49 



when the virus has been introduced in the ordinary 

 way. The treatment of persons bitten by rabid 

 animals by inoculation with attenuated virus has 

 now been on its trial a considerable time, and a 

 large experience gained. Judgment, it must be 

 stated, still stands in suspense ; but it must also 

 be said that the results obtained tell decidedly in 

 favour of the view advanced. 



The other method by which it has been recently 

 experimentally found that the virulence of bacilli 

 can be weakened is by transmission through an 

 animal of a different nature from that in which the 

 disease naturally occurs. This, in reality, repre- 

 sents the principle at the foundation of the system 

 of vaccination, discovered by Jenner at the close 

 of the last century. It may now be regarded as 

 an accepted conclusion that vaccine-lymph is the 

 virus of small-pox, modified by transmission 

 through the cow. Jenner's discovery consisted 

 in showing that the result of vaccination with 

 the lymph of cow-pox affords as much protection 

 against small-pox as an attack of small-pox itself 



This was the fact he educed, but the knowledge 



D 



