344 COLLECTED STUDIES IX IMMUNITY. 



the antibody belongs to this group as follows: The red blood-cells 

 are treated with a just neutral mixture of haemotoxin and antibody 

 and then centrifuged. If there was a true deflection of the poison, 

 these cells must now behave exactly like fresh blood-cells; above 

 all they must still possess exactly the original binding capacity for 

 the hsemo toxin. 



In contrast to this behavior, the disturbance caused by trans- 

 formation products of the hsemolysin itself manifests itself even 

 in experiments made only with blood-cells and the toxic substance. 

 The experimental series has an irregular course analogous to Shiga's 

 experiments with agglutinins. For example, if increasing amounts 

 of agglutinating serum which has previously been heated are added 

 to dysentery bacilli, one can observe that the test-tubes containing 

 the largest amount of agglutinins show no agglutination; and that 

 agglutination shows itself only in the tubes containing smaller amounts 

 and disappears again with still smaller quantities. 



In order to show that in this case there is no real occupation 

 of the receptors by the proagglutinoid, one tests the behavior of the 

 centrifuged bacteria. These are suspended in salt solution, and 

 again mixed with what is otherwise an effective dose of agglutinin. 

 They are no longer agglutinated because the agglutinin cannot com- 

 bine with the blocked receptors. We do not doubt at all that this 

 phenomenon will also be found in haemagglutinins. 



The conditions are far more complicated with the complex hae- 

 molysins, the possibilities for the inhibitory mechanism being more 

 numerous. It may, therefore, be well to aid our analysis by means 

 of a diagram (see opposite). 



The diagram refers to experiments made with mixtures which 

 do not by themselves dissolve blood-cells, and whose composition 

 must first be accurately determined quantitatively. One next devises 

 a hsemolytic combination in which amboceptor and complement are 

 present in exact equivalence and determines the amount of the anti- 

 body in question which will just inhibit the action of this combina- 

 tion. By means of this exactly balanced mixture experiments by 

 the centrifuge method are made both with the sediments and 

 with the decanted portions as shown in the diagram. 1 



1 This method refers to cases I, III, and IV of the scheme, while case II 

 refers to an experiment made with ordinary complementoid serum obtained by 

 heating. 



