4 IMMUNE SERA. 



amount of the serum of a normal guinea-pig was 

 added (a serum which of course was not haemolytic 

 for rabbit red cells), the full haemolytic power was 

 restored to this inactive serum. In other words, 

 it had been reactivated by this addition. 



This experiment permits of only one conclusion, 

 namely, that the hasmolytic action of the specific 

 haemolytic serum depends on two substances. One 

 of these is able to withstand heating to 55 C., and 

 is contained only in the specific serum. The other 

 is destroyed by heating to 55 C. and is contained 

 not only in the specific haemolytic serum, but also 

 in the serum of normal untreated animals. 



Alexin and Substance Sensibilatrice of Bordet Role of 

 the Substance Sensibilatrice. Previous to this work 

 of Bordet, and especially as a result of the researches 

 of Buchner, it had been known that there were con- 

 stituents of normal blood-serum which were ac- 

 tively destructive to corpuscular elements, bac- 

 teria, and other cells with which they came in con- 

 tact. These substances had been termed alexins 

 by Buchner. This term was retained by Bordet 

 to designate that constituent of normal serum 

 which did not withstand heating to 55 C., and 

 which was one of the factors in the haemolytic 

 process. The other substance, which was found 

 only in the specific serum and which withstood 

 heating to 55 C., he termed substance Sensibilatrice. 



According to Bordet, therefore, the substances 

 required for haemolysis are the substance sensibila- 



