462 LACTIC ACID 



These authors also look upon the route from glucose through 

 lactic acid to glyceric acid and glycolaldehyde as the prin- 

 cipal mode of carbohydrate catabolism in active metabolism 

 of the animal economy. 



Racemic Acid as an Intermediate Product. While Par- 

 nas and Bar are willing to accept the formation of racemic 

 acid as at most a by-path in the formation of lactic acid, 

 Embden regards it as the normal catabolic product of lactic 

 acid and as an intermediate product of the transition of 

 alanin into lactic acid and vice versa; a view which is in 

 harmony with the assumption of 0. Neubauer that catabol- 

 ism of a-aminoacids takes place through a-ketonic acids. 



Paul Mayer, 2B in Neuberg's laboratory, has seen after 

 administration of racemic acid to rabbits both lactic acid and 

 sugar in the urine. It might well be conceived, therefore, 

 that the route from glucose, through lactic acid, to racemic 

 acid may also be traversed in the reverse way : 



Sugar ^r** Lactic Acid ^""^Racemic Acid. 



Finally it should be noted that the route indicated in 

 Embden 's schema : 



Glucose >Lactic Acid >-Racemic Acid >-Acetaldehyde >-Diacetic Acid 28 



is possibly the one, too, which may be taken by the carbo- 

 hydrates in the synthetic production of higher fatty acids 

 in the body. Possibly this line of thought may prove fruitful 

 also in clearing up the mysterious processes of fat formation 

 in the economy. 



Appearance of Lactic Acid in the Urine. What do we 

 know, finally, of the excretion conditions of lactic acid? Small 

 amounts are always present in the blood. 27 In rabbits, in- 



25 P. Mayer (Neuberg's Lab.), Biochem. Zeitschr., 40, 441, 1912. 

 20 According to Neuberg (Berliner physiol. Gesel., 1912) racemic acid is 

 fermented by yeast very readily into acetaldehyde and carbonic acid: 



CH, 

 CH,.CO.COOH=C0 2 + I 



27 A. Fries (G. Embden's Lab.), Biochem. Zeitschr., 35, 368, 1911. 



