256 THE FILTERABLE VIRUSES 



Hydrophobia. This disease has long been considered to be an 

 infectious one, but the causal parasitic agent has never been dis- 

 covered. It is commonly found in dogs, cats, wolves, rabbits, etc., 

 but other domestic animals, and man may become infected. It is 

 a disease of the central nervous system, highly infectious, always 

 following a bite or other injury in which the skin is broken, and 

 in which lesion the virus may be deposited. Infection may be 

 caused by injecting emulsified infected nerve tissue (brain) into 

 susceptible animals (rabbits or monkeys). The disease is always 

 fatal after it is well established. Well-marked histological lesions 

 of the central nerve tissues, particularly the large ganglia, have 

 been found by Van Gehutchen and Nelis, and Ravenel and Mc- 

 Carthy. If emulsified brain tissue from an animal that has died of 

 hydrophobia is filtered through a "germ-proof " filter the nitrate is 

 capable of setting up the disease in a healthy animal if it is injected 

 into it. By long centrifugation of emulsified infected brain tissue, 

 the supernatant fluid loses its power of reproducing the disease on 

 injection. Virus may also be found in mammary and lacrymal 

 secretions, pancreas, cerebro-spinal fluid and aqueous humor. 



The organism is toxic in character, since filtrates sometimes fail 

 to produce transmissible disease, but emaciation, paralysis, and 

 death are caused by their injection into rabbits, the tissues of 

 which, in turn, are not infectious. 



The unknown organisms are rather resistant to agents that are 

 germicidal. They are destroyed in fifty minutes by a 5 percent 

 carbolic solution, and in three hours by a 1-1,000 corrosive subli- 

 mate solution. Direct sunlight kills them quickly, as do radium 

 emanations. The latter have been used -as curative measure 

 with reputed success. A temperature from 52 to 58C. for one- 

 half hour destroys them, but they resist extreme cold of liquid air 

 (312) for many weeks. Pasteur found that desiccation attenu- 

 ated the virus. Chlorine kills it quickly, while glycerine does not. 

 The virus may be increased in virulence by passing the " street 

 virus" of dogs through a series of rabbits. Here the period of 



