orr. ACT I v.. in:in:niTY \\i) r:\]Jh'o\]iE\T 61 



cannot be directly involved in nietabolisiii. I'lie slight 

 growth observed on aniino-acids which can be deaminated 

 and thus transformed into material deprived of dissym- 

 metry, from which subsequently molecules of suitable 

 properties are built, even confirms this view. This con- 

 clusion is in accord with a number of recent observations 

 (Conrad and Berg, 1937; Du Vigneaud et al., 1939; Rat- 

 ner, Schoenheimer and Eittenberg, 1940). 



2. The ImpossihUity of Modifying Protoplasm so as 

 to Cause it to Invert the Optical Properties of the Prod- 

 ucts of its Metabolism. That some products of meta- 

 bolism, that is, some secondary constituents of living mat- 

 ter may be generated in either of the two optically 

 isomeric forms, under the influence of external conditions, 

 has been admitted for a long time by a number of inves- 

 tigators. The case of lactic acid fermentation by some 

 microbes is classical in this respect. Concerning this 

 case we shall mention first the fundamental facts on the 

 specificity of each bacterial strain in the production 

 of one type of lactic acid and then we shall review the 

 more important investigations on the effect of external 

 conditions on such production. 



Nencki (1891) showed that the optical form of the lac- 

 tic acid i^roduced in microbial fermentation is specific 

 for the kind and strain of microbes. Some species pro- 

 duce the pure dextrorotatory isomer, others give the 

 pure laevorotatory one and still others produce a form 

 of lactic acid which is either totally or partially racemic. 

 The sign of the asymmetry of the secondary substances 

 seems, therefore, to represent a stable hereditary char- 

 acteristic of the physiological organization of the cell 

 which has produced these substances and Nencki even 

 proposed to employ it for the identification of bacteria. 

 These observations were subsequently confirmed by Cur- 

 rie (1911), Pederson, Peterson and Fred (1926) and by 

 Katagiri and Kitahara (1937). 



