SIDE-CHAINS. 341 



Just as the side-chains of the "Leistungskerri" 

 may combine with food particles, so may the side- 

 chains of the benzol ring combine with other 

 groups of atoms and thereby assimilate the latter, 

 so to say, into the ring. To choose a simple exam- 

 ple, the sodium of sodium hydroxid may unite with 

 the side-chain CO OH to form sodium benzoate, 

 the hydrogen of the acid radical being replaced by 

 the sodium, thus : 



o 



i- 



H 

 \ * 



c 



Presumably it is in some such manner as sodium 

 is brought into relationship with the benzol nu- 

 cleus, in the example cited, that the food sub- 

 stances are brought into relationship with the 

 "Leistungskern" of the cell. 



The hypothesis of Ehrlich carries with it the 

 assumption that the side-chains of a cell possess or 

 consist of definite groups of atoms capable of unit- 

 ing chemically with certain other definite groups 

 of atoms in the food particles ; hence both the side- 

 chain and the food substance have combining 

 groups haptophores. The side-chains of the cells 

 Ehrlich now calls receptors, elements which we 

 have already recognized in connection with im- 

 munity. Inasmuch as different foods have differ- 

 ent chemical compositions, it is likely that their 

 binding groups are not identical; and if this be 



