466 RABIES 



spinal cord, then through the spinal cord to the brain. This 

 has been proven by inoculating an animal in one of the legs 

 with virulent material. After a suitable time, but before the 

 symptoms of rabies appear, the virus will be found, on killing 

 the animal, in the nerves of the limb, and even in the part of 

 the spinal cord into which the nerve enters, while the upper 

 part of the cord and the brain are still uninfected. This ex- 

 plains the fact why the earliest symptoms, both in man and 

 animals, such as itching, tingling, numbness and other nerv- 

 ous sensations, often appear in the part of the body which re- 

 ceived the virus. In the case of a bite about the face and 

 head the route along the nerve to the central nervous system 

 is much shorter. While the nerves seem to form the main 

 route by which the virus travels, the circulation may at times 

 assist, especially in small animals. Inoculation into the large 

 nerve of the leg is almost as certain to produce the disease, as 

 inoculation directly into the sub-dural space, while injection 

 beneath the skin of the leg is not so sure. NichoU finds that 

 the virus passes from the point of infection to the brain ex- 

 clusively through the nerves. He also finds that it is rapidly 

 destroyed in the blood. 



Resistance of the virus. The action of the virus is de- 

 stroyed by drying and by the action of light. In dry air, pro- 

 tected from light and putrefaction, the virulence of the spinal 

 cord of rabbits is destroyed in fourteen to fifteen days. When 

 spread in thin layers it is entirely destroyed by drying in from 

 four to five days. Sunlight destroys it in about forty hours. 

 The loss of virulence by drying is gradual but quite regular, 

 which fact was taken advantage of by Pasteur in the prepara- 

 tion of his vaccine. The virus may be preserved in neutral 

 glycerin at ordinary temperature for a long time. Roux found 

 that after four weeks in glycerin at 30° C, the virus in a rabid 

 brain had the same power as when perfectly fresh. The writer 

 has found that rabbits inoculated with rabid brains that had 

 been kept in glycerin from three to four weeks did not develop 

 the disease as quickly as those that were inoculated with the 

 freshly removed brain. 



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