IMMUNITY. 



221 



r-f 



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 



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. 



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 



