70 INTRODUCTION TO GENERAL PHYSIOLOGY 



Is there any evidence of similar action in the case of enzymes? 

 What evidence there is, is naturally more or less indirect ; but it is 

 in favour of a preliminary adsorption of the reacting substances 

 on the surface of the enzyme. It lies, in great part, in the facts 

 concerning the rate of the reaction in relation to the amount of 

 the enzyme present, and cannot be discussed here (P., p. 315). 

 There is also an interesting retarding effect of certain inert sub- 

 stances, such as saponin, whose action, as a whole, can only be 

 explained by its great lowering of surface energy, thus obtaining 

 possession of the enzyme surface, and displacing more or less the 

 other constituents of the system from that surface. This is similar 

 to the effect of impurities on Faraday's platinum, and "it has the 

 negative temperature coefficient characteristic of surface tension. 



But there are a great number of enzymes known to us, each 

 of which causes acceleration in one particular kind of reaction only, 

 a fact at first sight difficult to reconcile with mere condensation 

 on a surface. It might be supposed that one enzyme only would 

 suffice for all purposes. At present, however, we have not sufficient 

 knowledge of the numerous properties of surfaces to be able to 

 exclude the probability that surfaces of different chemical structure 

 have different powers of adsorption with regard to the various 

 chemical natures of the components of the reactions which they 

 influence. It is, moreover, not improbable that the rate of a 

 reaction may be increased on a surface in a way additional to that 

 of mass action. In the act of condensation, molecular forces may 

 be brought into play, which raise the chemical potential of the 

 reacting substances ; in other words, increase their affinity for each 

 other. 



On the whole, the following view is that which is most in 

 agreement with the facts. Owing to the nature of its surface, 

 each variety of enzyme has the property of causing condensation 

 thereon of the components of a particular system. This results 

 in a greatly increased rate of attainment of the natural equilibrium 



that system ; whether merely by mass action or by increase of 

 chemical potential in addition, is as yet uncertain. 



Changes in Carbohydrates 



We may now return to the fate of starch after being subjected 

 to the action of an enzyme in the mouth, which brings about 

 its ultimate conversion to glucose (E., p. 193). The enzyme in 

 question is called ainylase, because it acts on starch (amylum). 

 This action, although a rapid one, has not time to be completed, 

 and does not progress further than the formation of some com- 

 pounds intermediate between starch and glucose, namely, dextrin, 



