CONDITIONING FACTORS 469 



as well since ; for example, the proteases papain and bromelin 

 of the papaw and pineapple respectively hydrolyse fibrin best 

 as Pj, 7-2, but peptone or gelatine at Pj, 5. 



3. CONCENTRATION OF ENZYME AND OF SUBSTRATE. 



According to the Law of Mass Action enunciated by 

 Guldberg and Waage, the rate at which a body undergoes 

 chemical change is dependent on the concentration as 

 measured by the number of gram molecules of substance 

 present in the litre ; consequently the amount of substance 

 changed in unit time will be greater at the beginning of the 

 reaction than towards the end, since the amount of un- 

 changed substance is continually decreasing. 



The relationship between the amount of substance x 

 (measured in gram molecules per litre) changed in time t 

 (measured in minutes) and the original concentration a of the 

 substance is given by the equation — 



7 '"^ {a - x)- 



The above formula holds only for the decomposition of a 

 single substance, and it is, therefore, characteristic of what is 

 known as a monomolecular reaction or a reaction of the first 

 order, and as such is applicable to all cases of hydrolysis, as 

 for example — 



CiaH^.On + H,0 = ^C^li^■^0^ 



Although from the left-hand side of the equation it would 

 appear that two substances are reacting, the quantity of water 

 present is so large, as compared with the amount of cane 

 sugar, that its concentration is practically unaltered, and 

 therefore, for all intents and purposes, only a single substance 

 is undergoing alteration in concentration. 



Now the hydrolysis of cane sugar which takes place 

 slowly in aqueous solution is catalytically accelerated by the 

 addition of dilute mineral acids, the effect being greater in 

 proportion to the amount of acid used, without, however, 

 altering the order of the reaction. In reactions acting in 

 accordance with the logarithmic equation above given, the 

 amount of substance changed in a given time bears a constant 



