470 THE AMERICAN NATURALIST. [Vor. XXXV. 
and water, though simpler than sugar, may be formed from 
sugar without free oxygen or with free oxygen in smaller 
proportions than 6:1. Complete oxidation (normal respiration) 
yields the largest amount of energy possible ; less profound 
changes yield less energy. Thus the decomposition of sugar 
by yeasts, according to the following reaction, which represents 
only in simplest terms the nature of the chemical changes, 
C&H ;206 = 2 C; Hg O + 2 CO, 
forming without oxygen two molecules of alcohol and two of 
carbon-dioxide from one molecule of sear yields only 67 
calories per gram-molecule.! 
The decomposition of one molecule of dextrose into one 
molecule of butyric acid, two of carbon-dioxide, and two of 
hydrogen, which is accomplished by a considerable number of 
species of bacteria, and may be represented by this reaction, 
C, H,,06 = C, Hy O, + 2 CO, + 2 H,, 
yields about 75 calories per gram-molecule.? 
Bacteria forming acetic acid, acting on dilute solutions of 
ethyl alcohol in the presence of free oxygen, partially oxidize 
the alcohol and decompose it into acetic acid and water, thus: 
C,H,O + O, = Ci H, O; T H20, 
liberating 125 calories;? but if the alcohol were completely 
oxidized, as in ordinary combustion, the reaction would be 
C,H4O = Y Cu L2 CO. + 3 H20, 
and the heat liberated would be nearly three times as much, 
about 325 calories per gram-molecule. 
In these figures we have indices of the relative values of 
complete and incomplete oxidations, and of oxidations and 
decompositions, as sources of energy in the form of heat. 
These figures are indices, to be trusted only so far as relative, 
not exactly proportional, values are concerned. The chemist 
can control all the conditions under which he makes a 
1 Rechenberg, Zoc. cit., p. 66. 2 Rechenberg, /oc. cit. 
i OF: 
3 Quoted from Berthelot in Biedermann’s Chemiker-Kalender in 1897, p. 193 
of the Beilage. 
