222 PROTOPLASMIC ACTION AND NERVOUS ACTION 



with the usual inorganic types of catalysis, is that 

 dependent on the activity of enzymes. Enzymes are 

 constant constituents of protoplasm, and their presence 

 accounts for many characteristic features of its chemical 

 performance. Enzyme-action, however, is obviously 

 responsible for only a portion of the metaboHc reactions, 

 especially the destructive or disintegrative ones, which 

 are largely hydrolytic. Although certain types of syn- 

 thesis are accelerated by enzymes under certain condi- 

 tions (dehydrolytic synthesis of esters, carbohydrates, 

 and apparently polypeptides), others cannot be thus 

 accounted for; e.g., photosyn theses, synthesis of fat 

 from protein or carbohydrate, or other syntheses involv- 

 ing the expenditure of much energy. Moreover, the 

 responsiveness of protoplasm to stimulation is not thus 

 explained, since enzymes show no such instantaneous 

 and marked acceleration of their action, under electrical 

 or mechanical influence, as is shown by Hving protoplasm. 

 As we shall see later, changes in protoplasmic structure 

 seem to be primarily responsible for the immediate 

 chemical effects following stimulation. 



Enzymes are simply colloidal catalyzers of complex 

 and specific chemical constitution. A part of their 

 catalytic acti\dty presumably depends on their colloidal 

 state; i.e., a state of subdivision making surface-condi- 

 tions of preponderant importance in their chemical 

 behavior. The general conditions of heterogeneous 

 catalysis thus apply to enzyme action; in addition there 

 are special conditions referable to the specific stereo- 

 chemical configuration of the enzyme molecule. 



It is well known that finely divided material of various 

 kinds (material with large surface-extent) is often very 



