ENERGY SUPPLY OF THE CELL 27 



difference between the potential energies (or combustion heats) of 

 sugar and alcohol. 



1 gm. molecule of glucose = 677.2 cal. 



2 gm. molecules of alcohol = 651.2 cal. 



26.0 cal. 



The difference of 26.0 cal. is all the energy liberated in the alcoholic 

 fermentation. It is only one-twenty-sixth of the amount obtained 

 by oxidation. This means that for the production of 3,739 cal., 

 the mold will need only 1 gm. of sugar if plenty of oxygen is available, 

 but that 26 gm. will be needed by yeast if no oxygen is available. 

 This is one of the reasons for the surprisingly great rate of decomposi- 

 tion of food by microorganisms. 



The equation of the alcoholic fermentation should be written more 

 completely and more correctly: 



CeHisOe = 2C2H5OH + 2CO2 + 26.0 calories 



But even that would not be really correct. If sugar is dissolved in 

 water, the temperature decreases, and 2.25 cal. are disappearing for 

 every gram molecule; if alcohol dissolves in water, heat is liberated 

 to the extent of 2.54 cal. per gram molecule. These corrections should 

 also be included in the above equation. 



Tangl and Rubner tried to get more accurate data by 

 measuring the amounts of energy liberated in the 

 cultures themselves. Tangl (1903) used the combustion 

 heat method, as shown in Table 6. A broth culture 

 was dried on standard cellulose blocks and its combustion 

 heat determined directly. Part of this culture was 

 filtered and treated in the same way. The difference of 

 solids gives the solids of the bacteria grown in this 

 culture; the difference of combustion heats gives the 

 potential energy or combustion heat of these bacteria. 

 The potential energy of the sterile medium is 4.39 cal. 

 for each gram of solids, which is very nearly that of the 

 bacteria themselves. In spite of this similarity in com- 



