SUGAR AND LACTIC ACID 461 



lactic acid is based on the fact that it (in contrast to the 



CH.OH 



isomeric dioxy acetone, CO , which according to Buchner 



CH,.OH 



and Meisenheimer is an intermediate product of yeast 

 fermentation) has proved to be a lactic acid producer of very 

 exceptional strength. Embden suspects that, just as gly- 

 cerolaldehyde is an important source for 8-lactic acid, di- 

 oxyacetone may be considered as the chief source of inactive 

 fermentative lactic acid, and expresses the idea that in tran- 

 sition of the glycerolaldehyde into lactic acid 

 CH 2 .OH CH, 



"CH.OH > * CH.OH 

 COH COOH 



the middle carbon atom continues to retain its asymmetrical 

 character. 



The belief that glycerol formation in the economy also 

 proceeds through the intermediate stage of glycerolaldehyde, 

 and that by this route sugar may pass into glycerol, and, 

 vice versa, glycerol into sugar, is not incredible. 



It may be thought, too, that not only does sugar undergo 

 transition into lactic acid, but that the reverse, the transition 

 of lactic acid into sugar, is also possible. Embden and Salo- 

 mon 22 have convinced themselves that lactic acid is a sugar 

 former in depancreatized dogs ; Mandel and Graham Lusk, 23 

 in phloridzinized animals. 



According to Parnas and Bar 24 the route from lactic acid 

 to glucose leads through glyceric acid and glycolaldehyde : 



LACTIC ACID . GLYCERIC ACID GLYCOLALDEHYDE GLUCOSE 



CH, CH 2 OH CH 2 .OH > CH 12 O. 



> > I Condensation 



CH.OH Oxidation CH.OH Oxidation, COH 



Cleavage of 



COOH COOH HO* and CO* 



22 G. Embden and Salomon, Hofmeister's Beitr., 5, 507, 1904 



23 A. Mandel and G. Lusk, Amer. Jour, of Physiol., 16, 129, 1906. 



24 Cf. also J. Parnas and J. Bar (Hofmeister's Lab., Strassburg), Biochem. 

 Zeitschr., 41, 386, 1912. 



