HEMOLYTIC SERA AND THEIR ANTITOXINS. 211 



lytic sera.* The important fundamental idea is that the bacterici- 

 dal (or cellulicidal) substance in various immune sera that endows 

 them with their properties is similar to the one found in normal 

 serum. This is the principle of the unity of the cytolytic substance 

 which we expressed in 1895 by saying that, in normal and in vacci- 

 nated animals, "the bactericidal substance is in general respects the 

 same, whatever may be the invading organism. In animals vacci- 

 nated against a given infective agent the bactericidal energy affects 

 that bacterium particularly, owing to the presence of the specific 

 preventive substance, which varies according to the micro-organ- 

 ism used in immunizing. It is owing to the intervention of this pecul- 

 iar preventive substance that the animal directs its destructive energy 

 against a given infective agent." 



In this description the word "bacterium" may be replaced by 

 the word "cell," referring to bacterium or blood corpuscles, as the 

 case may be. And further, a reservation should be made, based on 

 the subsequent study of hemolysis, that, although the alexin is the 

 same in normal and vaccinated animals of the same species, there 

 are certain differences in the alexins from different animal species. 

 The alexins of most animals, however, have the same essential char- 

 acteristics. We have already made another reservation, namely, 

 that certain normal sera contain, beside the alexin, other bactericidal 

 substances of less general import. The bactericidal substance for 

 B. anthracis in rat serum, for example, is certainly not an alexin. f 



As far as the absolute identity of the hemolytic with the bacterio- 

 lytic alexin in a given serum is concerned, it would seem to have 

 been firmly established in the present article. 



The fact, moreover, that "it is owing to the intervention of the 

 sensitizer that the animal directs its particular cellulicidal activity 

 against a given cell" is fully confirmed by the experiments detailed 

 in the first part of this article, experiments that prove, not only that 

 the same normal serum, but that the same alexin destroys at one time 

 a vibrio and at another a red blood cell depending on whether a 

 hemosensitizer or a cholera sensitizer is used. 



k* It is probably also applicable to the immune sera active against other cells, 

 such as the spermotoxic serum discovered by Landsteiner, the leucotoxic serum 

 )f Metchnikoff, and the epitheliotoxic serum of V. Dungern. 

 t Rat serum has in addition to this substance an alexin similar to that of other 

 jera. See note on p. 180. 



