396 CHEMICAL DYNAMICS 



hydrolytic dissociation. When the salt formation is at any 

 instant extensive then, as Stieglitz points out, although in every 

 respect the mechanism of the acceleration of the hydrolysis by 

 the catalysing acid is the same, yet a definite shift in equilibrium 

 results from the presence of the catalysor and, concurrently, the 

 catalysor is in some measure used up during the progress of the 

 reaction and some energy has to be expended in order to recover 

 it, unaltered, from the system in its final condition of equilibrium. 

 I quote from Stieglitz' article : * 



"In accordance with the results, our views concerning catalytic 

 action must be modified in regard to all three of the commonly 

 assumed fundamental characteristics of catalytic action, (1) that 

 the acceleration must be proportionate to the concentration of 

 the catalytic agent present; (2) that the agent must not appear 

 to combine with any of the substances undergoing change; and 

 (3) that the ultimate condition of equilibrium must not be 

 measurably modified by the presence of a catalysor. These 

 characteristics are practically true only for limiting cases where 

 the amount of salt-formation is so small as to be beyond the 

 scope of our measurements. None of them is absolutely true 

 under any conditions. When the amount of salt-formation 

 becomes measurable, as for iminoesters, they need not hold even 

 approximately, and still the fundamental mechanism and mode 

 of the catalysis is the same in these cases as in the others. The 

 one vital fact, then, of an acceleration due to an increase in the 

 active mass or concentration of a reacting component in a cata- 

 lytic action is the only fundamental fact common to all catalytic 

 actions. " 



With this enlarged conception of catalysis in mind we need 

 no longer have scruples in regarding the fermentative reactions 

 as instances of true catalysis. They exhibit the essential phe- 

 nomenon of acceleration through the presence of a chemical 

 agency which is added to the system, in other words the ferment. 

 Our task is therefore, not to compare the fermentative reactions 

 with a special and arbitrarily chosen class of catalytic reactions 

 but, as in all instances of catalysis, to attempt to unravel the 

 chemical mechanism of the observed acceleration. 



In a system so complex as that afforded by a protein mixed 

 with an enzyme in aqueous solution several possibilities present 

 * Julius Stieglitz (127). Cf. also Hans Euler (26). 



