102 ESSAYS ON BACTERIOLOGY. 



sixty to seventy generations in several tliousand per- 

 sons, and subsequently proved its efficiency by re- 

 peated inoculations with genuine variola humana. 

 (Whittaker.) Similar experiments were made by 

 Badcock and Senfft. The committees of Lyons (1865) 

 and Turin (1874) opposed these conclusions, but they 

 failed to explain the facts. The whole subject has re- 

 cently been gone over by an English experimenter, 

 who shows how these committees • were misled, and 

 claims to have finally settled the matter. 



We have doubtless something still to learn about 

 the methods of securing vaccine matter by the iaocu- 

 lation of animals with human variola. Perhaps the 

 best results will only be got by using other animals 

 as well as the cow; perhaps we shall have to wait for 

 the discovery of the smallpox germ and the more ex- 

 act experiments which would follow. In the mean- 

 time we must admit the strength of the evidence that 

 cowpox is a modification of smallpox, and that vac- 

 cination is simply variolation in mild and modified 

 form; that it is inoculation stripped of its virulence 

 and dangers. 



Vaccination, in the light of modern knowledge, 

 takes its proper place, falling naturally and easily un- 

 der the sway of those principles which rule in the field 

 of pathology in which it belongs, 



What are some of these principles revealed Ijy a 

 stiidy of that great group of diseases, one attack of 

 which affords immunity? 



