IMMUNITY. 339 



establishment of a tolerance of the organism 

 to serpent venom. 



The blood of the hedgehog, according to 

 Phisalix and Bertrand, is poisonous to guinea- 

 pigs. If this blood be heated and its poison- 

 ous qualities destroyed, it is able to protect 

 guinea-pigs against the bite of the common 

 adder. The protection against the poison in 

 this case evidently does not depend upon the 

 action of an anti-substance, nor can it be due 

 to the neutralization of the poison by a specific 

 antidote. 



When immunization is accompanied by the 

 acquisition of a tolerance of poison it is fre- 

 quently the case that no antidote for the 

 specific poison can be discovered in the serum 

 of the protected animal. Emmerich first 

 proved for swine-erysipelas and pneumonia 

 that the active bodies to which the properties 

 of the protective serum are due act not anti- 

 toxically, but bactericidally ; that is, that they 

 kill the specific bacteria. Novy established 

 the same thing for the swine-plague, and R. 

 Pfeiffer has recently discovered that the same 

 fact is true of cholera. 



In the latter case the normal serum of 

 healthy animals may act bactericidally, al- 

 though in a lesser degree than that of animals 

 specifically inoculated. On this ground it 



