MECHANISM OF THE ACTION OF ANTIAMBOCEPTORS. 569 



rate the sensitized blood-cells by centrifuge and replace the serum 

 fluid with the corresponding amount of normal serum (in our cases 

 0.003 cc.). The active substance contained in normal serum is 

 thermostable at 56 C. ; but is destroyed by heating for half an hour 

 to 100 C. The following experiment may serve as an illustration: 



The blood-cells which have been sensitized with 0.003 cc. serum 

 and then separated by centrifuge are treated with a considerable 

 excess (0.5 cc.) of the antiserum. This amount corresponds to that 

 quantity which by itself is just able to overcome the antilytic action. 

 To this mixture are added decreasing amounts of normal rabbit serum 

 which has been heated to 56 C. and to 100 C. After allowing the 

 mixture to stand for half an hour the blood-cells are centrifuged 

 off and suspended in salt solution to which 0.1 cc. guinea-pig serum 

 (complement) is added. 



The result is shown in the following table: 



TABLE II. 



This shows us what a tremendous effect the presence or absence 

 of a small amount of normal serum can exercise. This of course 

 at once explains the difference which manifests itself between the 

 "curative" and the "protective" experiments. In the latter, it will 

 be recalled, the amboceptor and antiamboceptor are first mixed. 

 All of the normal serum constituents, therefore, come into action; 

 whereas in the "curative" experiment these are removed when the 

 blood-cells are centrifuged. 



How are we to conceive the mechanism of this action? Phe- 

 nomena in which an excess of a certain substance produces a 

 change in the character of the reaction are frequently due to the 



