THEORIES OF IMMUNITY. 



with great rapidity — and did not hesitate to 

 conclude that this bactericidal property was re- 

 sponsible for the immunity of the animal to the 

 disease. 



To generalize this fact, Behring and Nissen 

 (Zeit. f. Hyg., 1890, T. Yin., p. 41) undertook 

 a long series of experiments. They showed that 

 in animals well immunized against certain bac- 

 teria (notably "V". Metchnikovii) the blood serum 

 acquired a strong specific bactericidal property, 

 but they also showed at the same time that the 

 blood of animals, even well immunized in other 

 diseases, was very frequently incapable of de- 

 stroying the bacteria. Therefore, the bactericidal 

 property did not appear to be a general charac- 

 teristic and was of limited importance ; and such 

 facts led Behring to abandon the idea that the 

 bactericidal property was an active factor of a 

 general nature, and essential in the production 

 of immunity. 



Buchner confirmed Nuttall's assertion that 

 the bactericidal property disappeared at 55° C. ; 

 demonstrated the part that the salts play in 

 the exercise of the bactericidal action; and 



22 



