ON BACTERIOLOGY IN ITS KELATIONS TO CHEMICAL SCIENCE. 449 



only are converted into COOH, the resulting lactic acid will Lave its 

 asymmetric carbon atom, with the sign + before it. It is unnecessary 

 to point out that all these signs may also be directly opposite to the 

 actually observed rotation, so that the speculation may be more correctly 

 and briefly summarised in the words, that wJiilst loth active lactic acids 

 are theoretically ohtainaUe hy the simplest decomposition of dextrose, only 

 one arid the same of the ttvo active isomers should he similarly obtainabte 

 from either Icevulose or mannitol. 



On the other hand, it is equally obvious that in order to obtain inactive 

 lactic acid from any of the above molecules it is necessary either that 

 there should be an intermediate product formed in which the asymmetric 

 carbon atom of the ultimate lactic acid has lost its asymmetry, or that the 

 two active lactic acids should be formed in exactly equal molecular pro- 

 portions, and thus destroy the rotatory power. On the latter supposi- 

 tion, inactive lactic acid should only be readily obtainable from dextrose, 

 as neither the laBvulose nor the mannitol molecules are theoretically 

 capable of yielding, ly simple conversion, more than one of the isomeric 

 active lactic acids, but it is experimentally certain that inactive lactic 

 acid can be obtained by the fermentation of pure mannitol. 



In these decompositions effected by micro-organisms a remarkable 

 feature is not unfrequently observed which must be of great significance, 

 both from a chemical and biological point of view— I refer to the pheno- 

 menon of selective or preference fermentation. This phenomenon was first 

 observed by Pasteur (' Jahresbericht d. Chem.,' 1860, p. 250 ; ' Comptes 

 Rendus,' xlvi.p. 615) in the case of tartaric acid,who found that both bacteria 

 and moulds attacked the dextro-rotary modification by preference ; simi- 

 larly, Lewkowitsch ('Berlin. Berichte,' 1883, pp.1568, 2722) found that in 

 the case of mandelic acid the Itevo-rotary isomer is first destroyed by the 

 mould Fenicillium glaucum. More recently I have shown that by the 

 fermentative action of the Bacillus ethaceticus on glyceric acid the Isevo- 

 rotary acid is first decomposed, obtaining in this manner a dextro-rotary 

 glyceric acid, which is of particular interest and value, inasmuch as it is 

 the simplest active acid which can be obtained in practically unlimited 

 quantity, and by means of which the laws regulating the rotatory power of 

 active bodies in general can be investigated in their simplest form. Of 

 this new substance no less than twenty active derivatives have already 

 been prepared in my laboratory, and have served to throw light on the 

 more recent speculations concerning the peculiarly fascinating subject of 

 the asymmetric carbon atom. Still more recently I have obtained by 

 this selective fermentation the dextro-rotary lactic or sarcolactic acid, 

 which, although long known, has hitherto been only obtainable with great 

 difficulty. I hope, however, by this means to render it as accessible as 

 the dextro-rotary glyceric acid, and the study of its derivatives, which are 

 as yet almost wholly unexplored, should also furnish important data for 

 stereo-chemical theory. 



The cause of this remarkable phenomenon of selective fermentation is 

 at present wholly wrapped in obscurity, but I would venture to suggest 

 that it is to be sought for in the differences which such optical isomers 

 only unfold when they are combined with other active bodies. Thus, 

 when the optically isomeric tartaric acids are combined with the optically 

 active base cinchonine, for instance, the resulting cinchonine dextro- and 

 laevo-tartrate exhibit marked differences of solubility from each other. Is 

 it not highly probable that optically active substances which are invariably 



1893. Q Q 



