CHAPTER XI 



VELOCITY OF REACTION, AND THE COMPARATIVE ACTION 

 OF ENZYMES AND CELLS 



EXPERIMENTAL OBSERVATIONS ON VELOCITY OF REACTION, AND 

 THEIR DISCUSSION ALTERATION OF CONCENTRATION OF 

 ENZYME. 



THE investigations of the conditions of equilibrium have shown 

 that at a certain point in the reaction, at which the molecular 

 concentrations or osmotic pressures of the different substances 

 in solution and taking a part in the reaction bear a definite pro- 

 portion to one another, there is no energy set free as a result of 

 the reaction, and hence that the system is in equilibrium at this 

 point. At all other points or stages in the reaction energy is set 

 free as the result of the reaction, and hence the question arises, 

 Why is a stationary position possible in the system at any other 

 point in the reaction than the equilibrium point ? If a system 

 contains substances capable of reacting with one another and 

 present at other concentrations than those of the equilibrium 

 point, energy will be set free by any movement towards the 

 equilibrium point ; why then is the equilibrium point not instantly 

 reached and the energy set free ? Why, in some instances, is there 

 a slow and measurable velocity of reaction towards equilibrium 

 which may not be reached for days or weeks ? Why, in other 

 cases, is there no measurable movement at all towards the position 

 of equilibrium, although the substances are left in solution for an 

 indefinite time, until certain substances not permanently altered 

 themselves in the slightest degree are added to the solution, and 

 after the addition of such substances why does the reaction at once 

 commence and continue until equilibrium is attained ? That is, 

 why do catalysts in general (and enzymes, which form a particular 

 class of catalysts formed by the agency of living cells) induce 

 reactions which cannot be shown to proceed in their absence, or 

 cause reactions which proceed with infinite slowness to be hastened 

 into a measurable velocity? Finally, in many reactions in living 



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