560 DISEASES OF THE HORSE. 
if kept at a very low temperature or if left surrounded by carbolic 
acid; but if the nerve matter, which is virulent at first, is exposed 
to the air and is kept from putrefaction by substances which will 
absorb the surrounding moisture, it will gradually lose its virulence 
and become inoffensive in about fifteen days. He has also 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 atmos- 
phere 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 inocu- 
lated 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 the ganglionic cells in 1903 by Negri, 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- 
gators in all parts of the scientific world. An examination of the 
vitality of these bodies will show a striking resemblance to the 
vitality of an emulsion of the virulent tissue. Thus, they have been 
found to be quite resistant to external agencies, such as putrefaction, 
drying, etc., and are about the last portion of the nerve cell to sur- 
vive the advance of decomposition. They are also found in more 
than 96 per cent of the cases of rabies examined, but have not been 
* proved to exist in other diseases. 
Valenti states, as his strongest evidence of the protozoan nature of 
the bodies, that the virus of rabies is neutralized in test tubes by 
quinin, while no other alkaloid has this property. Asa result of the 
work performed in the New York City Board of Health laboratory, 
Park claims that Negri bodies are found in animals before the begin- 
ning of visible symptoms, and evidence is given that they may be 
found early enough to account for the infectiousness of the central 
nervous system. These bodies are now almost universally considered 
as diagnostic of rabies, and in the pathological laboratory of the 
Bureau of Animal Industry their detection in the nerve cells of the 
brain suffices for a diagnosis of rabies without animal inoculations. 
In case these granular bodies are not-found in a suspected animal, 
