328 PROTECTIVE INOCULATIONS. 
a solution of bichromate of potash and sulphate of copper, colored 
with a solution of hematoxylon, and decolorized in a solution of fer- 
rocyanide of potash and borax. 
The writer (1887) has made similar preparations, carefully follow- 
ing the method as described by Fol, but was not able to demonstrate 
the presence of microdrganisms inthe numerous sections made. Nor 
have the observations of Fol been confirmed by the researches of other 
bacteriologists who have given their attention to the subject since the 
publication of his paper. 
Pasteur first announced his success in reproducing rabies in sus- 
ceptible animals by inoculations of material “from the medulla oblon- 
gata, the frontal lobes of the cerebral hemispheres, and the cerebro- 
spinal fluid” in a communication to the Academy of Sciences made on 
May 30th, 1881. At the same time he reported his success in the 
discovery of “a method for considerably shortening the period of in- 
cubation in rabies, and also of reproducing the disease with certainty.” 
This was by inoculations made after trephining, upon the surface of 
the brain with material obtained from the brain of a rabid animal. 
Dogs inoculated in this way developed rabies in the course of two 
weeks, and died before the end of the third week—sometimes of furi- 
ous rabies and sometimes of the paralytic form of the disease. Ina 
second communication (December 11th, 1882) Pasteur reports his 
success in communicating the disease by the intravenous injection of 
virus from the central nervous system; also the experimental demon- 
stration of the fact that all forms of rabies may be produced by the 
same virus; also that all portions of the spinal cord of rabid animals 
are virulent, as well as all parts of the brain; also that an animal 
(dog) which had recovered from a mild attack after inoculation proved 
to be subsequently immune, and that “this observation constitutes a 
first step toward the discovery of the prophylaxis of rabies.” On 
February 25th, 1884, many important facts are stated which had been 
developed during the continuous study of the disease, and among 
others the fact that by passing the virus through a series of animals 
of the same species a fixed degree of virulence is established for each 
susceptible species, as shown by a definite and uniform period of in- 
cubation. By this method a virus had been obtained which produced 
rabies in rabbits in seven or eight days, and another which caused 
the development of the disease in guinea-pigs in five or six days after 
inoculation. In a subsequent communication (May 19th, 1884) evi- 
dence is given to show that by successive inoculations in monkeys the 
period of incubation is prolonged, and that the attenuated virus ob- 
tained from a monkey, after several successive inoculations in this 
