H&MOLYSINS. 15 



Nomenclature. In place of the name substance 

 sensibilatrice Ehrlich first introduced the term 

 immune body, later on he called it the amboceptor. 

 In the following pages we shall use the term immune 

 body, as this had already been used by R. Pfeiffer 

 to designate the same substance in bactericidal 

 serum. Other names proposed for this substance 

 have been substance fixatrice by Metchnikoff, copula, 

 desmon, preparator by Miiller. Instead of the name 

 alexin, Ehrlich now uses the term complement in order 

 to express the idea that this body completes the 

 action of the immune body. 



In contrast to the specific affinity which the red 

 cells possess for the immune body, these cells pos- 

 sess no affinity whatever for the alexin, as has been 

 shown by the second of Ehrlich's experiments. 

 The alexin, therefore, possesses no combining group 

 which can attach itself directly to the red blood- 

 cell. It acts on these cells only through an inter- 

 mediary, the immune body, which therefore must 

 possess two binding groups, one which attaches to 

 the red blood-cell and the other to the alexin of 

 normal serum. As already stated, the group 

 which attaches to the red blood-cell possesses a 

 much stronger affinity than that which combines 

 with the alexin. This follows from the last two 

 experiments of Ehrlich before cited, in which he 

 showed that at the lower temperature and with 

 both substances present with the blood-cells only 

 the immune body combined with the cells, while 



