146 PRACTICAL METHODS IN IMMUNITY 



serum, the destruction of the bacteria ceases, and the cultures will again 

 contain myriads of living bacteria. 



To carry out the test, make a series of tubes containing mixtures of bacteria 

 with the same quantity in each of normal serum. Thus, each tube contains 1/2 c.c. 

 of bacterial emulsion and 1/2 c.c. of i-io normal serum. Now inactivate a tube of 

 i -zoo immune serum and to each of the tubes of normal serum and bacterial emulsion 

 add increasing drops of the inactivated i-ioo 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 bac- 

 teriolysis 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 

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

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



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 be allowed to remain at 37 C. for two hours, 

 and then sensitized red cells be added and the mixture again be 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 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 color of the 



