230 STUDIES IN IMMUNITY. 



absorb the sensitizer energetically and deprive the fluid of it. This 

 fact was first irrefutably proved by Ehrlich and Morgenroth.* 



The third fact established by us a year ago f is that, in a 

 mixture of fresh normal serum (alexin) and sensitized corpuscles 

 or bacteria (that is, treated with an appropriate heated hemo- 

 lytic or bacteriolytic serum) the alexin that destroys the sensitized 

 cells is absorbed by them and disappears from the fluid. This fixa- 

 tion may be so complete that the fluid completely loses its power 

 to destroy subsequently added sensitized cells. 



These are the principal facts derived from experiments, apart 

 from any theory. We may now attempt to explain the reactions 

 between sensitive cells and active substances in the light of these 

 facts. 



According to Ehrlich and Morgenroth the specific antibody 

 (sensitizer) acts as a real intermediary body (Zwischenkorper, 

 Ambocep tor), a joining link united on the one hand to the corpuscles 

 and on the other to the alexin. In other words, the absorption of 

 the alexin by the sensitized corpuscles is not due to any distinct 

 affinity of the corpuscles for the alexin. The absorption of the 

 alexin is indirect only: the corpuscle is joined to the intermediary 

 substance which unites chemically by its other pole with the alexin. 



Our conception of the phenomenon is quite different. We re- 

 gard the sensitizer as uniting with the corpuscle and so modifying 

 it as to allow a direct absorption of the alexin. The action of the 

 sensitizer on cells would be similar to that of fixing or mordanting 

 agents that give certain substances or, in histological technic, certain 

 cells the power of absorbing dyes that were previously not taken. 

 We know that slight modifications suffice to make cells take stains 

 that normally do not affect them. To be sure, in speaking of mor- 

 danting we do not mean that all the phenomena of dyeing must 

 agree with the phenomena under consideration; we have simply 

 offered a comparison in order to simplify our explanation. The 

 hypothesis we wish to emphasize is that in presence of hemolytic 

 serum the corpuscle itself becomes capable of absorbing alexin 

 directly, owing to its modification by the sensitizer. In other words, 

 we see no reason for considering that the sensitizer itself combines 



* Loc. cit., p. 6. 

 t See p. 186. 



