264 INFECTION AND IMMUNITY, 



in the immunized animal ; and this union, it seems 

 necessary to assume, takes place through a binding 

 group. The mere possession of a haptophore, how- 

 ever, does not account for the ferment-like activity 

 of complement. The latter characteristic resides 

 in the so-called zymotoxic group; hence, comple- 

 ment, having a binding and a toxic group, has a 

 structure like that of a toxin. 



Somewhat loosely we have said that the inactiv- 

 ity of a serum which has been heated to 56 C. 

 depends on destruction of the complement. This 

 is not strictly true, however, for such treatment 

 destroys only the zymotoxic group, the haptophor- 

 ous constituent remaining uninjured. Comple- 

 ment altered in this respect is called complemen- 

 toid, and it is analogous to toxoid, agglutinoid and 

 precipitoid. Two essential facts go to show that 

 this is the principle change wrought by heating. 

 First, the fact stated above, that immunization 

 with complementoid, causes the formation of 

 anticomplement. Second, complementoid may 

 exceed true complement in its affinity for the 

 amboceptor, and if sensitized cells are treated with 

 a serum containing a mixture of complement and 

 complementoid, the latter may occupy completely 

 the complementophilous haptophores of the ambo- 

 ceptors and thus may block the way for action on 

 the part of complement. This is again the spe- 

 cific inhibition which has been mentioned in con- 

 nection with toxoids, agglutinoids and precipi- 

 toids. This is the Complement oid-Verstopfung 

 (complementoid obstruction) of Ehrlich. 

 Formation The amboceptor, as the characteristic property 

 of Amiocp- Q a bactericidal or of a hemolytic serum, is a spe- 

 cific product of the immunization, whereas the 



