B ACT ERIOLY SINS AND H&MOLYSINS 53 



action of these two substances Bordet explains by 

 assuming that the red cell is not vulnerable to the 

 alexin ; just as, for example, there are certain sub- 

 stances that will not take a dye without the previous 

 action of a mordant. The substance sensibilatrice 

 plays the role of mordant. It makes the blood 

 cells vulnerable to the alexin, so that the latter can 

 attack the cells and dissolve them. The alexin he 

 regards as a sort of ferment body with digestive 

 powers. 



Bordet says further, that the substance sensi- 

 bilatrice sensitizes the blood cells not only for the 

 alexin derived from the serum of the same species 

 as that from which it (the substance sensibilatrice) 

 is derived, but sensitizes such cells also for the 

 alexins of normal sera of other species. For ex- 

 ample, in the foregoing experiment of Bordet, the 

 substance sensibilatrice derived from the guinea 

 pig by treatment with rabbit blood sensitizes the 

 red blood cells of rabbits not only for the alexin 

 of normal guinea pig blood, but also for the alexins 

 of other normal sera. In another experiment 

 this author showed that rabbit red cells sensitized 

 with an inactive specific haemolytic serum derived 

 from a guinea pig would dissolve rapidly on the 

 addition of normal rabbit blood. Here, then, the 

 rabbit red cells, sensitized (according to Bordet) by 

 the substance sensibilatrice of the guinea pig, dissolve 

 on the addition of the alexin of their own serum. 



