76 IMMUNE SERA 



must note particularly the researches of Ehrlich 

 and Morgenroth. 1 These authors asked themselves 

 the following questions: (i) What relation does 

 the haemolytic serum or its two active components 

 bear to the cell to be dissolved? (2) On what 

 does the specificity of this haemolytic process 

 depend ? Ehrlich was led to these researches partic- 

 ularly by his so-called Side-chain Theory, which 

 we shall examine in a moment. 



He made his experiments with a haemolytic 

 serum that had been derived from a goat treated 

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

 fore, was haemolytic 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 haemolytic for sheep blood cells. They 



1 See the various papers in "Collected Studies on Immunity," 

 Ehrlich- Bolduan, Wiley & Sons, New York, 1910. 



