238 STUDIES IN IMMUNITY. 



which are more susceptible than others to the physical changes 

 in the surrounding fluid, should yield more readily to traces of 

 alexin. However this may be, this experiment does not deal 

 with sensitization by specific serum and therefore does not affect 

 our thesis that the same alexin can destroy various sensitized cells 

 energetically.* 



Neisser,t a partisan of the plurality of alexins in a given serum, 

 emphasizes experiments both by BailJ and by himself, the prin- 

 ciple of which is as follows : if a normal serum is mixed with cell A 

 (bacterium or blood cell), and, after a sufficient contact, centrifu- 

 galized, it is found that the supernatant serum has lost its property 

 of destroying cell A, but will still destroy cells B or C. Neisser 

 concludes from this that the alexin affecting A is not identical with 

 the one attacking B or C. 



The experiment contains a serious experimental error and con- 

 sequently any conclusion from it is erroneous. In the majority 

 of instances, when even large amounts of non-sensitized cells are 

 mixed with normal serum, they absorb only a small amount of alexin. 

 Our experiments just related as well as those with Gengou prove 

 this fact conclusively. Under these conditions the fluid still retains 

 its property of destroying subsequently added sensitized cells. It 

 is reasonable to expect, therefore, that if an unsensitized or feebly 

 sensitized cell is added to normal serum, for example corpuscles 

 of species A, there will soon be a state of equilibrium established 

 and a division of the alexin between the cell and the fluid; the 

 fluid, however, will retain the greater part. Hemolysis, moreover, 

 never goes beyond a certain point. It is quite possible that de- 

 stroyed corpuscles liberate a substance that prevents the fluid from 

 acting further on corpuscles of the same variety, without inhibiting 

 its effect on other varieties of corpuscles. In other words, a state 

 of equilibrium for corpuscle A may be far from being so for another 

 cell, which, when subsequently added, is destroyed by the fluid. 



In view of these facts we should not feel justified in saying that 



* The experiment, indeed, does not inform us as to whether the filtered serum 

 would have a varying hemolytic power for two different species of corpuscles, 

 each sensitized with specific heated serum. 



t Ueber die Vielheit der in normalen Serum vorkommenden Antikorper. 

 Deutsche med. Wochen., 1900, No. 49. 



t Archiv. fur Hygiene, 1899, Bd. XXV. 



