BACTERIOLYSIS AND ALLIED PHENOMENA 



175 



heated immune serum destroyed a very large number of the 

 bacteria. When, however, the immune serum is added in larger 

 proportion than this it does harm instead of good: 0-5 c.c. of 



fresh serum completely sterilizes the amount of the culture used, 

 whereas after the addition of i c.c. of immune serum its action 

 is barely noticeable. An excess of amboceptor shields the bacteria 

 from the solvent action of the complements. These test-tube 

 experiments explain the results obtained in vivo, and enable us to 

 form some idea as to the mechanism of the process. 



Neisser and Wechsberg offered the following explanation : They 

 assume that the molecules of complement and amboceptor unite 

 in the mixture before the latter has attached itself to the bacteria. 

 Owing to the excess of amboceptor, there will not be sufficient 

 molecules of complement to go round, and it will follow that a 

 variable proportion of molecules of amboceptor will be uncom- 

 plemented. Unless we suppose that the union of the complement 

 has changed the affinity of the cytophile group of the amboceptor 

 for the bacterium, it will follow that not all the amboceptors which 

 attach themselves to the bacteria will be charged with comple- 

 ment, and therefore able to exert a bacteriolytic or solvent action. 

 To take a concrete case, let us suppose that there are twice as 

 many molecules of amboceptor as of complement. Half the 

 molecules of the former will be complemented, and it will follow 

 that, though all the (appropriate) receptors of the bacterium are 

 occupied by amboceptor, only half of these will have their comple- 

 mentophile groups occupied, and this may not be enough to 

 injure it. 



