28 EXPERIMENTAL RESEARCHES 



province of the physiology of stimulation. 

 Light, however, has been thrown on the sub- 

 ject of the specificity of reactions by the view I 

 have expressed that the receptors of the cell- 

 protoplasm are the seat of the process, and that 

 their regeneration and elimination are the con- 

 sequences of this. Supposing these processes 

 to occur in the normal organism, and to be 

 merely intensified in the case of active immuni- 

 sation, it is possible to understand that antibodies 

 of the most varied kinds may exist in the serum 

 of the normal organism, and also to comprehend 

 the processes of immunity by viewing them from 

 the standpoint of the physiology of nutrition and 

 metabolism. Thus I am glad to be able, by my 

 conception of the problem, to come into entire 

 agreement with Metchnikoff. The immense 

 number of exceedingly various substances which 

 possess haptine characters in the blood serum, 

 substances of whose existence at one time one 

 did not even dream, is thus to be explained as 

 an expression of a many sided and differentiated 

 action of the most varied organs. One may 

 already by simple means differentiate the mul- 

 titude of serum substances into antitoxins, 

 amboceptors, agglutinins, precipitins, opsonins, 

 complements, ferments, antiferments, etc., but a 



