110 
Pasteur and his Work, 
remain longer in contact with the air it became enfeebled,, 
and attenuated cultures could thus be obtained ; these inocu- 
lated in other rabbits were found to prevent the action of 
the strong virus. Though both aerobic and anaerobic, the air 
destroyed its potency very quickly ; but kept from the air, it 
retained its deadly character for months. It is much to be 
regretted that Pasteur has not stated whether he tried dogs 
with this microbe ; as its discovery, it must be acknowledged, 
did not advance the question as to the exact cause of rabies. 
The incubation of rabies is so uncertain, and sometimes so 
protracted, when produced in the ordinary way, that Pasteur 
became tired of waiting for months for the results of his inocu- 
lations, and therefore sought a more certain and rapid means 
of developing it. At length he could make it appear by intro- 
ducing portions of the brain and spinal cord of dead rabid 
animals beneath the skin of dogs and rabbits, and this nervous 
matter could be kept in a state of purity for a long time ; 
whereas rabific saliva was always impure, and lost its potency 
in twenty-four hours. 
A happy thought induced Pasteur to place this pure nerve- 
virus on the surface of the brain of a dog, by trephining its 
skull while it was under the influence of chloroform, and it 
became rabid in a few days. Other dogs were treated in the 
same way, and nearly all yielded to the malady in less than 
twenty days. This showed that in the nerve substance the 
poison of rabies exists in its most concentrated form, and espe- 
cially in the brain and upper part of the spinal cord (medulla 
oblongata) — the microbe of the disease evidently flourishing 
there most luxuriantly ; though the virus is also localised in 
certain salivary glands and mucous surfaces ; all of which 
peculiarities may account for differences in symptoms in cases 
of hydrophobia. It was ascertained that the disease could be 
developed in an animal by passing infected brain-matter inta 
its blood, through a vein, almost as quickly as by trephining. 
For a number of years, in this country and on the Continent, 
by means of the microscope, extremely minute round bodies- 
have been noticed in and around the upper part of the spinal 
cord and brain of people and animals dead from the disease ; 
these were also observed in Pasteur's laboratory, and it is not at 
all improbable that they are the germs of rabies. 
When the virus was passed through a certain series of 
monkeys, it gradually lost its power, until it was so enfeebled 
that dogs inoculated with it did not suffer from rabies, but 
were, on the contrary, rendered insusceptible to rabific inocu- 
lation. By such means Pasteur succeeded in rendering some 
sixteen out of every twenty dogs he inoculated refractory to rabies. 
