IMMUNITY. 309 



lation with the specific poisons effects no im- 

 munization. 



It was next proved by various series of ex- 

 periments that completely attenuated bacteria 

 can not as a matter of fact any longer form the 

 " specific " poison. Following out this clue 

 the attempt was made to deprive virulent cul- 

 tures of their poison. The bacterial poisons 

 have, as mentioned on p. 124, the character of 

 active proteid bodies, and in a moist condition 

 they are very sensitive to high temperatures. 

 If the fluids containing the poisons be warmed 

 to about 55-65 they become for the most part 

 inactive and lose their poisonous qualities. 

 As Hueppe has discovered for chicken cholera 

 and Asiatic cholera, Brieger and C. Frankel 

 for diphtheria, F. and G. Klemperer for pneu- 

 monia infection in rabbits, Brieger, Kitasato 

 and Wassermann for cholera, diphtheria, 

 typhoid fever and swine-erysipelas, immunity 

 can be obtained by the use of cultures devoid 

 of poison. The explanation of this kind of 

 immunity is that the bacteria are prevented 

 from growing and forming their poisons in the 

 body ; they are destroyed just as saprophytes 

 are, and the organism of man or of the lower 

 animals is in consequence not subjected to a 

 contest with the bacterial toxins. 



We are still in the dark as to the nature of 



