450 REPORT— 1893. 



present in living cells may enter into combination with these optically 

 active fermentable isomers, and by thus establishing differences — e.g., of 

 solubility — between them render one of them — probably the more soluble 

 one — more accessible to the specific decomposing influence of the cell- 

 protoplasm ? 



Whether in such selective fermentations it is invariably the same 

 optical isomer or not that first disappears under the influence of vital de- 

 composition has not been with certainty ascertained. Pasteur, however, 

 found that it was the dextro-tartaric acid which was first destroyed, 

 irrespectively of whether a bacterial fermentation or a mould combustion 

 was employed. Similarly, in the case of lactic acid, it was the laevo-rotary 

 acid which first disappeared in my bacterial fermentation, already referred 

 to, as well as in the mould combustion of lactic acid, studied by Linossier 

 ('Berlin. Berichte,' xxiv. c. 6G0). On the other hand, Lewkowitsch (loc. 

 cit.) records the preferential decomposition of one optically isomeric man- 

 delic acid by the mould Penicillium glaucum, and of the opposite isomer by 

 a bacterial ferment. As this is, so far as I am aware, the only instance of 

 the kind, it is highly desirable that it should be reinvestigated, and either 

 confirmed or disproved. 



It must not be supposed that in this selective fermentation one of the 

 isomers is necessarily quite unfermentable, for, as far as this matter has 

 been carefully investigated, it would appear to be only that one of the 

 isomers is relatively less fermentable than the other. Thus in the 

 fermentation of lactic acid, which I have recently studied, I found that 

 if the fermentation was allowed to finish the whole of the lactic acid was 

 broken up into other products ; but if arrested at an intermediate stage 

 the lactic acid remaining undecomposed always contained sarcolactic 

 acid, showing that the laavo-rotary lactic acid had been decomposed by 

 preference. 



In the fermentation of glyceric acid the selective phenomena are 

 extremely remarkable. Thus when I first isolated the Bacillus ethaceticus 

 some years ago I found that its powers of fermenting glyceric acid in the 

 form of calcium glycerate were very feeble, and that even when the 

 fermentation was allowed to complete itself practically the whole of the 

 dextro-rotary glyceric acid remained untouched by the bacillus. But on 

 continuously cultivating this bacillus in solutions of calcium glycerate I 

 found that its power of decomposing this substance was becoming markedly 

 greater ; thus, not only did the fermentations last longer, but the propor- 

 tions of undecomposed dextro-rotary glyceric acid remaining at the end 

 of the fermentations became less and less. In order, therefore, to obtain 

 a satisfactory yield of the residual active glyceric acid, it now becomes 

 necessary to arrest the fermentation, and thus save the dextro-glyceric 

 acid from destruction. We can also still obtain a satisfactory yield of the 

 active glyceric acid by using for the fermentation ethacetic bacilli which 

 have hitherto been strangers to solutions of glyceric acid ; these bacilli 

 then only decompose the l^vo-glyceric acid, the dextro-glyceric acid 

 molecules being untouched by them. In fact, in this manner the 

 fermentative activity of this Bacillus ethaceticus can be regulated with 

 the greatest nicety and precision, and this forms a good example of the 

 profound modifications which can be eflected in micro-organisms by what 

 may be called educational culture. 



Modifications effected in Micro-organisms by Educational Culture. — 

 This subject of the modification of micro-organisms by artificial means is 



