1 68 IMMUNE SERA 



nutritive substances in the fowl's organism is not 

 in use during the passage through the pigeon and 

 may become atrophied, so that on the parasite 

 being transferred back to the fowl, supposing one 

 of the specific constituents of fowls to be neces- 

 sary for its proliferation, it would no more be 

 able to grow. We have, therefore, a loss of cer- 

 tain receptors which are absolutely necessary for 

 nutrition. 



Ehrlich suggests that probably the majority of 

 so-called non-pathogenic micro-organisms, if intro- 

 duced into an animal's body, perish by this mechan- 

 ism. It is not necessary to assume the presence 

 of special 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. They thus fall a prey to the phagocytes 

 which destroy the invaders in a non-specific 

 manner. 



