ORIGINAL COMPLEMENT-FIXATION METHOD OF BORDET 395 



because the alexin had been fixed by the pest antigen and antibody. A 

 similar test, conducted with normal serum, hemolyzed in a few minutes 

 because the complement or alexin remained free in the mixture. Even 

 at this early stage Bordet included the important controls on his antigen 

 and serums that are so necessary in all complement-fixation tests. 



The following table gives the original details and results of the first 

 complement-fixation experiment with pest antigens and antipest serum: 



TABLE 12. THE ORIGINAL BORDET-GENGOU COMPLEMENT- 

 FIXATION REACTION 



Mechanism of Complement Fixation. The divergent views of 

 Bordet and Ehrlich on the mechanism of antigen-amboceptor action 

 have been given elsewhere. Bordet believes that the antibody unites 

 directly with the antigen, and serves to sensitize and prepare it for direct 

 miion with the alexin or complement, in a manner similar to that of 

 using a mordant in aiding the penetration of a dye-stuff. In the absence 

 of the homologous and specific antibody (sensitizer), the antigen is 

 incapable of absorbing more than very small amounts of complement or 

 none at all. In the absence of antigen, the sensitizer and complement do 

 not unite, or unite to but a very slight degree. ' ^The important require- 

 ment for complement fixation is, therefore, an antigen that has been 

 sensitized by the antibody, and in this manner has an increased combin- 

 ing affinity for complement. 



According to Ehrlich and Morgenroth, however, the complement does 

 not unite directly with the antigen, but only indirectly through the 

 antibody, which acts as a connecting link or amboceptor between antigen 

 and complement. Antigen alone, or even amboceptor alone, binds the 

 complement only very slightly or not at all. The important require- 

 ment for complement fixation is an amboceptor attached to its homol- 



