60 IMMUNE SERA 



made this inactive by heating to 55 C., so that then 

 it contained only the substance sensibilatrice. 

 Next they added a sufficient quantity of sheep 

 red cells, and after a time centrifuged the mixture. 

 They were now able to show that the red cells had 

 combined with all the substance sensibilatrice, and 

 that the supernatant clear liquid was free from the 

 same. In order to prove that such was the case 

 they proceeded thus: To some of the clear centri- 

 fuged fluid they added more sheep red cells; and, 

 in order to reactivate the serum, a sufficient amount 

 of alexin in the form of normal serum was also 

 added. The red cells, however, did not dissolve 

 there was no substance sensibilatrice. The next 

 point to prove was that this substance had actually 

 combined with the red cells. The red cells which 

 had been separated by the centrifuge were mixed 

 with a little normal salt solution after freeing them 

 as much as possible from fluid. Then a little alexin 

 in the form of normal serum was added. After 

 remaining thus for two hours at 3 7 C. these cells 

 had all dissolved. 



In this experiment, therefore, the red cells had 

 combined with all the substance sensibilatrice, 

 entirely freeing the serum of the same. That the 

 action was a chemical one and not a mere absorp- 

 tion was shown by the fact that red blood cells of 

 other animals, rabbits or goats for example, exerted 

 no combining power at all when used instead of 



