CHAPTER XIII. 

 THE METHOD OF COMPLEMENT FIXATION. 



Its principle, antituberculin, Ehrlich's side-chain theory, serum diagnosis of syphilis, 

 and diseases caused by animal parasites. 



It has already been demonstrated that neither bacteriolysis 



The Question nor hemolysis can take place without the presence of comple- 



of Multipli- ment. The question therefore arises whether this complement 



city of Com- is the same in both of these reactions or whether normal serum 



plements. possesses different complements. In order to solve this, a 



number of very complicated experiments have been carried 

 out by Ehrlich and Morgenroth, Metschnikoff and Bordet and Gengou. 

 Ehrlich and Morgenroth endeavored to show that not only do the comple- 

 ments of different animals of the same class vary, but that numerous com- 

 plements exist within one individual serum (conception of the multiplicity of 

 complements). Metschnikoff believed that each serum contained at least 

 two complements, the microcytase and the macrocytase, thus enlisting the 

 supporters of a dualistic theory. Bordet and his school, on the other hand, 

 although agreeing with the idea that the complement varies in different 

 animals, deny its multiplicity and contend that any given serum contains 

 but one alexin, or complement the theory of unity of complement. It 

 would be superfluous to cite all the experimental data supporting these 

 opinions, but nevertheless a review of the classical experiment of Bordet and 

 Gengou which corroborated the existence of only one complement, thus 

 offering the fundamental principle for the establishment of the most impor- 

 tant method of serum diagnosis, namely, complement fixation, would not be 

 out of place. 



Bordet and Gengou mixed in a test-tube typhoid bacteria 



The Principles (antigen), inactivated typhoid immune serum (amboceptor) 



of Comple- and normal serum (complement). Union of the bacteria and 



ment Fixation, immune serum first took place followed by absorption of, and 



coalescence with, the bacteriolytic complement contained in the 

 normal serum. As a result, bacteriolysis occurred and the bacteriolytic com- 

 plement was used up during this process. Bordet and Gengou reasoned 

 that if the bacteriolytic and hemolytic complements were identical, then in 

 the above mixture of typhoid bacteria, immune serum and normal serum, 

 the hemolytic as well as bacteriolytic complement should be absent, while 



