398 PHENOMENON OF COMPLEMENT FIXATION 



fixation tests are largely quantitative. Equally fallacious results may 

 be obtained by using too large or too small amounts of the various 

 ingredients. 



While it is possible to use too large quantities of antigen, so that 

 non-specific absorption of complement occurs, leading to false positive 

 reactions, it is also possible to use an amount so small that any specific 

 absorption of complement by antigen and antibody cannot readily be 

 detected. 



The same is true, but to a much less extent, of the immune serum, 

 for while too large amounts of serum may lead to non-specific fixation of 

 complement, surprisingly small amounts may give well-marked specific 

 fixation, this factor depending, of course, upon the quantity of anti- 

 bodies contained in the serum. 



Of even greater importance are the quantity of complement em- 

 ployed and the proper adjustment of the hemolytic system, composed of 

 complement, hemolysin, and corpuscles. 



Too large an amount of complement may furnish sufficient to sat- 

 isfy the amboceptors of an immune serum united with the antigen, 

 with enough free complement left over to produce partial or complete 

 hemolysis when corpuscles and hemolysin are subsequently added. In 

 this manner specific complement fixation would be overlooked and a 

 false negative reaction secured. 



It is also possible to use too small an amount of complement, with 

 relatively large doses of serum and antigen, so that the complement 

 becomes unduly susceptible to non-specific fixation and consequently 

 false positive reactions may be secured. 



It has previously been explained that an excess of hemolysin may 

 offset any slight deficiency in the amount of complement. For instance, 

 if a small amount of complement is specifically fixed by an antigen and 

 its amboceptor, the addition of too large an amount of hemolysin may 

 result in complete hemolysis of the corpuscle, and thus overshadow the 

 slight but specific fixation of complement. 



On the other hand, hemolysis cannot be complete if the dose of 

 amboceptor is too small. With a given dose of corpuscles and comple- 

 ment a certain amount of hemolysin is necessary to produce hemolysis, 

 this dose being determined by a process of titration, as described in a 

 previous chapter. If less than this dose is used, but the amounts of 

 corpuscles and complement remain the same, hemolysis will be corres- 

 pondingly incomplete and lead to false positive reactions. 



A very important feature of all complement-fixation tests will be 



