72 OPT. AVTl 1 ., HEREDITY AM) EX 1 Ih'OXMEXT 



be followed in the cells of different organisms and then 

 the production of the right or the left isomer of lactic 

 acid by various types of bacteria or tissues would be 

 accounted for. A physiological mutation which brings 

 about an optical inversion of the secondary protoplasmic 

 constituents may consequently consist in a change of the 

 intermediate pathways in the transformation of these 

 substances. 



It appears then that the right and the left form of a 

 substance should not be considered so fundamentally op- 

 posed as far as their production is concerned, since one 

 has only to change the path followed in the transforma- 

 tions to obtain one or the other. 



What happens when a right or left isomer originates 

 might also happen when the relative configuration of 

 optically active organic substances is concerned. In the 

 majority of cases optical isomers entering into the com- 

 position of living systems possess the same relative con- 

 figuration. Thus the configuration of natural alanine is 

 the same as that of natural ephedrine (Freudenberg and 

 Nikolai, 1934) ; the configuration of natural proline is the 

 same as that of natural nicotine according to Karrer 

 (see Pfeilfer and Christeleit, 1937). But there are also 

 cases in which the substances which constitute living sys- 

 tems belong to different series. Thus dextrorotatory lac^ 

 tic acid, which is so generally found in the tissues of 

 higher animals, possesses the same relative configuration 

 as the unnatural laevorotatory tartaric acid, which is 

 never found in organic material. (It also has the same 

 configuration as natural dextrorotatory alanine; cf. 

 Freudenberg and Rhino, 1924, and Freudenberg, Brauns 

 and Siegel, 1923). The unity or the diversity of the rel- 

 ative configuration of organic substances, as well as the 

 character of being dextro- or laevorotatory, might depend 

 onl}^ on the biochemical path followed in the formation 

 of the substance. 



