*4 IMMUNE SERA. 



sibilatrice, but had left the alexin practically un- 

 touched. 



It still remained to show the relation of these 

 two substances to the red cells at higher temper- 

 atures. At 37-4o C., as already mentioned, 

 haemolysis occurs rapidly, beginning usually within 

 fifteen minutes. It was possible, therefore, to 

 leave the cells and serum in contact for not over 

 ten minutes. Then the mixture was centrifuged 

 as before. The sedimented blood-cells mixed with 

 normal salt solution showed haemolysis of a moder- 

 ate degree. The solution became complete when 

 a little normal serum was added. The supernatent 

 clear fluid separated by the centrifuge did not dis- 

 solve sheep red cells. On the addition, however, 

 of substance sensibilatrice it dissolved them com- 

 pletely. 



So far as concerns the technique of the experi- 

 ments, I should like to observe that the addition 

 of red cells in this as well as in all the following 

 experiments was always in the form of a 5% mix- 

 ture or suspension in .85%, i.e. isotonic, salt solu- 

 tion. 



The significance of the last of the above-cited 

 experiments is at once apparent. It is that the 

 substance sensibilatrice possesses one combining 

 group with an intense affinity (active even at o C.) 

 for the red cell, and a second group possessing a 

 weaker affinity fone requiring a higher temperature) 

 for the alexin. 



