SYNTHESIS OF FATS ACCOMPANYING INTESTINAL ABSORPTION 49 
In any given reaction the greater the difference in chemical potential, as 
measured by difference in heat of formation of the substances present at either end 
of the reaction, the more completely will the reaction run towards that side at which 
the chemical energy is at a minimum, and the greater will be the velocity of 
reaction. 
In all reactions which are induced or accelerated by enzymes, the change in 
chemical energy is small, and it is for this reason that all such enzymic changes as 
digestion of proteids and hydrolysis of fats, starches, and sugars run with measurable 
velocities, and are, under certain conditions, reversible. 
The function of the enzyme in accelerating such reactions or starting them 
when in complete abeyance, consists in increasing, in some manner, the difference 
in chemical potential in the solution. 
It is only by an alteration in the difference in chemical potential that a reaction 
proceeding, with given concentration at a given temperature, can be altered in velocity ; 
and in certain cases, even where the reaction when once started is markedly exo-thermic, 
the difference in chemical potential must be increased before the reaction starts. 
The need for such an increase in the difference of the chemical potential is still 
more obvious when the amount of energy set free in the reaction is small, as in all 
cases ot enzymic action. 
Hence, in a great many cases, the action remains stationary until the enzyme 
is added. 
Also different enzymes cause varying amounts of alteration in chemical 
potential, and hence the reaction stops at different stages with different enzymes. 
Thus in the hydrolysis of starch to glucose, one enzyme stops at the stage of 
maltose, while another is capable of causing a sufficient amount of change of chemical 
potential to carry the hydrolysis on into glucose. 
The above view of catalysis as a change due to alteration in chemical potential 
111 a chemically reacting system, differs in certain respects from that enunciated by 
Ostwald, 1 and now usually accepted. 
According to Ostwald, the action of a catalyser is merely that of accelerating 
(or retarding) a reaction which is already proceeding, it may be at an immeasurably 
slow rate, the catalyser itself not being altered in the reaction or adding energy to it, 
so that the point of equilibrium cannot be altered by the presence of the catalyser. 
In other words, a catalyser merely acts upon the velocity of reaction, but 
cannot alter the end result or start a reaction which would not occur, provided a 
sufficiently long time interval were allowed to elapse, without its presence. 
The view stated in this paper, however, is that a catalyser or enzyme may 
not only alter the velocity of a reaction, but may start a reaction which would not 
proceed at all in its absence, and may further alter the point of equilibrium of the 
reaction. 
I- Uber Katalyse. Vortrag gehaltcn auf der 73 NaturforscAerversammlung an Hamburg, 1901. Leipzig, S. Hirzcl, 1902. 
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