THE VITAL PHENOMENA OF BACTERIA. IOI 



merits of the atoms in the several molecules 

 only becomes manifest through the behavior of 

 the substance in fermentation. 



In order to construct a molecule of given con- 

 stitution, however, differing amounts of energy, 

 dynamically considered, must be expended ac- 

 cording as the union of atoms be strong or 

 feeble ; and correlatively, this union of atoms 

 can according to its firmness with greater or 

 less ease be loosed again. If we consider two 

 sugars of the same group and similar empirical 

 composition, such for example as the hexoses 

 or sugars containing six atoms of carbon, all 

 of which have the same empirical formula 

 C G H 12 O 6 , we can distinguish these as aldehyde 

 sugars or aldoses (with the group COH), and 

 as ketone sugars or ketoses (with the group 

 CO). Thus, for example, grape-sugar, an 

 aldose, possesses the formula CH 2 (OH). 

 (CHOH) 4 .COH, while fruit-sugar, a ketose, 

 has the formula CH 2 (OH).(CHOH) 3 CO.CH 2 

 OH. If we experiment with two such alde- 

 hyde sugars in which the inner stability of the 

 molecule depends upon the opposite positions 

 of certain atom groups, as is seen in grape- 

 sugar and galactose, we find that the compara- 

 tively unstable grape-sugar possesses, accord- 

 ing to Stohmann, a greater store of energy 

 than the more stable galactose ; consequently 



