THEORIES OF IMMUNITY. 



of small non-fatal closes of the pathogenic agent. 

 Looking at the action of the first of these, we 

 see that the cells must be robbed of affinities 

 needed in the ordinary metabolism, by the fact 

 of the attachment of toxine molecules to these 

 affinities or :<r side-chains." (Ritchie, I. c.) The 

 use of the term " side-chain " is unfortunate, for 

 in chemistry it can only be employed in relation 

 to molecules of which the exact composition is 

 known, and this is not the case with any of the 

 toxines; furthermore, it should be employed only 

 in connection with molecules in which the K ben- 

 zine ring " appears, and of course there is no 

 thought of its presence in these toxine molecules. 



Xow, in accordance with general biological 

 law, that protoplasm tends to repair injuries if 

 not too great, — and furthermore, that this re- 

 pair, if it occurs, occurs in excess, — it may 

 be supposed that, when the interference with the 

 cell metabolism is not too great, the tendency 

 is to repair the loss of the haptophorous cell- 

 groups, — which if not replaced would result in 

 the death of the cell; that this replacing goes on 

 to excess, — and that when this occurs the ex- 



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