242 STUDIES IN IMMUNITY. 



showed that the bacteriolytic property of anticholera serum neces- 

 sitates the collaboration of two substances: one, the specific pre- 

 ventive substance, or sensitizer as he called it, formed during 

 immunization in the animal, and able to resist rather high temper- 

 atures (65-70 degrees) ; the second, Buchner's alexin, occurring in the 

 serum of normal as well as of immunized animals, disappearing 

 rapidly on standing, and easily destroyed by heat (55 degrees). The 

 alexin alone has little effect on normal vibrios, but becomes infinitely 

 more active when the vibrios have been acted on by a specific 

 sensitizer. 



This idea of the duality of the bacteriolytic substances was 

 established by Bordet in 1895 by means of a series of experiments, 

 of which the following is the most important: Heating cholera 

 serum to 55 degrees deprives it of its bacteriolytic properties, 

 but, on adding fresh serum from a normal animal to this heated 

 serum, the latter entirely recovers the energetic property it 

 possessed before being heated. In other words, fresh normal 

 serum " reactivates " heated cholera serum. Indeed, the two 

 substances, the collaboration of which is necessary, are present 

 in such a mixture. 



The alexin, as Metchnikoff and his school have shown, is leuco- 

 cytic in origin; even the destruction of vibrios within the leucocytes 

 of normal animals is due to this alexin, as is evident from Metch- 

 nikoff's studies on phagocytosis. 



Bordet* later injected animals with red blood cells of other 

 species in the place of vibrios. The serum of such animals ac- 

 quires the property of hemolyzing in vitro the corpuscles used for 

 injection, and this hemolysis is also due to the collaboration of 

 two substances : the normal alexin, destroyed by heating to 55 de- 

 grees, and an acquired sensitizer.. What, then, are the intimate 

 reactions between the active substances of the serum and the 

 sensitive cells? 



We know that if a suitable immune serum, previously heated to 

 55 degrees, is added to its specific red blood corpuscles, there 

 is no hemolysis because the alexin has been destroyed. Ehrlich and 

 Morgenrothf showed that under such conditions the corpuscles 



* See p. 134. 



t See Collected Studies on Immunity. Ehrlich-Bolduan. John Wiley & 

 Sons, p. 1. 



