STEREO-CHEMISTRY AND PHYSIOLOGY 455 



that when moulds of various kinds were allowed to grow in a 

 racemic solution to which phosphates or other nutrient matter 

 had been added, the solution gradually became optically active, 

 an excess of one antipode being left. At one time it was 

 supposed that the mould was unable to attack one antipode, 

 and confined its destructive action entirely to the other; but 

 the work of Frankland and MacGregor, 1 and of McKenzie and 

 Harden, 2 showed this to be erroneous ; the mould destroys both 

 antipodes, but appears able to attack one much more rapidly 

 than the other. This difference in action must be due to the 

 difference in configuration between the two antipodes. Since 

 some moulds attack the dextro form while others destroy the 

 laevo variety, it is possible to obtain either the left-handed or 

 the right-handed form of a given body by utilising the appro- 

 priate mould. For instance, if we treat racemic mandelic acid 

 with the ferment Penicillium glaucum, an excess of dextro man- 

 delic acid results, while laevo mandelic is obtained by using 

 Saccharomyces cllipsoideus. Fischer and Thierfelder 3 have noted 

 another case of fermentation in which even a slight difference 

 in the configuration appears to exert a considerable influence. 

 They treated the dextro forms of glucose, mannose, galactose, 

 and talose with the same ferment, and found that while the first 

 two were easily fermented, galactose was attacked only with 

 difficulty, while talose was not affected. When we examine 

 the space formulae of the four bodies, a possible explanation of 

 this difference suggests itself: 



Glucose Mannose Galactose Talose 



CH,OH CH,OH CHoOH CH..OH 



HO.H HO.H HO.H HO.H 



HO.H HO.H H.OH H.OH 



H.OH H.OH H.OH H.OH 



HO.H H.OH HO.H H.OH 



CHO CHO CHO CHO 



Ferment easily. Fermentable Unfermented. 



Fischer supposes that ferment and sugar fit each other as a 

 key fits a lock ; so that certain " wards " of the sugar can be 

 reached only if the ferment has a configuration similar to that 

 of the sugar. If we symbolise part of the ferment in the same 

 way as the sugars, and represent by X the "ward" which 



1 Frankland and MacGregor, Jonrn. Chem. Soc, 63, 1034 (1893). 



2 McKenzie and Harden, Joiirn. Chem. Soc, 83, 424 (1903). 



3 Fischer and Thierfelder, Ber., 27, 2035 (1894). 



