228 



INFECTION AND IMMUNITY. 



production 



order, 



plicity may result from infection by a single micro- 

 organism. 



The explanation of the production of aggluti- 

 nins by the body, according to the conception of 

 Ehrlich, is similar to that already given for the 

 production of antitoxins. That is to say, the ag- 

 glutinin molecules are cast-off cell receptors, the 

 overproduction of which has occurred as a result of 

 their union with the agglutinogenic molecules of 

 the bacteria. The antitoxin receptors were rela- 

 tively simple, having no other demonstrable struc- 

 ture than that of the haptophorous groups through 

 which they unite with the corresponding toxin. 

 We have recognized in the agglutinin receptor two 

 groups, a haptophorous and a zymotoxic; conse- 

 quently it must have this same structure when it 

 is still a part of the cell. Ehrlich designates it as 

 a receptor of the second order, which, being de- 

 fined, is a receptor in which a haptophorous and a 

 zymotoxic group exist as integral parts of the 

 molecule (Fig. 6). 



In accordance with the side-chain theory, the 

 ability of an animal to form agglutinins for a cer- 

 tain organism would depend on its possession of re- 

 ceptors of the second order which are able to unite 

 with the agglutinogenic receptors of the bacterium. 

 It is well established that different animals may 

 not form serums with equal agglutinating powers 

 for an organism. The following is a concrete ex- 

 ample: Wassermann immunized rabbits, guinea- 

 pigs and pigeons with a strain of the colon bacil- 

 lus, and tested the three serums with fifteen other 

 strains of the same organism. The serum of the 

 guinea-pigs readily agglutinated the strain which 

 was used for immunization, but scarcely affected 



