NON-SPECIFIC COMPLEMENT FIXATION 419 



of hemolysis, i. e., if a small amount of complement is absorbed, hemol- 

 ysis will be correspondingly incomplete, if all complement is absorbed, 

 hemolysis does not occur at all. If, therefore, in any complement-fixa- 

 tion test the antigen is used in an amount that will give this non-specific 

 absorption, even to a slight degree, a grave source of error is introduced. 



As a general rule for all complement-fixation tests, the dose of antigen 

 employed should never be more than one-fourth or one-half of its 

 anticomplementary dose (that amount which of itself is capable of 

 non-specific complement-fixation). 



2. A serum may of itself absorb a small amount of complement, espe- 

 cially if it is old or infected with bacteria. This is known popularly as 

 the anticomplementary action of a serum, and in every complement- 

 fixation test in order to detect this condition a proper control, consisting 

 of the dose of serum used plus complement, hemolysin, and corpuscles 

 is required, the non-specific absorption of complement being determined 

 by the results of hemolysis. 



Moreover, perfectly fresh serums may show this non-specific absorp- 

 tion of complement to a slight degree, especially in the presence of the 

 lipoidal extracts used as " antigens" in the Wassermann reaction. 



Heating a serum to 56 C. for half an hour largely removes this 

 anticomplementary effect of serums, unless they are quite old and in- 

 fected; accordingly, heated serums are used almost exclusively in com- 

 plement-fixation tests. This is usually called inactivation, or the removal 

 of native complement from a serum, but in the majority of instances 

 the complement of a serum generally deteriorates rapidly, and the serum 

 is heated mainly for the purpose of removing its anticomplementary 

 action, i. e., its ability to effect non-specific absorption of complement. 



By referring to the original Bordet experiment, it will be observed 

 that this investigator controlled any non-specific absorption of comple- 

 ment by both the immune and the normal serum in tubes C and D of 

 the series by using the full dose of these serums, with a similar amount of 

 complement, and noting that hemolysis was complete. His controls, 

 E and F, were to determine if the process of inactivation or removal of 

 native complement from the two serums was complete, and the total ab- 

 sence of hemolysis showed that it was. His control on the anticomple- 

 mentary action of the antigen was also included in tube D, for if the 

 emulsion alone had absorbed complement to any degree, hemolysis 

 would have been incomplete. 



Non-specific Complement Fixation by Normal Rabbit, Dog, and Mule 

 Sera. The fresh normal sera of several species of animals may absorb or 



