102 BACTERIOLOGY. 



less energy is needed to topple over the mole- 

 cule of grape-sugar than the molecule of galac- 

 tose. Grape-sugar, also, according to experi- 

 ments which I have made, is more easily fer- 

 mentable by yeasts than galactose, so that 

 here also a choice of food-material occurs, the 

 physical reason for which can be foreseen in 

 the structure of the molecule. The same thing 

 is true also among the so-called ketone sugars 

 or ketoses ; among the hexoses belonging to 

 this group, the more unstable fruit-sugar pos- 

 sesses a greater store of energy than the more 

 stable sorbinose (Stohmann). The former is 

 easily fermentable, the latter difficultly so. 

 E. Fischer and H. Thierf elder l have lately for- 

 mulated this principle anew and have ex- 

 tended its application to several new kinds of 

 sugars. 



The celebrated investigations of E. Fischer 2 

 upon the so-called constitution or atomic struc- 

 ture of the sugar molecule require, then, for 

 -their full comprehension to be supplemented by 

 Stohmann's investigations on the dynamic or 

 energetical relations of the same molecule, and 

 also by the biological facts which were first 

 established by Pasteur. With knowledge of 



1 Ber. d. Deutsch. Chem. Gesellsch., XXVII., 1894, p. 2031. 



2 Ber. d. Deutsch. Chem. Gesellsch., XXIII., 1890, p. 2114, XXVI., 

 1894, p. 3189- 



