RELATIONS OF SENSITIZERS TO ALEXIN. 365 



mentophilic group in the sensitizer fitted to take hold of alexin with- 

 out intervention of the corpuscle; the corpuscle itself takes part 

 in the fixation inasmuch as it is one of the constituent members 

 of the absorbing complex.* 



It is to be noted that this second point of view, in accordance 

 with which the sensitizer has no complementophilic group, is 

 much less compatible with the idea that alexin fixation is a true 

 chemical reaction, implying the formation of a new well-defined 

 compound. 



Unless we suppose that the union of the sensitizer with the cor- 

 puscle receptor is more than a simple attachment, and unless we 

 admit that this union modifies the affected molecules very pro- 

 foundly by causing a new distribution of their atoms, it is difficult 

 to see how this combination can give rise to atom groups avid of 

 alexin when no trace of them is present in either of the two bodies 

 that take part in the reaction. 



This latter conception, however, harmonizes with the idea that 

 the alexin is taken out and absorbed by a process of molecular 

 adhesion rather than by a true chemical reaction. 



We have simply to consider the substance of the corpuscle uniting 

 with the sensitizer as so modified in its properties of adhesion as 

 to form a complex capable of sticking to alexin, as calcium fluoride 

 and other inert chemical precipitates in fine colloidal suspension 

 remove the fibrinogen from plasma. 



Do we not find analogous if not identical instances in the change 



* Ehrlich and Morgenroth, to be sure, have subsequently modified their original 

 theory, at least as regards certain sensitizers or alexins and certain corpuscles. 

 They admit that in certain instances the sensitizer shows no affinity for alexin 

 until it is combined with the cell. It is naturally difficult to discuss or appraise 

 the value of a theory that changes so markedly from year to year. 



To state that the sensitizer combines with the alexin only after union with the 

 corpuscles is practically to adopt Bordet's conception, according to which neither 

 one of the constituents alone is able to fix alexin. Such a statement, moreover, 

 renounces the theory that was so definitely stated at first, namely, that the alexin 

 unites with the sensitizer even when no corpuscles are present. 



If the intervention of the corpuscles is admittedly necessary, the two theories 

 really differ only in logic subtleties. 



It is only fair to add that although Ehrlich and Morgenroth admit that the 

 sensitizer in certain instances can combine only after cell union, they state that in 

 other cases the opposite condition occurs, namely, that the union of the alexin 

 with the sensitizer increases the affinity of the latter for the corpuscle. 



