130 COLLECTED STUDIES IN IMMUNITY. 



D II represents the last conceivable case. It is assumed that 

 the " completion " of the interbody has resulted in a diminution 

 of the latter's affinity for the bacterial receptor. In this case pri- 

 marily only the uncomplemented interbodies will combine with 

 the bacterial receptors, while the free fluid will contain complemented 

 interbodies. 



In cases C II and D II, therefore, the excess of interbody is not 

 without important results; for whereas in mixtures of equivalent 

 amounts of complement and interbody all the interbodies are com- 

 plemented and so made active, the excess of interbody will exert 

 a deflecting action on the complements in case C II as well as in D II, 

 thus diminishing the end results. 



The conditions shown in B II are apparently those which apply 

 to the hoemolysins, for extensive investigations in this direction by 

 Ehrlich and Morgenroth, concerning which we are permitted to 

 report, have shown that deflection of complement by an excess of 

 interbody is not observed in haemolysis. In this case only the 

 complemented interbodies seem primarily to be anchored by the 

 receptors of the erythrocytes. 



In the bactericidal sera investigated by us, however, the deflec- 

 tion of complement shown in C II and D II is observed, though 

 of course we are as yet unable to say which of the two possible modes 

 is present in any particular case. The same explanation which 

 we have given for the phenomenon observed in vitro must also be 

 held to apply to the experiments on animals, at least so far as the 

 phenomenon above described was observed. It is perfectly obvious 

 that when appropriate affinities of the interbody exist and when 

 there is a marked disproportion between complement and inter- 

 body, a deflection of complement by the excess of interbody can 

 occur in the animal body. 



The phenomenon of deflection as described may perhaps present 

 further points for study. We know that immunization causes an 

 increase only of the interbody and that therefore every immune 

 serum presents a deficiency of complement in comparison to inter- 

 body. Hence it is conceivable in a highly immune animal, i.e. one 

 in which through immunization a great increase of interbody has 

 occurred, that after infection the phenomenon of complement deflec- 

 tion through the excess of immune body could occur. That it actu- 

 ally does occur we conclude from the following statement by R. 

 Pfeiffer: 



