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with the red cells of a sheep. This serum, there- 

 fore, was hsemolytic specifically for sheep blood 

 cells; i.e., it had increased solvent properties exclu- 

 sively for sheep blood cells. 



Basing his reasoning on his side-chain theory, 

 Ehrlich argued as follows: " If the haemolysin is 

 able to exert a specific solvent action on sheep 

 blood cells, then either of its two factors, the sub- 

 stance sensibilatrice of Bordet or the alexin of nor- 

 mal serum, must possess a specific affinity for these 

 red cells. It must be possible to show this experi- 

 mentally." Such in fact is the case, and the experi- 

 ments devised by him are as follows : 



Experiment i. Ehrlich and Morgenroth, as 

 already said, experimented with a serum that was 

 specifically hasmolytic for sheep blood cells. They 

 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 



