CONSTITUTION OF IMMUNE-BODY 19 



phenomenon is the fact that when a mixture of immune- 

 body and complement brings about a bactericidal action, 

 this may be annulled by increasing the amount of immune- 

 body. According to the above theory, it is supposed that 

 in such a case free immune-body has as much affinity for 

 complement as immune-body combined with bacteria has. 

 Accordingly, when immune-body is present in excess, many 

 of the molecules of immune-body taken up by the bacteria 

 will have no complement attached to them, and thus 

 bactericidal action will not result; whereas, when the 

 amount of immune-body corresponds to that of complement, 

 each molecule of immune-body combining with a bacterium 

 will bring with it a molecule of complement, and thus a 

 greater bactericidal effect results. This, however, is only 

 a theoretical explanation of the phenomenon, and facts 

 have been brought forward which suggest that it is not 

 the correct one ; especially the fact observed by Buxton, 

 namely, that if a particular mixture of complement and excess 

 of immune-body has no bactericidal effect, such effect may 

 be produced on diluting the mixture, a result which appears 

 quite unintelligible according to the above explanation. 



Ehrlich l states in support of his view, that an immune-body 

 acts best in association with the complement of the animal 

 from which the immune-body has been obtained. He cites 

 the interesting result of Wechsberg, that a heated immune- 

 serum for the v. Metchnikovi when obtained from the rabbit 

 is activated by rabbit's complement, and not by pigeon's ; 

 whereas a corresponding immune-body got from the pigeon 

 is activated by pigeon's but not by rabbit's complement. 

 This, however, might well be the case according to the other 

 theory as to the constitution of immune-body, for if an 

 immune-body is a sensitizer it is only natural that it should 

 be adapted to act well in association with the complement 



1 Ehrlich, Festschrift zum sechzigsten Geburtstage von Robert Koch, 1903, 

 p. 509. 



c2 



