

PASTEUR TREATMENT FOR RABIES 27 



Pasteur found that rabies can be transmitted to dogs by injecting them 

 subdurally with the brain substance of rabid animals. This ordinary virus 

 substance is known as Street Virus. 



The incubation period of rabies is very long. It varies from about three 

 weeks to [possibly] some years. By passing the virus through monkeys, 

 the incubation period is considerably increased. After the successive 

 passage through five or six animals, the virus becomes so weakened that 

 infection is almost impossible. Reversely, increase of the virulence may 

 be affected by passing the virus through a successive number of rabbits, 

 as these are very sensitive to the disease. After passage through a large 

 number of such animals, the incubation period is gradually shortened from 

 about three weeks or a little less to a constant period of six or seven days. 

 Further diminution in the period of incubation was impossible and there- 

 fore Pasteur called this " Virus fixe." His first experiments in immuniza- 

 tion were made by passing the weakened monkey virus through rabbits 

 and then treating dogs with the spinal cords of the latter. 



Later on, Pasteur discovered that instead of passing the virus through 

 monkeys, he could diminish its virulence by drying the spinal cords derived 

 from rabid animals, for varying periods of time. In this way he could 

 prepare an entire series of graduated strengths. The material used for 

 this drying was not the street virus, but that obtained by successive pas- 

 sage through rabbits or "virus fixe" which possessed very constant im- 

 munizing and infectious properties. By drying the "virus fixe" over 

 caustic potash at a temperature of 23 to 25 C. for five days, its regular 

 incubation period of 7 days was very much prolonged. Increase in the 

 length of drying caused the entire loss of virulence. 



Pasteur immunized dogs as follows: He began with the injection of a virulent 

 spinal cord which had been dried for thirteen days and every following day injected 

 subcutaneously some fresher spinal cord, i.e. (dried for a lesser period of time), until 

 finally he used virus dried only for one day. The animals thus treated were immune 

 against the bites of rabid dogs as well as subdural, subcutaneous, and intravenous 

 infection with "virus fixe " and street virus. This procedure was strongly recom- 

 mended by Pasteur, who brilliantly contributed the observation, that if an animal 

 was' infected but did not as yet show symptoms, these could be prevented by a similar 

 modus operandi, as above mentioned. 



In man, the inoculation is carried out on the same principle. The 

 fact that the incubation period of hydrophobia is very long, makes the 

 prophylactic inoculations of greater service. Only rarely is this period less 

 than six weeks, usually considerably longer up to 584 days, entirely 

 dependent upon the virulence of the virus and the point of infection. 



