SENSITIZING ANTIBODIES 279 



Bordet 9 now observed that the blood serum of guinea-pigs 

 previously treated with the defibrinated blood of rabbits developed 

 marked powers of dissolving rabbits' corpuscles, and that this 

 hemolytic action could 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 im- 

 mune bacteriolysin, and had demonstrated the complete parallelism 

 which existed between the two phenomena. 



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 ex- 

 periments. 



The path of investigation thus pointed out by Bordet was soon 

 explored in greater detail by Ehrlich and Morgenroth. 10 The rea- 

 soning which Ehrlich had applied in explaining the production of 

 antitoxins was thought, by these observers, to be equally applicable 

 to the phenomena 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 im- 

 munization, 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 sen- 

 sibilisatrice " 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 repro- 

 duced 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 

 production. This contention was supported by Ehrlich and Mor- 

 genroth by an ingenious series of experiments. 



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



9 Bordet, Ann. de 1'inst. Pasteur, t. xii, 1898. 



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



