322 BACTERIOLOGY. 



cells, which, however, can continue for a long 

 time to produce the antitoxin. " Passive " im- 

 munity differs in the respect that these " anti- 

 substances " are introduced into the body all 

 cut and dried, as it were. In the latter case 

 the animal treated with serum experiences the 

 benefit of the antidote without on its side bear- 

 ing any of the burden of preparation, while the 

 animal alone that affords the protective serum 

 assumes actively the dangerous responsibility 

 of forming the antidote. In passive immuni- 

 zation the cells of the secondarily protected ani- 

 mal contribute nothing to the acquisition of 

 immunity, and consequently the antidote in- 

 corporated in its body remains like a foreign 

 proteid ; the cells eliminate this strange proteid 

 as quickly as possible. It is f6r this reason 

 that passive immunity is not lasting. 



As Behring's conception has grown in favor, 

 Ferran's experiments upon cholera have been 

 unwittingly taken up again ; immunity 

 -against cholera has been brought about by 

 the use of the serum of cholera patients. G. 

 Klemperer, Lazarus and Metschnikoff found 

 that this serum, varying it is true in an extra- 

 ordinary way, and often not having any effect at 

 all, usually protected guinea-pigs against an in- 

 fection of cholera bacteria which otherwise 

 would have been fatal (protection was often im- 



