OPT. ACTIY., HEREDITY AXD ENVIRONMENT 71 



so much investigated of the production of one optical 

 form of hictic acid by one kind of organism and of the 

 production of the other isomer of lactic acid by other 

 organisms. 



An important contribution to the study of this phe- 

 nomenon has been brought forward by Embden, Baldes 

 and Schmitz (1912) who discovered that in the transfor- 

 mation of glucose into lactic acid by different animal tis- 

 sues dextrorotatory lactic acid is produced exclusively. 



Another important advance was the finding of Neuberg 

 (1913) that extracts of animal tissues transform ethyl- 

 glyoxal, a structurally inactive body, into laevorotatory 

 lactic acid. A number of papers were then published on 

 the methyl-glyoxal reactions. It was found that in all 

 cases when methyl-glyoxal is converted into optically ac- 

 tive lactic acid the latter is laevorotatory. This was ob- 

 served, in particular by Neuberg and Kobel (1927) with 

 the yeast, Sacfiharomyces cerevisiae, by Neuberg and 

 Simon (1928) with Mucor javanicus and by Widmann 

 (1929) with Bacterium fluorescens. 



From these observations Embden, Deuticke and Kraft 

 (1933) drew the important conclusion that since in tis- 

 sues of higher animals pure dextrorotatory lactic acid is 

 always formed and since the same tissues transform 

 methyl-glyoxal into laevorotatory lactic acid, methyl- 

 glyoxal cannot be the precursor of the dextrorotatory 

 lactic acid which appears in normal metabolism. Embden 

 then developed his theory of glycolysis in muscle which 

 received general acknowledgment. But, so far as we are 

 concerned in the present review, the essential fact is that 

 both optical isomers of a certain substance can appear in 

 metabolism when different intermediate substances are 

 involved. The left isomer of lactic acid is obtained 

 from glucose if the intermediate is methyl-glyoxal, and 

 the right isomer of lactic acid if the intermediate is, 

 according to current views, pyruvic acid. Embden sug- 

 gested that one or the other of these ^'pathways" could 



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