364 STUDIES IN IMMUNITY. 



that the sensitizer combines with the alexin, has been suggested by 

 Ehrlich and Morgenroth. According to these authors the sensi- 

 tizer molecule has, in addition to the atom group that binds it to 

 the cell receptor (cytophilic group), a second distinct group (com- 

 plementophilic) that unites with the alexin. This explanation, which 

 regards the sensitizer as a bond of union between corpuscles and 

 alexin, suggests two corollaries.* 



In the first place the corpuscle has no direct participation in 

 alexin absorption, but simply takes hold of the sensitizer and then 

 ceases to function. It is, then, the sensitizer that comes into play 

 in alexin absorption by means of its own affinities. And further, 

 on Ehrlich and Morgenroth 's thesis, alexin absorption is a purely 

 chemical reaction due to affinities between atoms or groups of 

 atoms. The complex receptor-sensitizer-alexin may be regarded 

 as a single large molecule, the nucleus of which is the sensitizer and 

 the side chains of which are the receptor and the alexin. 



The alexin, then, would unite with a new and definite chemical 

 complex, and its absorption is not comparable with phenomena of 

 adhesion (the fixation of a toxin by a precipitate, for example) nor 

 with the various dyeing phenomena, in which cases the molecules 

 of the substance to be stained attract the molecules of the dye 

 without intervention of atomic affinities. Nor is it comparable 

 to the common facts observed in the precipitation, agglutination 

 and coagulation of colloidal substances, nor, in short, to the many 

 phenomena due to molecular adhesion. 



According to the second explanation, proposed several years ago 

 by one of the authors of the present article, the sensitizer does not 

 of itself combine with the alexin. It unites with the corpuscles and 

 forms a complex which has the new property of uniting with the 

 alexin and of removing it from the surrounding fluid ; in other terms, 

 neither the proper substance of the corpuscle nor the sensitizer by 

 itself has any perceptible affinity for the alexin. Such an affinity 

 becomes evident only when the proper substance in the corpuscle 

 has become modified (sensitized) as a result of union with the 

 sensitizer and so changed into an alexin-attracting complex. 



According to this hypothesis, there is no question of a comple- 



* In accordance with this conception Ehrlich and Morgenroth have given the 

 name of amboceptor to the sensitizer. 



