IMMUNITY 213 



haptophorous groups, conceived after the manner of the 

 reactions of organic chemistry ; and this molecular stereo- 

 chemistry explains all vital phenomena : the action of a toxin 

 on the cell, the action of antitoxin on toxin, the production of 

 antitoxins, and immunity in general. 



Finally, since the same combinations and linkages go on in 

 the metabolic changes of all living matter, the conception of 

 side-chains becomes a general theory of nutrition ; so much 

 so that, with all his chemical language and mechanical attitude 

 of thought, Ehrlich arrives at the same formula as Metchnikoff 

 with his " vitalistic," or rather, biological explanation : 

 immunity is a function of nutrition. 



This idea has been Ehrlich's guiding principle in all his 

 scientific work, and it is from it that we have to start in order 

 to arrive at the principal laws of immunity. 



Let us represent the protoplasm molecule as possessing 

 numerous and varied functions, the agents or the bases of 

 which are distinct atomic groups. This molecule consists of a 

 central nucleus (analogous to the nucleus of the aromatic 

 compounds), which maintains its continuous individuality, 

 and of numerous side-chains or receptors which act towards 

 the nucleus as organs of communication or nutrition. The 

 primary food-stuffs and the toxins which circulate in the blood 

 and body-fluids have haptophore groups which are fixed by 

 the cell receptors ; and it is thus that all the modifications 

 of the protoplasm are carried on. 



Take a poison like the tetanus toxin introduced into the 

 body. We know by definite experiments that it is " fixed " 

 by various cells and in particular by the nerve-cells. The 

 toxin molecule is treated by certain definite receptors of the 

 nerve-cell as a food material ; it possesses a haptophore group 

 which hooks on to the receptor, but it possesses also a toxophore 

 group, an atom group which exerts the toxic action ; it is 

 through the haptophore group that the toxophore group is fixed 

 by the cell and acts as a poison. 



If the toxin has been injected in sufficient quantity, 

 numerous cell receptors are occupied, monopolized by the 



