164 IMMUNOLOGY 



Fixation of Complement by Products op Lysis. — Liefmann and 

 Cohn (1910) showed that during hemolysis there are liberated 

 products which render complement inactive. A number of workers 

 have considered that complement functions as an enzyme and is 

 bound by the products of lysis rather than by the antigen-antibody 

 complex. 



Hill and Parker's Physicochemical Interpretation. — Hill, 

 Parker and McKinstry (1925) give a physicochemical interpreta- 

 tion to a simple equation which they believe explains all the 

 phenomena of hemolysis by complement. In their paper they 

 draw the following interesting conclusions: That complement is 

 a catalyst. It enters into and combines with the cell under the in- 

 fluence of amboceptor. That the latter (amboceptor) contains a 

 ferment which can bring about the release of hemoglobin. Comple- 

 ment acts as a catalyst for this reaction. They conclude that com- 

 plement is fixed by some other fraction of the firmly bound 

 amboceptor and that the quantity of this complement fixing sub- 

 stance does not change during hemolysis. This hypothesis is in- 

 teresting since it is based upon an equation which fits not only 

 their own experimental results but also tliosc of Thiele and Emble- 

 ton, and certain conce])ts advanced l)y Nolf in 1900. Undoubtedly 

 there are many secondary factors introduced when the antigen 

 undergoes visible physical and cliemical cliange such as occurs with 

 Micro.spira comvut or with red cells, which ai'c not present in re- 

 actions of complement with other sensitized bacteria or sensitized 

 inert particles. 



Action of Complement Depends on Concentration. — While it 

 is obviously difficult to be certain of the exact mechanisms involved, 

 there is no difference of opinion over certain observed facts about 

 complement. Thiele and Embleton find that whereas amboceptor 

 unites with antigen regardless of the amboceptor concentration 

 per cubic centimeter, complement action depends upon the exist- 

 ence of a certain minimum concentration of complement per cubic 

 centimeter of the solution. In other words, there might be enough 

 complement in a test tube to hemolyze 50 or more units of red cells, 

 l)Ut unless its concentration per cubic centimeter is adequate no 

 liemolysis will result. Others have shown that while antigen and 

 antibody unite readily at 0° C, complement and sensitized antigen 

 do not, although they do unite at temperatures slightly above zero. 



