328 PROTECTIVE INOCULATIONS. 



a solution of bichromate of potash and sulphate of copper, colored 

 with a solution of hrematoxylon, 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 microorganisms in the 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. In a 

 second communication (December llth, 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 



