THE SENSITIZERS OF SERA. 243 



fix the sensitizer of the immune serum, and the decanted serum is 

 deprived of its specific properties. But blood cells fix substances 

 other than sensitizers. If we add corpuscles to fresh immune serum 

 instead of to heated serum, they deprive the fluid, as Bordet* proved, 

 of both sensitizer and alexin. This same phenomenon of alexin 

 absorption also occurs if a mixture of heated hemolytic serum and 

 fresh normal serum is employed instead of fresh hemolytic serum; 

 we know from the experiment of Bordet, to which reference has 

 been made, that an immune serum is completely regenerated on the 

 addition of fresh normal serum and becomes quite as active as it 

 was before being heated. But how may the absorption of alexin 

 in this mixture of corpuscles, alexin and suitable sensitizer be de- 

 tected? The matter is quite simple: fresh sensitized cells, say 

 cholera vibrios, treated with heated cholera serum, are added to 

 the mixture. If there is still alexin present, the sensitized vibrios 

 subsequently introduced will certainly undergo granular transforma- 

 tion, but if they remain intact it shows that the alexin has disap- 

 peared from the fluid. This experiment may be reversed by mixing 

 the alexin with the vibrios plus heated cholera serum and then 

 adding sensitized corpuscles: in this instance it is the vibrios that 

 absorb the alexin and are destroyed, and the subsequently added 

 corpuscles remain intact. 



From these experiments Bordet drew the conclusion that the 

 alexin that is fixed by and that destroys sensitized blood cells is 

 identical with the alexin that acts on sensitized bacteria. In a given 

 serum, then, there would be only one alexin attacking bacteria and 

 corpuscles indifferently. Whether we agree with this observer as 

 to the unity, or at least the functional unity, of this substance, 

 or with Ehrlich and Morgenroth in believing that a normal 

 serum contains a large number of different alexins, each particularly 

 adapted for a given cell or bacterium, the fact remains that, in 

 presence of a suitable sensitizer, a bacterium or a cell deprives fresh 

 serum of its alexin and renders it inactive either for the same cell 

 or for other sensitized cells. 



It is hardly necessary to state that in these experiments the 

 alexin, obtained as a rule from fresh serum of the rabbit or guinea- 

 pig, is not absorbed by the cells unless a sensitizer is present. In 



* See p. 191. 



