224 



not only proved this fact beyond all doubt, but from E. Fischer's 

 work l ) on the selective fermentation of sugars under the action 

 of yeasts, it seemed to follow that the action of every living organism 

 corresponds to only a definite, very exclusive, special arrangement 

 of the atoms in the chemical molecules. 



However, in recent times serious doubt has arisen, as to whether 

 the specificity of the action of organisms, as brought to the fore 

 by Fischer, and illustrated by his often quoted simile of lock and 

 key, should really be maintained. The way for further investigations 

 should be left open, but at any rate it seems nearer to the truth 

 to suppose that only great differences in speed of activity take 

 place 2 ). Indeed, the experiments of Neuberg 3 ) on the action of 

 bacteria, and those of Pringsheim 4 ) on that of moulds on 

 racemoids, seem strongly to confirm this last view. 



That from a physiological point of view there are undeniable 

 differences in the behaviour of living organisms towards enantio- 

 morphously related substances with which they are brought into 

 contact, is proved quite conclusively, and the same is also the case 

 for the human organism. Thus Piutti 5 ) already many years ago 

 drew attention to the fact that of both the isomeric optically 

 active asparagines the one component is sweet, the other insipid; 

 and Menozzi and Appiani 6 ). found the same fact in the case 

 of ghitaminic acid. According to Fischer 7 ), l-valine is insipid or 

 weakly bitter, but d-valine is sweet, and the racemic compound also. 



d-Leucine has undeniably a sweet taste, while l-leucine is insipid 

 or weakly bitter; d-phenyl-alanine is very sweet, the other antipode, 

 however, only a little bitter. But such a contrast is not always 

 present: d- and l-alanine, for instance, possess the same taste. 



With intra-peritoneal injection of optically active acids, l-tartaric 

 acid appeared to be the most poisonous, while the ^-antipode 

 showed only half the toxic effect of the former, and racemic 



1 ) E. Fischer and collaborators, Ber. d. d. Chem. Ges., 27, 2031, 2985,3228, 

 3479, (1894); 28, 1429, 1508, 3031, (1895); Zeits. f. physiol. Chemie, 26, 60, (1898). 



2 ) K. Fa jans, Zeits. f. phys. Chemie, 73, 25; 75, 232, (1910). 



3 ) C. Neuberg, Biochem. Zeits., 18, 431, {1909). 



4 ) H. Pringsheim, Zeits. f. physiol. Chemie, 65, 96, (1910). 



5) A. Piutti, Compt. rend, de 1'Acad. d. Sc. Paris, 103, 134, (1886); L. 

 Pasteur, ibid., p. 138. 



6) A. Menozzi and G. Appiani, Atti R. Acad. Lincei, (5), 2, 77, 421, (1893). 



7) E. Fischer, Ber. d. d. Chem. Ges., 39, 2328, (1906). 



