HEM HAL M EC II . I NIC8 IN LIVING PLANT 643 



known, and most of them are specifically constituted to 

 effect the hydrolysis, oxidation, reduction or splitting of 

 some definite organic compound or group of compounds 

 containing similar radicals. 



Innumerable enzymes have in late years been isolated 

 from the plant-body, so that it would seem that there is 

 none present to catalytically accelerate each of the slow 

 single changes that in the aggregate make up the complex 

 metabolism of the plant. 



The law of mass applies with equal cogency to aituhitic 

 reactions. If twice the amount of acid is added to a so- 

 lution of cane-sugar (or twice the amount of enzyme) 

 then the reaction velocity is doubled, and hydrolysis pro- 

 ceeds twice as fast. As the catalyst is not destroyed by 

 its action, but is continually being set free again, the con- 

 centration of the catalyst remains the same throughout the 

 reaction ; while, on the contrary, the amount of cane sugar 

 continually decreases. 



If the catalyst be present in great excess the amount 

 of hydrolysis will be limited by the amount of cane-sugar 

 present, and as this is used up so the reaction will prog- 

 ress by a logarithmic curve as in Fig. 1, A. In this case 

 B may represent, the amount of catalyst. If, on the con- 

 trary, there is a large amount of sugar and very little 

 acid or enzyme present, so that the catalyst becomes the 

 limiting factor, then we happen upon a novel state of 

 things; for by the law of mass the rate of hydrolysis 

 will now remain constant for some time till the excess of 

 sugar is so far reduced that it in turn becomes a limiting 

 factor to the rate of change. In this case the velocity 

 curve would consist of a first phase with a straight hor- 

 izontal line of uniform reaction-velocity leading into the 

 second phase of a typical falling logarithmic curve (see 

 Fig. 1, C). These conditions have been experimentally 

 examined by Horace Brown and Glendinning, and fully 

 explained and expounded by E. F. Armstrong in Part II 



'Pro* Hoy. So,\, Vol. LXXm, 1904, p. 511. 



