower forms of animal and vegetable life as the pathogenic factor. 

 Among the recently described causes, certain protozoanlike bodies, 

 found in 1903 by Negri in the ganglionic cells, and termed Negri 

 bodies, are of a very suggestive nature. Negri claims that these 

 bodies are not only specific for rabies, but that they are protozoa and 

 the cause of the disease. His work has been corroborated by investi- 



