` 1886.] Fhystology. 187 
passed, that from the second to a third rabbit and so on, the dura- 
tion of the period of incubation becomes more and more reduced. 
After the successive inoculation of twenty to twenty-five rabbits, 
the time of incubation is reduced to some eight days, and the 
incubation period remains of this length throughout a further 
series of twenty to twenty-five successive inoculations; then the 
time of incubation is shortened to seven days, which is maintained 
with remarkable regularity throughout a new series of ninety 
inoculations. Pieces of the spinal cords of these rabbits induce 
hydrophobia with constant virulence. When the diseased cord 
is detached from a rabbit under the strictest precautions against 
contamination by impurities, and is suspended in a flask, the air 
of which is kept dry by caustic potash on the bottom, its viru- 
lence gradually disappears and may become wholly lost. The 
virulence fails somewhat more slowly the larger the piece of 
which was maintained dry. As stated above, the virulence of 
each specimen diminished progressively with its exposure. Ster- 
ilized bouillon was inoculated with a small portion of cord which 
had been exposed for such a time that the loss of its virulence was 
certain, and a small syringe full was injected under the skin of a 
og. On each day following a similar operation was performed, 
using, however, at each injection, spinal cord which had been 
exposed for a shorter time and which possessed, therefore, pro- 
gressively increasing virulence. When this procedure had been 
repeated until the dog had received an injection of virus which 
had been exposed to dry air only one or two days, the animal 
was found to be perfectly protected against hydrophobia, and 
might with impunity be inoculated with the strongest virus. 
Fifty dogs were thus made resistant to the disease without a 
single failure, besides which a number were successfully inocu- 
lated after having been bitten by rabid animals. A child which 
ad been lacerated by a mad dog two days before and whose 
wounds had been cauterized with carbolic acid two hours after 
€ injury, was brought to Pasteur for treatment. The method 
pursued was similar to that described, and the final inoculation 
was with virus more virulent than that of ordinary rabies. Three 
months and three weeks after the accident the child was still 
well. Pasteur explains his results by supposing that the products 
formed by the vital activity of the germs of the disease are poison- 
