ETIOLOGY 463 



large ganglion cells of the Anunons horn. Negri believed 

 these bodies to be the etiological factor of the disease and clas- 

 sified them among the protozoa. 



He believes the bodies are specific microorganisms which 

 are characteristic of the disease, found only in animals affected 

 with rabies. They appear early in the course of the disease. 

 They occur in larger numbers and are of greater size as the 

 disease progresses. They are most numerous and largest at 

 the time of death. Smears or sections are stained in saturated 

 alcoholic solution of eosin for from 10 to 30 minutes after which 

 they are counter-stained in alkaline methylene blue. No 

 special technique is necessary to demonstrate these bodies. 

 Their constant appearance in cases of rabies forms a basis for a 

 positive opinion and diagnosis and they are affected very little 

 by beginning decomposition of the surrounding nervous tissue. 



Williams and Lowden state concerning the channels of 

 infection that "in whatever way the virus enters the body, so 

 far as we know, there is no development of the organism, or 

 none, to any appreciable extent, until it reaches the central 

 nervous system, and not until after a certain amount of deve- 

 lopment there does it infect the peripheral organs. Before the 

 disease was well studied it was thought that the salivary glands 

 were the chief site of the infection. But it has been shown 

 that these glands are not always infective, and when they are, 

 not until comparatively late in the disease and that when the 

 virus is inoculated into tuem, the animal .seldom comes down 

 with the disease and probably never if the centripetal nerves 

 are cut (Bertarelli). This means that the parasite does not 

 grow in the salivary glands, that it is only carried there inci- 

 dentally by its spread from the central nervous system along 

 the nerve branches. That the organisms escape into the blood 

 and are carried in this way in small numbers is shown by the 

 fact that the blood in large quantities has been found infective 

 (Marie). Principally by the nerve channels, secondarily by 

 the blood and lymph channels, the organisms are carried in 

 small numbers to all parts of the body. With other investiga- 

 tors, we have found the suprarenal cepsules infective." Their 



