IMMUNITY. 373 



terfering with the usual energetical processes 

 of the body-cells. Viewed in this aspect, the 

 " specific " bodies are as a rule best suited for 

 attaining the desired end, but since their spe- 

 cificity is not due to an ability to effect a neu- 

 tralization of molecule by molecule, other bod- 

 ies also must be able to interfere in the same 

 way and to influence the same " specific " cell 

 territories. Even the passive protective in- 

 oculations are not entirely dependent upon 

 the mere addition of chemical substance to the 

 blood serum, but owe their influence to a 

 stimulus to the cells and a corresponding re- 

 action on the side of the cells, and hence in 

 reality they also are active. 



The distinction between active and passive 

 inoculation is only a quantitative one, and both 

 kinds of immunity result from the action of 

 " specific " stimulating substances upon the 

 body-cells and the reaction of the cells to these 

 stimuli. The " exhaustion hypothesis " first 

 propounded by Klebs and Pasteur, according 

 to which certain substances occurring in the 

 organism of the host and necessary to the life 

 of the micro-parasite are exhausted by the 

 growth of the parasite, thus rendering the host 

 an unsuitable culture medium is untenable. 

 The " retention hypothesis, " put forward by 

 Chauveau, which supposed that metabolic 



