RABIES- VACCINE 



491 



and at the same time witli blood serum, utaken from a horse which has 

 been highly immunized to the anthrax organism. This simultaneous 

 method seems to give very good results. 



Rabies Vaccine. Pasteur observed that the virulence of the 

 virus of this disease was Jess in animals that had been dead for some 

 time than in those just killed, and by experiment he found that when 

 the nervous system of an infected rabbit was dried in a sterile atmos- 

 phere, its virulence attenuated in proportion to the length of time it 

 was dried. A method of attenuating the virulence was suggested to 

 Pasteur and the idea of using it as a protective vaccination soon fol- 

 lowed. 



It is necessary to have for the purpose of vaccination a virus of 

 known or standard virulence. This is prepared from the so-called 

 " street virus," which is usually taken from the brain of a rabid dog. 

 An emulsion is prepared from this material and injected into a rab- 

 bit. As soon as this animal dies, its spinal cord is removed, a similar 

 emulsion made from a small piece of it, and a second rabbit inocu- 

 lated and so on through a series of from 21 — 30 rabbits or until a 

 standard virulence is attained and the virus is said to be "fixed." 

 This " fixed virus " has a much higher degree of virulence than the 

 " street virus " taken from a rabid ^og and its virulence does not vary, 

 always killing rabbits on the sixth or seventh day. 



