390 RABIES 
the brain. It seems to be necessary to lacerate the nerves in order to 
cause infection. This has been proven by inoculating an animal in 
one of the legs with virulent material. After a suitable time, but 
before the symptoms of rabies appear, the virus will be found, on 
-killing the animal, in the nerves of the limb, and even in the part of 
the spinal cord into which the nerve enters, while the upper part of 
the cord and the brain are still uninfected. This explains why the 
earliest symptoms, both in man and animals, such as itching, tingling, 
numbness and other nervous sensations, often, if not always, appear in 
the part of the body which received the virus. Inoculation into the 
large nerve of the leg is almost as certain to produce the disease, as 
inoculation directly into the sub-dural space. In the case of a bite 
about the face and head the route along the nerve to the central 
nervous system is much shorter. While the nerves seem to form the 
main route by which the virus travels, the circulation may at times 
assist, especially in small animals. Nicholl finds that the virus passes 
from the point of infection to the brain exclusively through the nerves. 
He also finds that it is rapidly destroyed in the blood. 
Nocard and Roux, also Rabieaux and Guinard showed that the 
saliva was virulent two days before symptoms appeared. Williams 
and Lowden found “bodies” in the cells before symptoms developed. 
Noguchi has succeeded in keeping the virus of rabies alive on arti- 
ficial media. Further reports on its cultivation are awaited with 
interest. 
Period of incubation. The period of incubation is quite variable 
depending on the site and character of the wound, which is almost 
always a bite, the amount of virus introduced and its virulence. In 
general it may be said for all animals that the period of incubation 
seldom exceeds sixty days, although in man and in some larger ani- 
mals, it sometimes, though very rarely, reaches a year. A few cases of 
a longer period have been reported. The average period as given by 
Ravenel is as follows: 
In man, 40 days; in dogs, 21 to 40 days; in horses, 28 to 56 days; 
in cattle, 14 to 80 days; in cats, 14 to 28 days; in pigs, 14 to 21 days; 
in goats and sheep, 21 to 28 days; in birds, 14 to 40 days. 
In rabbits inoculated subdurally with the brain from rabid animals, 
Moore found the period of incubation to vary from 12 to 62 days and 
the duration of the disease to range from a few hours to three days. 
Westbrook reports a period of incubation in rabbits to extend in one 
case over a hundred days. In the disease as it is naturally con- 
