462 Chapter XV 



It is to Pasteur that science and humanity owe the invention 

 of this method. Aided by his collaborators, especially by Roux, he 

 established in the first place a whole series of important facts on the 

 subject of the rabic virus and of experimental rabies. He then set 

 himself to elaborate a practical method capable of preventing the 

 manifestation of the disease in dogs inoculated with rabic virus and 

 in men bitten by mad animals. He succeeded in solving this problem 

 in 1885. 



Pasteur's antirabic vaccines are prepared from the spinal cords 

 of rabbits that have died of experimental rabies as the result of 

 the inoculation of the virus bearing the name of "fixed virus." 

 Prepared in the laboratory, this virus presents the characteristic 

 feature that when inoculated under the dura mater of rabbits it sets 

 up in them the first rabic manifestations after an incubation period 

 of six or seven days. The disease soon assumes the typical paralytic 

 form which lasts several days. Whilst the period of incubation 

 presents only very limited variation, the time of death is subject to 

 much greater variation, especially according to the season of the year. 

 Sometimes the rabbits will die on the eighth day after the inoculation 

 of the virus : but death may be delayed one or two days, rarely 

 more. 



It is necessary to wait for the natural death of the mad rabbits 

 before the spinal cord is extracted, and not to kill them before this 

 term, for it is only during the final moments of life that the rabic 

 virus is abundant and is distributed uniformly through the whole 

 substance of the organ. After removal from the vertebral canal the 

 cord is suspended in glass vessels containing solid potassium hydrate 

 at the bottom. A whole series of cords so prepared are then kept in a 

 dark chamber heated to 23 C. or thereabouts. The progressive desic- 

 cation which the cords undergo under these conditions diminishes their . 

 virulence. At the end of several days of this treatment the desiccated 

 cord, instead of producing rabies in 67 days in rabbits inoculated 

 under the dura mater by trepanning, induces it after longer periods 

 of incubation. Finally, the cords do not produce even the slightest 

 symptoms of the disease. 



The fundamental basis of the Pasteurian method consists in the 



fact that the desiccated cord, inoculated as an emulsion below the 



skin of animals, produces in them a complete and permanent 



[485] immunity against inoculation of the most powerful rabic virus 



beneath the dura mater. This experiment, frequently repeated on 



