THEORIES OF IMMUNITY. 



that the toxine is not neutralized by these free 

 antitoxine units before it gets a chance to reach 

 the cells where its function will be to excite the 

 production of more antitoxine units? Even after 

 it gets to the cells, why is it not taken out of 

 them by the stronger affinities of the haptopho- 

 rous groups existing in the blood-stream, as is 

 known to be the case in ordinary diphtheria 

 immunity ? As a matter of fact the toxine is not 

 destroyed in this way, and upon injection it 

 does go on increasing the activity of the cells 

 in throwing off fresh haptophorous atom-groups, 

 and this is a difficulty that is not easy to explain 

 away. This objection does not arise from the 

 physiological point of view, for the first irritation 

 of the cells is a continuous one and does not 

 require the supposition of the existence of free 

 antitoxine molecules in the blood stream. 



The only possible explanation in accordance 

 with Ehrlich's theory is that the affinities in the 

 tissue cell are a little stronger for the toxine 

 than are the affinities in the antitoxine; so that 

 when the combination of toxine and antitoxine 

 reaches the tissue cell, as it must in circulating 



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