ON SPECIFIC THERAPEUTICS. 23 



The increase of avidity, which forms the 

 basis of the mode of action of the amboceptor, 

 not only governs the phenomena which occur in 

 the organism, but, since it lends itself to test- 

 tube experiments, also opens up a wide field for 

 serum diagnosis. If we remember that the 

 amboceptors, by their union with the sensitive 

 substances cells or dissolved bodies exert 

 such a marked localising influence on the 

 complements, it is evident that in a mixture 

 of an amboceptor and its corresponding antigen, 

 if the presence of the one constituent of the 

 mixture be known, that of the other can be 

 proved by the occurrence of the phenomenon of 

 complement-fixation. 



This method, which was elaborated by Neisser 

 and Sachs on the basis of the work of Bordet, 

 Gengou and Moreschi, for the medico-legal 

 test of the source of blood by " complement 

 deviation," depends solely on the principle of 

 this increase of avidity. And, thanks to the 

 genius of Wassermann, we possess a similar 

 method of sero- diagnosis for some infectious 

 diseases, the cause of which is at present 

 unknown or invisible a method which has 

 yielded valuable results and gives great promise 

 for the future. 



