448 



BEPORT 1893. 



moulds when growing superficially on organic liquids is, so far as we 

 know, entirely different from that of bacteria, inasmuch as the moulds 

 simply convert the organic elements into their ultimate products of oxida- 

 tion, and do not excite fermentations in the stricter sense of the word. 



Becent Additions to Knowledge of Lactic Fermentation. — The lactic 

 fermentation, which was one of the earliest-known fermentations, and 

 with the investigation of which the names of Pasteur and Lister are 

 associated, has recently formed the subject of some researches, which 

 appear to me to be of particular interest from a chemical point of view. 

 In the ordinary lactic fermentation, as is well known, the lactic acid 

 obtained is inactive, irrespectively of whether it is derived from starch, 

 milk-sugar, cane-sugar, dextrose, or mannitol. By employing different 

 lactic fermentation bacteria, however, both the active lactic acids have 

 been obtained by direct fermentation. Thus Nencki and Sieber ('Berlin. 

 Berichte,' xxii. c. 695) have discovered a lactic ferment which yields sarco- 

 lactic acid {i.e., dextro-rotary lactic acid) in the fermentation of dextrose ; 

 whilst Schardinger (' Chem. Soc. Journ.,' Abstr., 1891, p. QQQ) has de- 

 scribed the production of lasvo-rotary lactic acid in the fermentation of cane- 

 sugar. How are these three different lactic fermentations to be interpreted 

 by the light of our present knowledge of the constitution of the sugar 

 molecules, which is based on those researches of Emil Fischer, which 

 have excited such profound and widespread admiration ? 



Taking the now generally accepted constitutional formulse of dextrose, 

 Isevulose, and mannitol — 



CH.,OH CH..OH CH.,OH 



Dextrose 



in which the several asymmetric carbon atoms are indicated by the signs 

 + or — according to the relative arrangement of the groups around 

 them. It is easy to see how the carbon-skeleton of dextrose can yield by 

 simple decompositions, in which the terminal groups — COH or CH.2OH — 

 are converted into COOH, either the dextro- or the Isevo-rotary lactic 

 acid, according to the particular asymmetric carbon atom in the dextrose 

 which is made to form the asymmetric carbon atom in the lactic acid, 

 thus : — 



CH3 CH3 



-CHOH 



+ CHOH 



COOH 

 Ljevo-rotary 

 lactic acid. 



COOH 



Dextro-rotary 

 lactic acid. 



Again, by such simple decomposition, the laevulose molecule should 

 only be capable of yielding the dextro-rotary lactic acid ; and similarly 

 the mannitol molecule should only be capable of yielding the dextro- 

 rotary lactic acid ; for it is obvious, again, that, if the terminal groups 



