470 LECTURE XX. 



One of the most interesting properties of the ferments is their specific 

 action. The animal, and also the plant organism, as we have mentioned 

 many times, works almost exclusively with optically active carbon com- 

 pounds, i.e., with compounds which have at least one asymmetric carbon 

 atom. The asymmetry of the elementary constituents of the cells begins 

 at the moment of the assimilation of carbon-dioxide 1 by the parts of the 

 plants containing chromophyll, and is transferred directly by the herbivora, 

 indirectly by the carnivora, into the animal organism. From a compound 

 containing only one asymmetric carbon atom we can imagine two optical 

 isomers and one racemic compound formed by a union of the two. 2 Even 

 Pasteur 3 was acquainted with the fact that if we inoculate a solution of 

 ammonium tartrate, containing a small amount of nutrient salts, with 

 traces of Penicillium glaucum, a peculiar change takes place. The solu- 

 tion, which was at first entirely inactive, becomes optically active during 

 the development of this mold, rotating towards the left. The laevo- 

 rotation continues to increase, and only assumes a constant value when 

 the dextrotartaric acid, the optical isomer of the laevotartaric acid, has 

 been entirely consumed by the mold. This interesting phenomenon can 

 be explained on the assumption that the mold evidently only utilizes one 

 of the optical modifications of tartaric acid, while laevotartaric acid remains 

 unchanged. After this observation of Pasteur, which was attributed to 

 the action of an organized ferment, others followed. Thus, by the aid of 

 Penicillium glaucum, the following optically active forms were obtained from 

 the racemic compounds: d-mandelic acid, d-aspartic acid, d-leucine, Z-tartaric 

 acid, Z-mannonic acid lactone, Z-glutamic acid, and Z-glyceric acid. 4 



Felix Ehrlich 5 has made an interesting discovery in this direction. He 

 permitted a pure culture yeast to act upon synthetically prepared, racemic 

 leucine, in the presence of cane-sugar. After a time a distinct odor of 

 fusel oil was noticed. Isoamyl alcohol was separated from the liquid by 

 fractional distillation. All the leucine present was not used up in this pro- 

 cess, but only the Z-leucine. The d-leucine could be recovered unchanged 

 from the liquid. The same experiment, using d-isoleucine, resulted in the 

 formation of d-amyl alcohol. The splitting of racemic bodies into the 

 optically active components by means of lower organisms has become an 

 important method for the preparation of such compounds, and has become 

 of great significance in identifying synthetically produced substances 

 with those which occur naturally. As different organisms decompose 

 different parts of the racemic bodies, it is possible for us to obtain in this 



1 Compare Lecture IV, p. 54. 



2 Compare Lecture II, p. 15. 



3 Compt. rend. 51, 298 (1860). 



4 Compare C. Winther: Ber. 28, 3000 (1895). 



5 Z. Vereines Deut. Zuckerind. 56, 592 (1905X 



