THE NATURE OF ENZYME ACTION 283 



increase of velocity of reaction is, within limits of course, 

 proportional to the concentration of the catalyst, and also that 

 no energy is added to the system by its presence. The fact 

 that when the falling block has reached the bottom of the slope 

 the energy developed by its fall is the same whether it fell 

 rapidly or slowly calls attention to yet another important 

 property of catalysts, which consists in the fact that a small 

 quantity will, in the end, produce as much effect as a larger 

 one, provided that it be given a longer time to act, on the 

 understanding that during this longer time the catalyst itself 

 remains intact. 



As a rule these bodies are very active, so that it is usually 

 taken as one of their characteristics that they act in extremely 

 low concentrations compared to those of the bodies acted upon. 



When we now turn again to the living organism, with the 

 properties of catalysts in our minds, we note that bodies 

 answering to this description have for many years been prepared 

 from various cells and tissues. To mention one or two only, 

 we have diastase from malt, which converts starch to maltose ; 

 pepsin from the stomach, which splits up various proteins 

 into peptones ; peroxydase, which separates active oxygen from 

 various organic peroxides ; and so on. These various prepara- 

 tions were originally called "ferments," but owing to a certain 

 confusion between the organism producing certain changes — 

 yeast, for example — and the chemical substance by whose 

 agency the changes are produced, it was suggested by Kiihne 

 to call these chemical agents " enzymes," expressing the fact 

 that invertase — one of the earliest known — was contained in 

 yeast (eV £v/j,rf). The name has come into general use, though 

 " ferment " is also frequently used. 



" Enzymes," then, are the organic catalysts met with in the 

 living cell. They have certain properties in addition to those 

 already mentioned, one of which is that of being destroyed 

 by a temperature of from 50 to 70 C, probably due to their 

 being colloidal in nature. In contradistinction to the changes 

 produced by living protoplasm, their activities are not prevented 

 by the presence of antiseptics, such as chloroform or toluol, 

 although in certain cases these substances have a more or less 

 retarding action. 



Although, as yet, none of the enzymes has been prepared 

 synthetically, and their only source is the living organism, it 



