FERMENTS AND FERMENTATION. 87 



use of moist heat than dry heat. These facts seem to Indi- 

 cate that the decomposition of the ferment is accomplished 

 through the taking up of water in other words, that we 

 are dealing with a hydrolysis of the ferment. The pos- 

 sibility of a mere change in the physical state of the fer- 

 ment as the cause of its inactivation through heat must, 

 however, also be considered, for there are many reasons at 

 hand for believing that ferments owe their specific virtues 

 quite as much to their physical state of aggregation as to 

 their chemical make-up. 



The fact that ferments suffer a decomposition when 

 exposed to higher temperatures explains the peculiar be- 

 havior of chemical reactions which are being catalyzed 

 by ferments when the reaction mixtures are exposed to 

 various temperatures. As is well known, the velocity of 

 ordinary chemical reactions varies greatly with different 

 temperatures. An every-day illustration of this fact is 

 found in the use of heat to hasten chemical decomposi- 

 tion in our ordinary analytical reactions, and the resort to 

 refrigeration in the effort to delay decomposition in animal 

 and vegetable matter. For ordinary chemical reactions it 

 has been found that the reaction velocity is, roughly speak- 

 ing, doubled or trebled for every increase of 10 C. in tem- 

 perature. 1 When we are dealing with chemical reactions 

 which are taking place under the influence of a ferment, 

 things are entirely different. Within certain limits we 

 have here also an increase in reaction velocity with an in- 

 crease in temperature, but when a certain point is reached 

 which varies with different ferments, and with the same 

 ferment acting in different media the reaction velocity 

 no longer increases but decreases with a further elevation 

 of the temperature. Finally a point is reached at which 

 the reaction ceases entirely (apparently). It is for this 



1 COHEN: Physical Chemistry for Physicians. Translated by MARTIN 

 H. FISCHER, New York, 1903, p. 53. 



