172 PRACTICAL METHODS IN IMMUNITY 



add increasing drops of the inactivated i to 100 immune serum. Thus, i drop to 

 No. i tube, 2 drops to No. 2 tube, and so on. After incubating for two hours, we 

 take a pipette and plate out a fraction of a drop in an agar plate. The limit at 

 which bacteriolysis is complete is shown by there being an absence of colonies. 



Beyond or below that point colonies are more or less abundant. The explanation 

 of this phenomenon of deviation or deflection of the complement is that where we 

 have an excess of amboceptors for available receptors on the bacterial cells, only a 

 portion of the amboceptors can attach themselves to their specific bacteria. The 

 free amboceptors, not being able to form a union with the bacterial cell receptors 

 (for which they have a greater affinity), combine with the complement present. 

 Unless the complement be in excess, there will be no free complement left to join 

 on to the amboceptors attached to the bacterial cells, and consequently bacteriolysis 

 does not take place and the plate cultures show an abundance of colonies. 



Stimson has found, in titrating his complement and amboceptor for complement- 

 fixation tests, that keeping his complement content constant and successively increas- 

 ing the amount of amboceptor gives increasing haemolyzing effect up to a certain 

 point, beyond which the further addition of amboceptor causes a lessening of 

 haemolytic power. 



This he regards as due to deviation of complement and in his tests he prefers to 

 keep a fixed amount of amboceptor and adjust his titrations by increasing comple- 

 ment rather than amboceptor. 



FIXATION OR ABSORPTION OF THE COMPLEMENT 



One of the controversies in connection with the nature of the com- 

 plement is that regarding the question of the unity of complements 

 or whether there exist different kinds of complements for different 

 amboceptors (unity and multiplicity of complement). To prove that 

 a single complement will act with varying amboceptors, Bordet and 

 Gengou showed that the same complement would activate both haemo- 

 lytic and bacteriolytic immune bodies. If to a mixture of typhoid 

 bacteria and inactivated typhoid immune serum some guinea-pig serum 

 is added and the mixture allowed to remain at 37C. for two hours, 

 and then sensitized red cells be added and the mixture again placed 

 in the incubator for two hours, no haemolysis will be found to have 

 occurred, because the bacteria have absorbed all the guinea-pig com- 

 plement through the intervening typhoid amboceptors, and there is no 

 complement left to haemolyze the red cells through the specific red 

 blood-cell amboceptors. 



If, instead of immune typhoid serum, the serum of a normal person had been used, 

 there would have been no amboceptors to unite the complement to the bacterial 

 cells. The complement would then be at hand to unite with the sensitized red cells 

 subsequently added and bring about their haemolysis, as shown by the ruby red 

 color of the fluid. 



