IMMUNITY. 299 



recovery from the disease, but trie method 

 always protected many individuals and the 

 protection lasted for a long time. 



As far back as 1839 Thiele proved that the 

 supposedly peculiar and independent disease 

 of cow-pox was nothing other than true human 

 small-pox which had been so weakened by 

 passing through the organism of the cow that 

 it behaved in human inoculations not like 

 human small-pox, but like cow-pox. Ceely in 

 1841 produced cow-pox in cows by inoculation 

 with human small-pox. A decade later Bol- 

 linger and Stamm first accurately established 

 the fact that there is no separate disease of cow- 

 pox (a statement that must, to be sure, be cor- 

 rected in so far as that vesicular eruptions 

 sometimes occur on the cow's udder which rep- 

 resent a peculiar disease of bacterial origin, 

 similar to the cow-pox, but not conferring pro- 

 tection against small-pox). Stamm in his cita- 

 tion of one case drew attention to the possibil- 

 ity that cow-pox, in being carried over to man, 

 might again become malignant and indeed 

 even like the original small-pox. The very 

 practice of vaccination might keep small-pox 

 alive in the land and did not tend to extinguish 

 it, since the human race could not cope natur- 

 ally with the disease as it could with the plague 

 and leprosy. Since Stamm became eventually 



