200 INFECTION AND IMMUNITY. 



Multiplicity other substances which penetrate the cells differ 



of Receptors. .',-,. , ., ... i i T ,1 



in their chemical nature, it is probable that there 

 .are various receptors for the various types of sub- 

 stances. The binding, however, is but a prelimi- 

 nary step to profound changes which the substance 

 may next undergo, through the action of other, 

 more vital, cell constituents. That is to say, the 

 receptor is but a link to bring the substance into 

 relationship with the vital activities of the cell, 

 which Ehrlich supposes may reside in a hypotheti- 

 cal "Leistungskern" (action center or nucleus). 

 In view of this conception one readily understands 

 the propriety of considering the receptor as a side- 

 chain of the "Leistungskern" just as the chemist 

 speaks of the various groups which may be at- 

 tached to the benzol ring, or benzol nucleus, as 

 side-chains (See Chapter XIX). 

 Action of In preceding pages it has been emphasized that 



Toxins. F . n 7i , , 



a toxin, in order that it may injure a cell, must 

 enter into chemical combination with its constitu- 

 ents, and it is a fundamental tenet of the Ehrlich 

 theory that this union is one which takes place 

 between the toxin and a cell receptor (side-chain). 

 The cell receptor, then, either is a haptophore or 

 possesses a haptophore as a part of its complex. 



As the physiologic demands are probably re- 

 sponsible for the character of the various recep- 

 tors, it is not likely that special receptors are 

 created when some unusual substance, as a bac- 

 terial toxin, is introduced into the body. Conse- 

 quently, when toxin unites with a cell, it probably 

 occupies receptors which, under normal circum- 

 stances, are employed in some physiologic process. 



If some inert, non-toxic substance should com- 

 bine extensively with cells, a corresponding num- 



