74 BACTERIAL METABOLISM ENZYMES 



certain enzyme actions; it consists in the fact that, although the 

 presence of the catalyst neither adds to nor subtracts from the 

 total energy change in the reaction, the form of this energy may be 

 altered. When the weight falls slowly by itself, nearly the whole 

 of the energy appears as heat due to friction along the glass plane, 

 so that the weight arrives at the bottom with very little kinetic 

 energy; on the contrary, when oiled, nearly the whole of the energy 

 is present in the weight at the end of its fall as kinetic energy, very 

 little friction having been met with in its descent. We may notice, 

 also, comparing the effects of different amounts of oil, that small 

 amounts produce a much more marked result than the subsequent 

 addition of further quantities. This is also characteristic of 

 enzymes, as we shall see later. 



"From what has been said it follows that a catalyst is merely 

 capable of changing the rate of a reaction already in progress. In 

 opposition to this it may reasonably be said that a reaction does 

 sometimes seem to be initiated. Such a case is that of a mixture 

 of oxygen and hydrogen gases caused to combine by spongy plati- 

 num. Now there are reasons for the belief that an extremely slow 

 combination is taking place at ordinary temperatures without 

 catalysis. One thing to be considered in reference to this belief 

 is the enormous acceleration of chemical reactions by rise of tem- 

 perature, the majority being about doubled by a rise of 10 C. In 

 this way a reaction having a velocity of 1 at would reach one 

 of 2 at 10, 4 at 20 and 1 X 2 10 = 1024 at 100. At the tempera- 

 ture of 500 there is appreciable formation of water in the case in 

 point, and Bodenstein (1899) has shown that if the velocity at 689 

 be represented by 163, that at 482 has already sunk to 0.28; so that 

 at room temperature the velocity would be quite incapable of 

 detection by chemical means, since centuries would be needed 

 to produce a fraction of a milligram of water. Grove's gas battery 

 also proves that the two gases are not in equilibrium at ordinary 

 temperatures, since electrical energy is obtained by their slow com- 

 bination. 



"To take another case of a reaction which progresses at a slow 

 rate when left to itself: When methyl acetate is mixed with water 

 at ordinary temperatures it is very slowly hydrolyzed to alcohol 

 and acetic acid until a certain proportion of it is decomposed, so 

 that a state of equilibrium is finally arrived at. This process takes 

 many days for its completion, but the time may be shortened to a 

 few hours by the addition of a small amount of hydrochloric acid. 



"The objection may be made to the former of these two examples 

 that the combination of oxygen and hydrogen does not take place 

 except in the presence of water vapor, which probably acts as a 

 catalyst. Similarly, the hydrolysis of esters by water may be said 

 to be due to the hydrion present therein. This point of view does 



