ENERGY TRANSFORMATION 413 



The heat liberated in the fermentation reactions is calculated as follows: 



Heat of combustion of glucose 674.0 Cal. 



Heat of combustion of alcohol 326.2 Cal. 



Pleat of solution of glucose 2.1 Cal. 



Heat of solution of alcohol 2.25 Cal. 



(674 + 2.1) - 2(326.2 - 2.25) = 28.2 Cal. 

 glucose alcohol 



Since in the reaction of alcoholic fermentation, some other reaction products are 

 formed, the amount of heat produced by a mol of sugar converted into alcohol 

 is about 27 cal. Rubner found that actually 24 cal. were liberated in this re- 

 action. 



Some of the anaerobic fermentations are not accompanied by the 

 production of CO2, as in the lactic and acetic acid fermentations. 



C 6 H12 Oe = 3 CH 3 COOH + 44 Cal. 



In the anaerobic decomposition of cellulose, whereby hydrogen and 

 methane are formed (whether by pure cultures or mixed cultures) 

 the following reactions may be suggested: 



3 C 6 H 12 6 = 3 CH 3 • CH 2 • CH 2 • COOH + CH 3 • COOH + 4 C0 2 +2 H 2 + 2 H 2 

 butyric acid acetic acid 



3 C 6 H 12 6 = 2 CH 3 • CH 2 • CH 2 • COOH + 2 CH 3 • COOH + 4 C0 2 + 2 H 2 + 2 CH 4 



When the heat of reaction of oxidation is compared with that of 

 "fermentation," the former is found to be much greater than the latter: 

 1 mol of sugar liberates 676 Cal. when it is completely oxidized (to C0 2 

 and H 2 0) and only about 25 Cal. in the alcoholic or lactic acid "fer- 

 mentation," and even less in the butyric acid fermentation. Since 

 the amount of growth of the cells of microorganisms is in direct pro- 

 portion to the production of energy, much larger quantities of sub- 

 strate have to be decomposed in the "fermentations" than in the oxi- 

 dations by free oxygen in order to liberate the same amount of heat 

 and allow the same amount of work or equal growth of the cells to 

 take place. Some of the products of the "fermentation" processes 

 may be used for the synthesis of the cellular substance. This is par- 

 ticularly true in the decomposition of proteins and carbohydrates. 58 



When organic acids, hydrogen and methane are the products of 

 decomposition they may be used as sources of energy by other micro- 



68 See Meyerhof, O. Uber den Einflusz des Sauerstoffs auf die alkoholische 

 Giirung der Hefe. Biochem. Ztschr., 162: 43-86. 1925. 



