IMMUNITY 



269 



EHRLICH'S THEORY 



From his studies of the production of antitoxins, agglutinins, lysins and pre- 

 cipitins and their action both in vivo and in vitro Ehrlich evolved a theory of 

 immunity commonly referred to as "Ehrlich's Side-Chain Theory," which may 

 be briefly summarized as follows: 



The digestion of food in the alimentary canal is not an adequate preparation 

 of it for assimilation by various tissue cells, hence each tissue cell of the body 

 must select and draw to itself certain substances in the blood serum and further 

 digest them for its nutrition; and reject other substances in the serum not 

 appropriate to its needs. 



Tissue cells possess numerous side chains, each having an affinity for a 

 particular substance needed by the cell for its nutrition. 



In conformity with a general law of nature when these side chains or receptors 

 are exhausted and when the requirements of the cell increase, a superabundance 

 of new receptors is produced. Receptors produced in excess of the cell's needs 

 are cast off and circulate in the blood serum. Receptors in the blood serum 

 manifest the same specific affinities and unite with the same substances as when 

 attached to cells, precipitating, agglutinating, neutralizing or disintegrating 

 them. This may be illustrated by the following diagrams (Fig. 46.): 



FIG. 46. 



I. Represents a cell with two different kinds of receptors. C, cell; A, recep- 

 tors with affinity for one substance; B, receptors for anothec substance. 



U. Represents the same cell after stimulation producing an increased 

 number of receptors. 



III. Some of the excess receptors cast off by the cell. 



IV. Represents poisonous substance or food with which receptors A would 



unite. 



Appetite, digestion within the stomach and intestines and absorption from 

 these organs is for alimentation; some substances devoid of nutritive properties 

 are not assimilated when taken into the alimentary canal, but pass through it 

 without affecting the body. 



One may possess an appetite or that which is poison and not food; the 

 stomach and intestines may digest and pass into the circulation some noxious 



