142 Immunity 



formed by this meddlesome medication, the state of the infected 

 animal would be worse than before, because it would now be pre- 

 paring that which by neutralizing the combining affinities of its 

 own immune bodies, would prevent them from combining with the 

 elements to be destroyed and so activating the complements. 



No satisfactory method of experimentally increasing the comple- 

 ment has been devised. If, as Metchnikoff supposes, the comple- 

 ment is microcytase derived from disintegrated leukocytes, aseptic 

 suppurations with active phagolysis 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 pro- 

 portions that, regardless of other elements in the blood, they can 

 exercise their combining and dissolving functions. 



We are unable experimentally to accomplish these prerequisites, 

 therefore are not in the position to accurately apply bacteriolytic 

 serums in practice. 



COMPLEMENT FIXATION 



In 1901 Bordet and Gengou* while investigating 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." The method of 

 procedure was as follows: Blood-corpuscles were sensitized with. 

 appropriate amboceptors and then treated with freshly drawn nor- 

 mal 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. 



They next found that if, instead of employing blood-corpuscles for 

 the first test, they used sensitized bacteria- — i.e., bacteria treated with 

 an immune serum containing the amboceptors appropriate for effect- 

 ing their solution — the complement would similarly be used up, 

 "fixed," so that when they subsequently added sensitized red blood- 

 corpuscles there was no hemolysis. 



This reaction was naturally quantitative, the result as described 

 depending upon the fact that no more complement (normal serum) 

 was used in the original hemolysis or bacteriolysis than was necessary 

 and so none left "unfixed" to effect the lysis or solution of the second , 

 factor introduced. 



They interpreted the results as indicating that there was only 

 one complementary or solvent substance, aiid though Ehrlich sub- 

 sequently published what he looked upon as proofs to the contrary, 

 the opinion of Bordet and Gengou prevails. 



* Ann. de I'lnst. Pasteur, igoi, xv, 290. 



