88 PHYSIOLOGY OF ALIMENTATION. 



reason that an optimum temperature exists in the case of 

 all ferments. By this is meant the temperature at which 

 the particular ferment under the given conditions brings 

 about its characteristic effects most rapidly that is to say, 

 its reaction velocity is greatest. This optimum tempera- 

 ture lies, for most ferments, close to 40 C. 



The reason for the existence of such a maximal reaction 

 velocity can be readily understood from what has been 

 said before. If the ferment remained unchanged upon 

 heating a reaction mixture, the velocity of the chemical 

 reaction would increase progressively with an increase in 

 temperature, just as in any ordinary reaction mixture. When, 

 however, we are dealing with reactions in which ferments 

 are concerned, the ferment is all the time undergoing a 

 decomposition itself, and the rate of this decomposition is 

 also a function of the temperature. It is known, in general, 

 that the length of time required to destroy a ferment at a 

 comparatively low temperature is greatly reduced by an 

 elevation of only a few degrees centigrade. TAMMANN, who 

 has worked out the velocity of the decomposition of the 

 ferment synaptase (emulsin) above 60 C., finds that an 

 increase in temperature of 10 C. multiplies the decom- 

 position velocity of the ferment by more than seven. In a 

 reaction mixture in which a ferment is concerned we have 

 therefore at least two reactions going on side by side, and 

 it is the product of these two simultaneously occurring 

 reactions which is represented by a curve that attains a 

 maximum at one point. Since the two reactions which yield 

 this curve have their individual characteristics, it can be 

 readily understood why the curves not only of different 

 enzymes, but even of the same enzyme acting under different 

 external conditions, must vary. In Fig. 18 are shown the 

 curves representing graphically the changing reaction veloc- 

 ities of various ferments with variations in the temperature. 

 Curves 1, 2, 3, and 4 illustrate the behavior of indigo enzyme 

 obtained from various sources; carve 5 that of synaptase 



