232 OPTICALLY ACTIVE FERMENTATION PRODUCTS. 



which account the two optically active modifications can be sepa- 

 rated without much difficulty. Thus, it was shown by T. PURDIE 

 and J. W. WALKER (I.) in 1892, that by combining the optically 

 inactive "fermentation lactic acid" with strychnine, it can be 

 decomposed into its two optical components, viz., dextro-rotatory 

 sarcolactic acid and levo-rotatory lactic acid. 



However, the most important method of separation is that in 

 which the activity of micro-organisms is called into play. This 

 method, also, was proposed by Pasteur in 1860. He sowed certain 

 lower fungi the precise species cannot now be ascertained in a 

 solution of optically inactive ammonium racemate, and found that 

 the levo-rotatory properties of the liquid gradually increased ; and 

 that after a certain lapse of time ammonium levo-tartrate alone was 

 detectable. It must therefore be concluded that certain ferments 

 are endowed with selective powers. In the present instance, the 

 organism has separated the racemic acid into its two optically 

 active components, one of which (the D-tartaric acid) it consumes, 

 whilst the other (the L-acid) is liberated. Since Pasteur's time 

 this separating power has been utilised in various ways, two 

 examples of which are now given. In the first place, J. LEW- 

 KOWITSCH (I.) in 1882 dissociated the optically inactive mandelic 

 acid, C 6 H 5 CH.OH COOH, into its two active components in 

 this manner. On the other hand, P. FRANKLAND and W. FREW 

 (III.) allowed their Bacillus ethaceticus to react on the calcium 

 salt of the optically inactive glyceric acid 



CH 2 OH CH.OH COOH, 



whereby its dextro-rotatory component was obtained, the levo- 

 component being consumed. 



140. The Production of the Stereoisomerie 

 Lactic Acids 



by fermentation merits closer attention. In the first place, it 

 should be mentioned that only the three isomers of ethylidene 

 lactic acid, CH 3 CH.OH COOH, are in question, since ethylene 

 lactic acid, CH 2 .OH CH 2 COOH, has hitherto been obtained 

 by purely chemical means alone. The sub-title, fermentation 

 lactic acid, so long borne solely by the inactive form of ethylidene 

 lactic acid, is now recognised as also appertaining to both its stereo- 

 isomers, so that the term is now synonymous with ethylidene lactic 

 acid generally. Of the two active forms, the so-called paralactic 

 acid was the first to be prepared by the fermentation method, the 

 discovery being due to M. VON NENCKI and N. SIEBER (I.) in 1889. 

 These observers found that certain tumours in an animal affected 

 with symptomatic anthrax contained (in addition to the charac- 

 teristic bacillus of this disease) an anaerobic fission fungus, which 

 produces large quantities of paralactic acid (i.e. dextro-lactic acid) 



