736 INTERNAL SECRETIONS AND PRESERVATION OP LIFE. 



It has been designated by M. Bordet under the name of 'sensi- 

 tizing substance' [fixative]. The second insignificant ['banale'] 

 substance, that found in normal sera, is the alexin of Buchner 

 and Bordet, or Ehrlich's complement." 



What is the active cytolytic constituent of the normal 

 serum? A material difference between Buchner's alexins and 

 Bordet's fixative, that is to say, between the trypsin-laden 

 cytase and the oxidizing substance, is the fact, recognized by 

 all, that the alexin, or cytase, is destroyed when exposed to a 

 temperature of about 56 C., while the fixative, or oxidizing 

 substance, can stand without harm a temperature of about 65 

 C. It becomes evident, therefore, that the agency disabled "by 

 heating to 55 to 56 C.," referred to by Metchnikoff, must 

 have been the alexin. But how did the addition of "a little 

 normal serum incapable itself of causing hcemolysis" restore the 

 serum's hsemolytic powers? It is clear that there must have 

 been something in the latter with which it could combine to 

 bring about the reaction necessary for the liberation of func- 

 tional energy to which we have referred. And what is the 

 nature of this required agency? The second portion of the 

 quotation furnishes a clue to its identity: i.e., the fact that, 

 while losing its power of dissolving red corpuscles, the serum 

 of a prepared or infected animal preserves its property of ag- 

 glutinating the latter. Indeed, this agglutination points to the 

 presence of fibrin, which, as interpreted from our standpoint, 

 is a phosphorus-laden body. But, then, how did haemolysis occur 

 when the normal serum was added? The fibrin on being ex- 

 posed to the action of the oxidizing substance could only have 

 liberated the agglutinated blood-corpuscles by causing dissolu- 

 tion of the fibrinous filaments, and without affecting the red 

 cells. The process evidently requires another agency: a body 

 which only becomes active in the blood when aided by the 

 energy liberated by the combination of fibrinogen and oxidizing 

 substance. 



Again, "M. Bordet has shown," writes Metchnikoff, "that 

 the serum of animals injected at various times with the blood 

 of foreign species contains almost the same quantity of alexin 

 as does normal serum. But, on the other hand, it is the sen- 

 sitizing substance [the fixative, oxidizing substance, etc.] which 



