THE ^ETIOLOGY OF RABIES. 
215 
try to obtain, if possible, a more rapid method, and one giving 
isolute security to dogs. After almost innumerable experiments, 
obtained a preventive method, practical and prompt, with which 
ifficiently numerous and assured successes have already been 
fiained upon dogs to give me confidence in its general applica- 
lity to all animals and to man himself.” 
This method, as gathered from Pasteur’s communication and 
om his assistants while in the laboratory, rests especially upon 
e following observations: 
In the human being or in animals dead of rabies, the rabic 
rus is present in great abundance and in a pure form in the 
ntral nervous system, and especially in the medulla oblongata 
id the spinal cord. This observation is not wholly original, but 
in confirmation of the experiments made by Possi and Hertwiir, 
tio succeeded in producing rabies in healthy dogs by inoculations 
th portions of nerves obtained from animals dead of rabies, 
isteur found that animals inoculated with portions of the medulla 
spinal cord, and then brought into suspension in a sterilized 
uillon, developed the disease with greater certainty than when 
I ^culated with the saliva of rabid dogs. This is especially true 
the inoculations are made upon the surface of the brain under- 
ath the^dura mater. Nearly all species of animals are susceptible 
the disease; but the virus undergoes certain modifications as 
?ards its virulence and its period of incubation after passage 
rough different species. In the transmission of the virus through 
series of monkeys, the virulence gradually becomes diminished 
d the period of incubation longer. If, on the other hand, the 
'us is passed through a series of rabbits, the virulence is gradu- 
: y increased and the period of incubation becomes shorter. The 
-rage period of incubation of rabies in rabbits which have been 
>culated under the dura mater, after trephining with the spinal 
•d of a dog just dead of the disease, is fifteen days. However 
:he virus is passed successively through a series of rabbits from 
‘ first to the "second, from the second to the third, and so on, 
rays using for the inoculation of the following animal the spinal 
d of the one just dead of the disease, and in each case making 
i inoculations underneath the dura mater in the same manner 
i. 
