ORIGIN OF COMPLEMENT 75 



such as the spontaneous disappearance of the complementary prop- 

 erties on standing, inactivation at 56 C., absence of a hemolytic 

 effect at C., etc., the proof that complement is in reality a lipoid- 

 albumin product has not yet been furnished. 



Origin of Complement. Regarding the origin of the complement, 

 Buchner and Metschnikoff both thought that it was derived from the 

 leukocytes, but while Buchner looked upon the substance as a secre- 

 tory product of the living cells, Metschnikoff claimed that complement 

 is not only formed when the cell dies, during the process of blood 

 coagulation; and that it does not exist preformed in the circulating 

 blood. An enormous amount of labor has been expended to support 

 this view of Metschnikoff on the one hand, and to disprove it on the 

 other. As a result it may now be regarded as a fairly well estab- 

 lished fact that the normal body fluids contain free complement even 

 when there is no evidence that leukocytic degeneration has taken 

 place. 



The long discussed question, also, whether or not the blood plasma 

 contains free complement, may now be answered in the affirmative. 

 On the other hand, there can be no doubt that bactericidal substances 

 can be extracted directly from the leukocytes. This can be shown 

 in the following manner: An aseptic exudate is produced in ani- 

 mals by the intrapleural injection of aleuronat, when the cellular 

 elements, which are mostly polynuclear leukocytes (Metschnikoff's 

 microphages) are thoroughly washed with saline, repeatedly frozen 

 and thawed and the resultant material allowed to stand, at body 

 temperature. After a while it can then be shown that this extract 

 is quite rich in bactericidal substances and, like the fresh blood serum, 

 loses its action on exposure to higher temperatures. But on com- 

 paring the behavior of such leukocytic extracts with normal bacteri- 

 cidal sera certain points of difference appear, nevertheless, which 

 suggest that the substances which are operative on the two sides 

 may not be identical. 



Apart from the different temperature at which inactivation takes 

 place and the slower action of the leukocytic extracts which, more- 

 over, can progress in the absence of neutral salts (contrary to the 

 bacteriolytic sera), it is especially noteworthy that certain organ- 

 isms, such as the cholera vibrio and the typhoid bacillus, which are 

 very susceptible to the action of bacteriolysins, are hardly affected 

 by leukocytic extracts. The latter, moreover, contain no substances 



