TOXINS AND ANTITOXINS 213 



affinity between each antibody and its respective antigen depended 

 upon definite atom groups contained in each. 



Ehrlich * had, in 1885, published a treatise in which he discussed 

 the manner of cell-nutrition and advanced the opinion that in order to 

 nourish a cell, the nutritive substance must enter directly into chemical 

 combination with some elements of the cell protoplasm. The great 

 number and variety of chemical substances which act as nutriment led 

 him to believe that the highly complex protoplasmic molecules of 

 cells were made up of a central atom-group (Leistungs-Kern) upon 

 which depended the specialized activities of the cell, and a multi- 

 plicity of side chains (a term borrowed from the chemistry of the 

 benzol group), by means of which the cell entered into chemical relation 

 with food and other substances brought to it by the circulation. If 

 we illustrate graphically by the chemical conception from which the 

 term side chain was borrowed, in salicylic acid, the formula given, the 



OH 



H C C COOH 



I I 

 H C C H 



v 



C 

 H 



benzol ring represents the "Leistungs-Kern/' or radicle, while OOOH 

 and OH are side chains by means of which a variety of other substances 

 may be brought into relation with the "radicle," for instance, as in 

 methyl salicylate. 



OH 



C 

 (^ C0 2 CH 3 



Just as nutritious substances are thus brought into workable re- 

 lation with the cell by means of the atom-groups corresponding to side 

 chains, so Ehrlich believes toxins exert their deleterious action only 

 because the cells possess side chains by means of which the toxin can be 

 chemically bound. These side chains, Ehrlich in his later work calls 

 "receptors." The receptors or side chains present in the cells and 



1 Ehrlich, " Das Sauerstoffbediirfniss des Organismus," Berlin, 1885. 



