IMMUNITY. 317 



blood-serum of cholera patients for the pur- 

 pose both of curing patients suffering with 

 cholera and of protecting healthy individuals 

 from its attack, but it is not clear what his 

 theory of the proceeding was. Hericourt and 

 Richet in 1888 inoculated dogs with pyaemia- 

 staphylococci, and the dogs developed local 

 abscesses. When the serum of such dogs, after 

 healing was accomplished, was conveyed to 

 rabbits animals which otherwise would have 

 rapidly succumbed to infection with the dis- 

 ease all of the rabbits were found to be pro- 

 tected, whereas the serum of healthy unin- 

 oculated dogs protected the rabbits only in a 

 fraction of the cases. The serum of healthy 

 dogs exerted a certain influence, but the serum 

 of those dogs which had endured the definite 

 affection possessed much more perfectly the 

 power of imparting immunity to the disease. 

 The quantitative difference in this case at 

 least was in favor of the preliminary " specific " 

 immunization. 



Babes and Lepp discovered in 1889 that the 

 serum of dogs immunized against hydropho- 

 bia protected other dogs against the disease. 

 More important was the discovery of Behring 

 and Kitasato in 1890, that the blood and blood- 

 serum of animals that had been immunized 

 against tetanus and diphtheria conferred upon 



