CHAPTER XXXIV. 

 RABIES, VACCINIA AND THE FILTERABLE VIRUSES. 



RABIES is a disease of dogs and wolves, but is communicable to man 

 and domesticated animals. The virus, whatever it may be, resides in 

 the saliva and nervous structures. It is destroyed by a temperature of 

 50 C. In man the period of incubation is usually from three weeks to 

 three months, but may be shorter or may extend over one year. 



Bites about the face and those with marked lacerations are particularly serious. 

 Bites of rabid wolves give about four times as great a mortality as those of dogs. 

 In the dog there are two types of the disease dumb rabies and furious rabies. 



By inoculating rabbits subdurally with an emulsion of the brain or spinal cord 

 of a rabid animal, and successively the medulla of this rabbit subdurally into other 

 rabbits, we finally so increase the virulence of the infection that rabbits die in six days. 

 Beyond this it is impossible to increase the virulence and it is termed "fixed virus." 

 The pathogenic power of this virus is also changed so that it is not apt to cause rabies 

 if injected subcutaneously. To attenuate this virus the spinal cord of the rabbit 

 is removed and is dried over caustic potash at a temperature of 23 C. The cord is 

 divided into segments about i inch in length. Drying for about fifteen days seems 

 to entirely destroy the virus. 



To prepare the material for prophylactic injections a small portion of the cord is 

 emulsified with normal salt solution and injected subcutaneously. The German 

 method is to commence with a cord that has been desiccated only eight days. At 

 first injections are given daily, and it is possible to inject three days' cords by the 

 sixth day. The immunity is "active" and the immunizing agent is a "vaccine." 

 Like vaccine virus the product can be preserved (for probably a month) by the use 

 of glycerine so that it is now possible to send the material for inoculation from the 

 laboratory preparing it. 



The treatment lasts for about twenty days. In the diagnosis of rabies in dogs 

 it is preferable to preserve the animal so that the development of the symptoms 

 may be observed. 



In case the dog has been killed, it may be possible to make a diagno- 

 sis by means of the Negri bodies. These are round or oval bodies from 

 i to 2on in diameter, which may be found in the nerve-cells, especially 

 those of the cotnu ammonis (Hippocampus major). 



These bodies were first described by Negri in 1903. In street rabies large amoe- 

 boid forms from 18 to 23;* may be found, while in the nerve tissues of animals with 

 "fixed" virus only minute forms, 0.5/4 or less, may be detected. The fact that the 



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