60 EXPERIMENTAL RESEARCHES 



poisons in the body, it suffices to suppose that 

 the bacteria in question do not find the needful 

 means of existence in the body and therefore 

 cannot multiply. This being the case, they 

 cannot for any length of time remain alive in 

 the body, for then the latter's defensive forces, 

 its phagocytes, come into action and destroy 

 the invaders in a non-specific manner. 



In the case of the pathogenic micro-organ- 

 isms it will, however, as a general rule be safer 

 not to attribute too great an importance to 

 atrepsy. But it is evident that micro-organ- 

 isms can only be pathogenic for a certain 

 animal if they find in it possibilities of nutri- 

 tion. Yet, to my mind, quite a number of 

 infections are characterised by the fact that the 

 micro-organism, with the exception of only a 

 few remnants, becomes atreptic. As an exam- 

 ple of such an occurrence I would mention the 

 fine researches of my friend, A. Neisser, who 

 found that monkeys injected subcutaneously or 

 intra-peritoneally with great quantities of syphi- 

 litic virus became neither infected nor im- 

 munised. 



It does not appear possible to assume that in 

 the serum of monkeys, substances should be 

 present which destroy the causative agents of 



