RELATIONS OF SENSITIZERS TO ALEXIN. 379 



guinea-pig corpuscles become laden with sensitizer and alexin and 

 are therefore susceptible to absorb the colloidal substance which 

 brings about agglutination and facilitates hemolysis. 



Which of the two sera is it that produces the sensitization? We 

 have already seen that heated bovine serum contains a sensitizer 

 inasmuch as its addition to a mixture of corpuscles and guinea-pig 

 alexin produces a distinct hemolysis. This sensitizer may produce 

 some effect in the experiment, but it is by no means necessary, 

 because we have already found that heated bovine serum treated 

 with guinea-pig corpuscles and thereby deprived of its sensitizer 

 for these corpuscles retains intact its property of endowing fresh 

 horse serum with a hemolytic property. It is, moreover, easy to 

 understand why the bovine sensitizer is not necessary inasmuch 

 as another sensitizer of superior potency is present in Ehrlich and 

 Sachs' experiment. This is the sensitizer contained in fresh horse 

 serum in addition to the alexin.* 



Our interpretation of Ehrlich and Sachs' experiment is there- 

 fore the following: When guinea-pig corpuscles are added to a 

 mixture of the two sera they are affected by the sensitizer of the 

 horse serum and to a certain extent by the sensitizer in heated 

 bovine serum. This second sensitizer is, however, superfluous. 

 Its presence is by no means necessary for the experiment. When 

 this sensitization is effected the corpuscles are then in a condition 

 to fix the horse alexin. This alexin, however, has only slight hemo- 

 lytic power. But once the corpuscles have become sensitized and 

 laden with alexin, they are modified in their properties of molec- 

 ular adhesion to such an extent that they become able to attract 

 the colloidal substance of bovine serum, which unites with them. 

 The adhesion of this new substance produces two results: It causes 

 the blood corpuscles to be more easily destroyed by alexin and 

 also agglutinates them energetically. Consequently, a powerful 

 clumping followed by hemolysis is observed. 



This interpretation explains all the facts that have been noted 

 by Ehrlich and Sachs. It is evident, for example, that: (a) bovine 

 serum (56 degrees) that has been treated with guinea-pig corpuscles 

 will retain its property of forming a hemolytic mixture with horse 



* It is to be recalled that the demonstration of this sensitizer is easy. Guinea- 

 pig corpuscles are hemolyzed by a mixture of guinea-pig alexin and horse serum. 



