ENERGY SUPPLY OF THE CELL 35 



Fermentation continues, and energy is liberated, after 

 growth has ceased. The surplus energy thus produced 

 appears largely in the form of heat. Motility and 

 production of light do not require measurable amounts of 

 energy. 



The surplus energy which appears ultimately in the 

 form of heat should not be considered as useless waste. 

 It may have served a purpose in the cell before appearing 

 as heat. Probably, energy potentials of some kind 

 must be maintained in the living cell to prevent detri- 

 mental reactions. The continuous equalization of these 

 potentials would result in the ultimate transformation 

 of the utilized energy into heat. 



II. CHEMICAL CONSIDERATIONS 



(a) ENZYMES OF FERMENTATION 



It has been proved in at least four different cases that 

 fermentation is caused by enzymes. These examples 

 are the urea fermentation, the alcoholic fermentation, the 

 lactic fermentation and the vinegar fermentation. It 

 is assumed by most bacteriologists that all fermentations 

 are due to enzymes, though it seems to be extremely 

 difficult to bring about the experimental proof. 



The statement that fermentation is caused by enzymes, 

 means primarily only the achievement of a mechanical 

 separation of the cause of fermentation from the living 

 cell. Even under the most favorable circumstances, 

 this separation has been very incomplete. The cell 

 juice pressed out from yeast is quite weak in fermenting 

 power as compared with a corresponding volume of living 

 cells. The significance of the separation first accom- 

 plished by Buchner (1897) lies in the proof that the 

 energy-yielding processes are mere chemical processes. 



