MODE OF ACTION OF CYTOLYTIC SERA. 229 



I. DOES THE ALEXIN UNITE WITH THE SENSITIZING SUBSTANCE? 



The first of the three facts mentioned concerns normal sera par- 

 ticularly. In many instances when a certain amount of normal 

 serum from one species is added to the red blood corpuscles of 

 another species only slight hemolysis occurs. It is particularly 

 true that a large number of corpuscles remain intact if the con- 

 tact is brief. If we then separate these corpuscles by centrifugaliza- 

 tion, and wash them so as to remove the normal serum, we find on 

 adding a sensitizer (that is, a heated serum active against the cor- 

 puscles in question) that no hemolysis occurs. This experiment 

 was first performed by Ehrlich and Morgenroth.* It proves that 

 non-sensitized corpuscles mixed with normal serum do not absorb 

 the alexin, for we know that if the alexin is present the addition 

 of an appropriate sensitizer will hemolyze the corpuscles. This 

 fact, that unsensitized corpuscles do not fix the alexin of normal 

 serum, is applicable only to those corpuscles that have remained 

 intact, but bears no relation to the few corpuscles that have been 

 destroyed. There are certain normal sera that have great hemo- 

 lytic activity for certain species of corpuscles. For example^ 

 hen serum destroys rabbit corpuscles energetically.! When these 

 corpuscles are added to hen serum they absorb alexin very dis- 

 tinctly, as is shown by the fact that fresh rabbit corpuscles added 

 to such a hemolyzed mixture remain intact. J 



We may conclude from these two experiments that, when mixed 

 with normal serum, corpuscles that remain intact do not affect 

 the alexin, whereas corpuscles that are destroyed absorb a certain 

 amount. 



The two other facts about the specific hemolytic sera, obtained 

 by injecting animals with defibrinated blood, are the following: 



When a hemolytic serum, previously heated to 55 degrees, is 

 mixed with the corpuscles affected by that serum, these corpuscles 



* See Collected Studies on Immunity. Ehrlich-Bolduan, John Wiley and Sons, 

 p. 1. 



t See article, p. 134. 



J They remain intact even if heated hen serum is also added to the mixture, 

 which proves that it is indeed the alexin that has been absorbed. The objection 

 indeed might be raised that the first corpuscles destroyed have not absorbed much 

 alexin, but have fixed the normal sensitizer of hen serum necessary for a subsequent 

 hemolysis; the addition of heated hen serum answers this objection. 



