72 IMMUNE SERA 



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 hsemolytic 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. 



Buchner, we have seen, applied the term alexins 

 to the constituents of normal serum which were 

 actively destructive to corpuscular elements, bac- 

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

 tact. This term was ^retained by Bordet to desig- 

 nate 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- 

 trice of the specific haemolytic serurn and the 

 alexin which exists even in normal serum. The 

 action of these two substances Bordet explains by 

 assuming that the red cell is not vulnerable to the 

 alexin; just as, for example, there are certain sub- 

 stances that will not take a dye without the previous 



