from an Agricultural and Veterinary Point of View. Ill 
But remarkable and important though this result might be 
considered, he became impatient at having to wait for months 
before he could assure himself that such animals were really 
rendered proof. He therefore set about to find a method by 
which he could produce viruses of different degrees of strength, 
so that he might obtain more certain, more prompt, and more 
practical results. 
This he at last effected by inoculating a rabbit on the brain 
with a portion of the spinal marrow of a rabid dog — this caused 
the disease to appear in about fifteen days. The virus was 
passed on to a second rabbit in the same way, and from this 
through a number — twenty to twenty-five — when the interval 
of latency was reduced to seven days. This happened with the 
greatest regularity in the experiments ; and though the inocu- 
lations from rabbit to rabbit were carried up to ninety, the 
incubation period could not be reduced much below seven 
days. It may be mentioned that the experiments were carried 
on for more than three years without interruption, and without 
having recourse to any other virus than that of the successively 
infected rabbits. 
Consequently, nothing was easier than to have constantly on. 
hand a supply of rabific virus, perfectly pure, and always of the 
same quality or potency ; and this was the practical feature of 
this long and laborious inquiry into the method of inoculation. 
The spinal cord of these rabbits was equally virulent throughout 
its whole extent, and if slices from it were removed, with all 
precautions to maintain their purity and freedom from putre- 
factive germs, and suspended in dry air in flasks (air dried by 
placing fragments of caustic potass at the bottom of the vessels), 
their virulence slowly disappeared until it vanished altogether 
— the rate of disappearance depending upon the thickness of 
the slice, each spinal cord being cut up into fourteen or fifteen 
pieces. Temperature also influenced its disappearance ; as the 
lower this was, so the longer was the virulence maintained. If 
kept in carbonic acid gas, in a humid condition, air being 
excluded and no foreign microbes admitted, the pieces of nerve- 
tissue would remain potent for at least several months. These 
results constitute the scientific feature of the method. 
When it was desired to render a dog refractory to rabies in 
a relatively brief period, a fragment of fresh rabific spinal cord 
from a rabbit dead seven days after inoculation, was suspended 
every day in a series of flasks, the air in which was dried in 
the manner above mentioned. Every day also the dog was 
inoculated beneath the skin with a morsel of this dried spinal 
cord mixed up in a little sterilised broth — commencing with 
the oldest fragment, to make sure that it was not too virulent ; 
