BACTERICIDAL ACTION OF NORMAL SERUM 207 



exhausted with B. dysenteric (Flexner) ; the addition of artificial 

 immune-body restored the bactericidal action. 



These results, which are of considerable importance, are 

 at first sight somewhat puzzling. In the light of what has 

 been stated in the previous section regarding the absorption 

 of bactericidal complement by means of heterologous 

 organisms, however, they seem capable of ready explana- 

 tion. It has been shown that a quantity of heterologous 

 organisms, insufficient to affect haemolytic complement, 

 may produce a distinct fall in the bactericidal action, and 

 this has been explained on the supposition that there is a 

 certain moiety of complement that has a great affinity for 

 bacteria in general, and is most actively bactericidal. We 

 do not mean, however, by this that the bactericidal com- 

 plement is quite distinct from the haemolytic. As a matter 

 of fact, if we use a sufficient quantity of dead organisms, 

 we can absorb the haemolytic complement also. We would 

 rather suppose that the complement molecules present all 

 degrees of combining affinity for, and bactericidal action on, 

 a given bacterium, and that those of greatest activity are 

 first absorbed by bacteria in general. Thus when a certain 

 amount of staphylococcus emulsion has acted on a given 

 quantity of normal serum and reduced its bactericidal 

 action for the V. Metchnikovi, the serum still contains any 

 natural immune-bodies originally present for V. Metchnikovi t 

 and it also contains complement. Bactericidal action, how- 

 ever, does not occur, the amount of the residual complement 

 brought into combination with the organisms, directly or in- 

 directly, being insufficient to kill them. The addition of the 

 artificial immune-body, however, is the means of bringing 

 so much weakly acting complement into combination that 

 death of the organisms results. According to this view 

 bactericidal action by the normal serum may differ from 

 the bactericidal action produced by a partially exhausted 

 serum with the aid of an artificial immune-body. In the 



