SIDE-CHAIN THEORY OF IMMUNITY. 343 



groups of maximal chemical affinity, which are 

 suited one to the other. The binding groups which 

 reside in the cells and which bind food substances 

 I designate as side-chains or receptors, while I 

 have called those of the molecules of foodstuffs the 

 haptophorous groups. I also assume that proto- 

 plasm is endowed with a large series of such side- 

 chains, which through their chemical constitution 

 are able to bind the different foodstuffs and there- 

 by provide the prerequisite for cellular metabol- 

 ism." 



If the side-chain theory of nutrition is to be- 

 come the side-chain theory of immunity it is nec- 

 essary that it undergo elaboration in order that the 

 formation of antibodies may be adequately ex- 

 plained. If, as Ehrlich assumes, the union of 

 toxin with cell receptors causes the overproduction 

 of the latter as antitoxin, and if this union is an- 

 alagous to that of food substances with similar re- 

 ceptors, one may wonder that antibodies are not 

 formed for our ordinary foods, antibodies which 

 would be discharged from the cells and which 

 would unite with circulating nutritious particles 

 and thereby bring about a condition of starvation. 

 Without entering into the intricacies of this ques- 

 tion, it seems probable that normally a condition 

 of physiologic equilibrium exists between the food 

 substances on the one hand and the cellular activi- 

 ties on the other, so that the union of food with 

 protoplasm constitutes no abnormal stimulus to 

 the ' Leistungslcern" of the cell. When, however, 

 cells are diverted from their normal metabolic 

 function by union with toxins and other "abnormal 

 food substances/' the effect on the cell is de- 



Side-Clinin 

 Theory Ap- 

 plied to 



Immunity. 



