226 INFECTION AND IMMUNITY 



be destroyed by heating to 56° C, but "reactivated" by the addition of 

 fresh normal serum. He had thus produced an immune hemolysin, 

 just as Pfeiffer had produced immune bacteriolysin, and had demon- 

 strated the complete paralleUsm which existed between the two phe- 

 nomena. 



A practical test-tube method was thus given for the investigation of 

 the lysins, just as a practical test-tube method for antitoxin researches 

 had been developed by Ehrlich in his ricin-antiricin experiments. 



The path of investigation thus pointed out by Bordet was soon ex- 

 plored in greater detail by Ehrlich and Morgenroth.' The reasoning 

 which Ehrlich had applied in explaining the production of antitoxins 

 was thought, by these observers, to be equally appUcable to the phe- 

 nomena of bacteriolysis and hemolysis. 



Since the thermolabile substance or alexin, renamed by Ehrlich 

 " complement," was already present in normal serum and had been shown 

 to be little, if at all, increased during the process of immunization, 

 this substance could have but little relation to the changes taking place 

 in the animal body as immunity was acquired. The more stable serum- 

 component, however, the "substance sensibilisatrice " of Bordet, or, 

 as Ehrlich now called it, the "immune body," was the one which seemed 

 specifically called forth by the process of active immunization. Ehrlich 

 argued, therefore, that when bacteria or blood cells were injected into 

 the animal, certain atom-groups or chemical components of the injected 

 substances were united to other atom-groups or "side chains'' of the 

 protoplasm of the tissue cells. These "side chains" or receptors, then 

 reproduced in excess and finally thrown free into the circulation, con- 

 stituted the "immune body." The immune body, therefore, he con- 

 cluded, must possess atom complexes which endow it with specific 

 chemical affinity for the bacteria or red blood cells used in its produc- 

 tion. This contention was supported by Ehrlich and Morgenroth by 

 an ingenious series of experiments. 



Having in their possession, at that time, the blood serum of a goat 

 immunized against the red blood ceUs of a sheep, they inactivated it 

 (destroyed the complement or alexin) by heating to 56° C. The serum 

 then contained only the "substance sensibilisatrice" or immune body. 

 To this inactivated serum they added sheep's red corpuscles, without 

 obtaining hemolysis. Having left the inactive serum and the sheep's 

 corpuscles in contact with each other for some time, they separated 



1 Ehrlich und Morgenroth, Berl. klin. Woch., 1, 1899. 



