August 6, 1896J 



NA TURE 



left-handed molecules, CR'R-R'R^, act difterently, we 

 may conclude that this substance contains molecules 

 which are themselves asymmetric. So that when we 

 find, for example, a certain species of microscopic 

 organism fermenting and destroying a "right-handed" 

 sugar, but not attacking a " left-handed " sugar otherwise 

 identical with the first, we may conclude that those 

 molecules of the ferment which are concerned in the 

 attack are themselves, all or some of them, of a decidedly 

 right- or left-handed character. The line joining their 

 atoms would itself be a spiral, the thread of a screw. 

 And in fact we find living organisms to be largely com- 

 posed of asymmetric molecules, albuminoids, which 

 themselves e.xert a one-sided action on light. 



It is evident, then, that there is a relation between a 

 ferment and the substance it ferments, as between a solid 

 screw and a hollow screw with threads which enable one 

 to turn in the other. 



And the recent researches of Fischer and Thierfelder 

 show the relation between every turn of the two threads 

 to be most intimate. In these experiments, twelve 

 diflerent species of yeast were obtained pure and free 

 from other organisms, and fourteen different sugars were 

 tested with each species of yeast. After eight days it 

 was found that some of the sugars were completely 

 fermented, some only partially, some not at all. 

 And it was observed that the same ferment would attack 

 sugars of widely varying composition, a sugar containing 

 only three carbon atoms, e.g., as readily as one with nine 

 carbon atoms in its molecule. But directly it became a 

 question of the geometrical structure of the sugar mole- 

 cule the ferments showed the nicest particularity. In the 

 case of sugars containing six carbon atoms and of exactly 

 the same chemical composition, some would ferment 

 readily, and others not at all. 



For example, there were tested : 



Dextro-glucos) 



HCOH 



I 

 HCOH 



I 

 HCOH 



H 



O 



I 



H 



■gala 

 O 



V 



H 



O,, 



.H 



HOCH 



I 

 HOCH 

 I 

 HCOH 



I 

 HCOH 



I 



HCOH 



H 



I 

 HCOH 



HOCH 



I 

 HOCH 

 1 

 HCOH 



I 

 HCOH 

 H 



HOCH 



I 

 HOCH 



I 

 HOCH 



I 

 HCOH 



I 

 HCOH 



H 



In each of these four molecules the atoms are the same 

 in kind and in number. The only difiference is that 

 whereas in I. there is on one side of the molecule — say 

 on the left, as in the formula given — only one OH group, 

 in II. there are two OH groups on the left, in III. also 

 two, but not the same two, and in IV'. there are three. 

 Now it is found that, with the same yeast-species. III. 

 ferments with more difficulty than either I. or II., and 

 the slight further change in the space-relations suffices 

 to deprive I\'. altogether of the power of fermenting. 

 This is but one example of the way in which the yeast- 

 cells pick and choose their food. Here, as Fischer 

 observes, we have not simply to do with two similar 

 substances of opposite activity — represented by screws 

 having threads opposed throughout — but we find that 

 of a great number of geometrical forms only a few 

 satisfy the requirements of the yeast-cells ; and these 

 few forms are represented by screws in which the threads 

 differ only as regards the direction of one or two of their 

 turns. This may be illustrated by the figures below ; 

 for although it is impossible to give an exact representa- 

 tion of the geometrical forms of the molecules of the 

 sugars in question, if is certain that the relations between 



their forms must correspond to the relations between the 

 figures given, which are formed by a line starting from 

 the COH group {a\ joining C, OH, and H, always in 

 the order named, and ending at the group CH^GH {B). 

 If the zig-zag thus obtained be considered as the thread 

 of a screw, it will be seen that in I. (Fig. 5) the thread is 

 reversed at C- and again at C^ In II. (Fig. 6), which 

 also ferments readily, there is reversal at C-* only, in 



HO^r-"-^' 



a 



Fig. 7. Fig. 8. 



III. (Fig. 7), which ferments with difficulty, at C- and 

 C, and in IV. (Fig. 8), which ferments not at all, at 

 C* only. 



These relations are shown yet more clearly in the 

 following figures, in which the side of the OH group is 

 represented by a broad curve, while the sharp angle is 

 retained for the H side. 



^B 



^B 



In the fermentation of all the sugars, the chief agent 

 is, according to Fischer, proteid matter, a substance 

 which is itself asymmetric, and which, being formed from 

 the carbohydrates of plants, probably possesses a geo- 

 metrical structure similar to that of the natural six-carbon 

 sugars. Hence it can attack and ferment substances 

 geometrically not far removed from these, i.e. from grape 



NO. 1397, VOL. 54] 



