14 VACCINE AND SEBUM THEEAPY 



The strictly specific character of such reactions, 

 furthermore — diphtheria antitoxin binding diphtheria 

 toxin, tetanus antitoxin only tetanus toxin, etc. — led 

 him to assume that the chemical affinity between 

 each antibody and its respective antigen depended 

 upon definite atom groups contained in each. 

 Ehrlich discusses the manner of cell nutrition, and 

 advances 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 w^ere made up of central atom 

 groups upon which depended the specialised activities 

 of the cells and a multiplicity of side-chains, by 

 means of which the cell entered into chemical re- 

 lation with food and other substances brought to it 

 by the circulation. 



Just as nutritious substances are thus brought into 

 workable relation with the cell by means of the 

 atom groups corresponding to side-chains, so Ehrlich 

 believes that toxins exert their deleterious efiects only 

 because the cell possesses side-chains by means of 

 which the toxins can be chemically bound. These 

 side-chains he calls ''receptors." These receptors 

 present in the cell and possessing by chance specific 

 affinity for a given toxin are, by their union with 

 toxin, rendered useless for their normal physiological 

 function. By the normal reparative mechanism of 



