THE ACTION OF AMYLASE ON STARCH 117 



The above experiments show the analogy which exists 

 between the action of enz}Tnes and the action of organisms. 

 They can, however, be differentiated by certain other pro- 

 perties. Thus some enzymes, e.g., invertase, will pass readily 

 through a porous porcelain filter, which under similar con- 

 ditions will retain all living organisms. Further, certain 

 antiseptics which inhibit the action of micro-organisms are 

 without effect on enzymes ; among these the most frequently 

 used are thymol, chloroform, and especially toluene. 



It has also been found that when the amount of substance 

 to be acted upon is large in proportion to the quantity of 

 enzyme used, then the amount of reaction taking place is 

 proportional to the quantity of enzyme present ; this is 

 known as the hw of proportionality. The following experi- 

 ments may serve to illustrate it :— 



Two lots of 300 c.c. each of 3 per cent, starch solution 

 are taken ; to one is added ^ c.c. of malt extract, to the 

 other 2 c.c. of the same extract, and the two mixtures heated 

 for a quarter of an hour at 50° C. Upon titration with 

 Fehling solution it wiU be found that the greater amount of 

 reaction has taken place in the solution to which the larger 

 quantity of malt extract was added. 



