THEORIES OF IMMUNITY 147 



Ehrlich asserts that a cell has two important functions: The first is 

 the special physiologic function, as that of a nerve-cell to conduct; of a 

 gland-cell, to secrete, etc. The second function is that of nutrition, 

 and presides over the processes of waste and repair. Furthermore, 

 each of the molecules composing the complex cell is believed to possess 

 these two functions, i. e., one is concerned with the special function of 

 the molecule, and the other, the more important functional portion, is 

 concerned in the nourishment of the molecule. 



The second portion, or that concerned with nutrition, is of more 

 importance in relation to the problems of immunity. Ehrlich con- 

 ceives this as consisting of a special executive center or main portion 

 ("Leistenkern"), in connection with which there are nutritive side- 

 chains, receptors, or haptines ("Leitenketter"), which "seize," or rather 

 enter into chemical combination with, suitable food atoms, which is 

 followed by a sort of digestive or absorptive process, whereby the food 

 material is incorporated in the molecule. 



The function of " seizing" molecules of food from the surrounding 

 tissues implies a selective action or chemical affinity between food 

 atoms and the portion of a cell or side-arm for which it has a chemical 

 affinity, for we cannot conceive that all atoms that circulate in the blood 

 and lymph are suitable for all cells at all times. 



The food molecule in the fluid surrounding the cell is conceived as s 

 possessing a special or haptophore portion for union with the side-arm 

 of a cell molecule, and when brought into relation with one of the side- 

 arms or receptors of the cell molecule, the two are " anchored, " or unite, 

 just as a key fits a lock. The second stage involves a process that may 

 be compared to digestion, by which the food material is prepared and 

 absorbed, in whole or in part, into the molecule of protoplasm. 



These processes, therefore, are conceived as being chemical rather 

 than physical, and our diagrammatic representations of them have no 

 necessary or actual morphologic basis. One is quite likely to regard the 

 main central portion as the nucleus of a cell, and the side-arms as small 

 morphologic projections resembling the prickles of certain epidermal 

 cells. These processes are concerned with each molecule of a .cell, the 

 main portion, or " Leistungskern, " being conceived as diffusing through 

 the nutritive part of the molecule, and the side-arm receptors, or "Lei- 

 tenketter," as numerous atoms or groups of atoms, each of which has 

 a chemical affinity for some particular food-substance circulating in the 

 body-fluids, and necessary for the life of the molecule in question. 



Later this theory was amplified by Ehrlich to explain the action of 





