74 OPT. A CTIV., HEREDITY AND ENVIRONMENT 



formation of the left lactic acid, the structurally inactive 

 methyl-glyoxal represents an intermediate stage and, 

 according to Embden's scheme, in the formation of dex- 

 trorotatory lactic acid, the structurally inactive pyruvic 

 acid is the intermediate stage. The dissymmetric con- 

 figuration of the molecules is believed to disappear in the 

 intermediate stages of transformation and then to re- 

 appear again. In this interpretation one assumes that 

 the asymmetry of molecular aggregates has disappeared 

 in the intermediate stages because of the loss of dis- 

 symmetry of the molecules. 



However, it is not necessarily so and Neuberg (1913), 

 questioning such intermediate loss of dissymmetry, 

 brought forward the theory of ''temporary dissymmetric 

 substances." If, for instance, in the intermediate stages 

 of transformation, methyl-glyoxal possesses some H and 

 OH groups attached to it, the dissymmetric configuration 

 of molecules will not disappear nor the asymmetric struc- 

 ture of molecular aggregates; then it would be possible 

 that in the production of one of the two optical isomers 

 of lactic acid from an initial active glucose by one type of 

 microbes a Walden inversion of the configuration of mole- 

 cules takes place. 



The various questions studied in the last two sections 

 suggest the two following generalizations which may be 

 of significance in understanding the basic principles of 

 vital activity : 1 . The impossibility of altering the optical 

 properties of the primary substances of protoplasm fits in 

 with the assumption that the activity of the fundamental 

 physiological systems is based upon the principles of 

 ''fixed pathway", i. e., all the intermediate transforma- 

 tions in these physiological systems would proceed along 

 definitely fixed paths. On the contrary, the optical prop- 

 erties of the secondary protoplasmic substances can be 

 altered to a certain extent. Consequently, the formation 

 and the transformations of the secondary substances are 

 not bound by the principles of fixed pathway. 2. Fur- 



