1 70 Immunity 



should result in marked increase of the complement. As a 

 matter of fact, this does take place, but the increase is so 

 slight that the serum is not practically valuable. 



Therapeutic serums whose practical application is based 

 upon their cytolytic activity must, of necessity, contain 

 both the essential factors involved in cytolysis, and should 

 contain them in such proportions that, regardless of other 

 elements in the blood, they can exercise their combining and 

 dissolving functions. 



We are unable experimentally to accomplish these pre- 

 requisites, therefore are not in the position to accurately 

 apply bacteriolytic serums in practice. 



V. Complement Fixation. In 1901 Bordet, while in- 

 vestigating the nature of the complementary substance, 

 made a discovery that has now become of great importance, 

 that is, the " Bordet-Gengou phenomenon," or, as it is now 

 known, the " fixation of the complement." His method of 

 procedure was as follows: Blood-corpuscles were sensitized 

 with appropriate amboceptors and then treated with freshly 

 drawn normal serum. Hemolysis resulted. If now he added 

 to the mixture some sensitized blood-corpuscles of a different 

 species, they did not hemolyze. Clearly, the complement had 

 been used up in the first hemolysis. 



He next found that if, instead of employing blood-corpuscles 

 for the first test, he used sensitized bacteria i. e., bacteria 

 treated with an immune serum containing the amboceptors 

 appropriate for effecting their solution the complement would 

 similarly be used up, " fixed," so that when he subsequently 

 added sensitized red blood-corpuscles there was no hemo- 

 lysis. 



This reaction was naturally quantitative, the result as de- 

 scribed depending upon the fact that no more complement 

 (normal serum) was used in the original hemolysis or bac- 

 teriolysis than was necessary, and so none left "unfixed" 

 to effect the lysis or solution of the second factor introduced. 



Bordet interpreted his results as indicating that there was 

 only one complementary or solvent substance, and though 

 Khrlich subsequently published what he looked upon as 

 proofs to the contrary, the opinion of Bordet prevails. 



In addition, however, Bordet's experiments have been of 

 practical use. As affording a means of quantitative experi- 

 mentation they have enabled investigators to measure the 

 quantity of complement in normal bloods and in immunized 



