222 INFECTION AND IMMUNITY. 



posure to the action of trypsin. An agglutinating 

 serum which is dried and kept free from moisture 

 and the action of light retains its power unaltered. 

 Similar to agglutinogen, agglutinin is thought not 

 to be a uniform substance, one portion being sus- 

 ceptible to heat, and another portion resistant; 

 these have been called alpha and beta agglutinins. 



structure of It is convenient to speak of the reaction between 

 agglutinin and agglutinogen, and of the process in 

 the body through which agglutinins are formed, in 

 terms of the side-chain theory. Accordingly, if 

 that constituent of micro-organisms which we have 

 termed agglutinogen is the substance which stimu- 

 lates the tissues to form agglutinin, we must as- 

 sign to it a haptophorous group through which it 

 may unite with the receptors of the tissue cells. 

 This haptophore comes into play again in the union 

 between agglutinogen and agglutinin, which pre- 

 cedes agglutination. There is no reason for as- 

 signing to agglutinogen any other structure than 

 this single haptophore ; it is a passive body, similar 

 to antitoxin, and has no other function than that 

 of uniting either with cell or with agglutinin. 



structure of Agglutinin also must have a haptophorous or 

 bi n( ji n g group, inasmuch as it enters into combina- 

 tion with agglutinogen. In addition to this bind- 

 ing group, experiments have shown that agglutinin 

 possesses a toxic constituent, which is analogous 

 to the toxophorous group of the toxin molecule. 

 In this case, however, it is called a zymotoxic, 

 zymophorous or agglutinophorous group; suppos- 

 e $[y i t nas a ferment-like activity (Fig. 6). The 

 analogy with toxins goes further, in that the 

 zymotoxic group of agglutinin may degenerate or 

 may be destroyed, leaving the haptophorous group 



