NON-SPECIFIC COMPLEMENT FIXATION 421 



tion with various lipoidal and bacterial antigens. The mechanism of this 

 phenomenon is not understood ; it would appear that the complement- 

 absorbing body is in both the serum lipoids and proteins. 1 Heating 

 these sera at 56 C. for half an hour greatly increases their property for 

 non-specific fixation of complement; heating at 62 C. for the same period 

 lessens the tendency. 2 The subject is of great importance in view of 

 the frequency with which complement-fixation studies are conducted 

 with rabbit, dog, and mule sera. 



Quantitative Factors in Complement-fixation Tests. From what 

 has been said it will, therefore, readily be appreciated that complement- 

 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 



1 Jour. Infect. Dis., 1916, 18, 46. 2 Jour. Infect. Dis., 1916, 18, 64. 



