IMMUNITY. 22 1 



But the side-chain theory offers an explanation not only of 

 the mechanism of the union of toxin and antitoxin, but also ex- 

 plains the phenomena of agglutination, precipitation and 

 cytolysis. In the union of antitoxin and toxin, as stated above, 

 the process is a simple combining of the toxin with the recep- 

 tor, and there the process ends. Receptors of this kind are 

 called receptors of 

 the first order (Fig. 

 50). But after the 

 union of the agglu- 

 tinins and of the pre- 

 cipitins with their re- 

 ceptors further change 

 takes place. In the 

 one case, clumping; 

 in the other, precipi- 

 tation; and these 

 changes are brought 

 about by a kind of 

 fermentative action. 

 So, in addition to the 

 haptophore group, 

 the receptor must 

 possess a ferment- 

 producing group. It 

 seizes on the red cells 

 or on the bacteria, as 

 the case may be, with the haptophore group, and produces 

 certain changes with its ferment-producing group. The 

 latter is called the zymophore group. Receptors of this kind 

 are called receptors of the second order (Fig. 51). 



With the lysins there is also a change, which takes place after 

 the receptor unites with the bacteria or other cells; so there 

 must be here also a zymophore or zymotoxic group, as it is 



Fig. 51. — Receptors of the second order and 

 of some substance uniting with one of them. — 

 {Journal of the American Medical Association. 

 1905. P. 1113.) 



c. Cell receptor of the second order, d. Tox- 

 ophore or zymophore group of the receptor. 

 e. Haptophore of the receptor. ' /. Food sub- 

 stance or product of bacterial disintegration 

 uniting with the haptophore of the cell receptor. 



