CARBOHYDRATES. 15 



before this Adolf v. Baeyer * had explained in exactly the same way the 

 formation of carbohydrates in plants. According to this conception, which 

 up to the present time has not been proved absolutely, the leaves contain- 

 ing chlorophyll reduce the carbon dioxide of the air to formaldehyde, and 

 the latter is transformed into sugar by condensation. The formation of 

 sugars containing a different number of carbon atoms can be similarly 

 explained with the help of the same hypothesis. It is, indeed, perfectly 

 possible that the building up of the higher sugars by nature takes place 

 through the same intermediate stages as have been observed in the arti- 

 ficial synthesis. 



Now, an accurate examination showed that the sugar obtained from 

 glycerose, or from formaldehyde, containing six atoms of carbon was not 

 identical in all its properties with grape-sugar. It was, therefore, given 

 a special name, acrose. Biot 2 made the important discovery that cane- 

 sugar rotates the plane of polarized light. This property, which other 

 sugars found in nature likewise show, was quickly utilized technically 

 for the quantitative determination of cane-sugar in cane-juice, etc. 3 It 

 proved to be also of considerable aid in distinguishing the different 

 kinds of sugar from one another. Now acrose does not have this property : 

 it does not rotate the plane of polarized light. The reason for this is that 

 acrose is composed of components each having the opposite effect upon 

 polarized light, and as a matter of fact it is possible to decompose acrose 

 into these unlike individuals. According to the conditions of the experi- 

 ment, it may be changed into fruit-sugar or mannose or grape-sugar. 

 Herewith the final step in the artificial synthesis of sugars such as occur 

 in nature was accomplished. 



The optical activity of almost all natural products a property which for 

 a long time served to distinguish natural products sharply from artificial 

 ones, and gave support to the theory that a special force peculiar to a living 

 organism was necessary for the production of such compounds, until at last 

 here also successful synthetical chemistry made a breach in the wall which 

 had been considered as impregnable was first explained by the well-known 

 fruitful hypothesis of Le Bel and van 't Hoff 4 (1874). These two scien- 

 tists independently traced the asymmetry of the molecule, which Pasteur 5 



1 Ber. 3, 63 (1870). 



2 Compt. rend. 10, 264; 16, 619 (1843). 



3 Clerget: Compt. rend. 16, 1000 (1843); 22, 1138 (1846); 23, 256 (1846); 26, 240 

 (1848). 



4 Cf. van't Hoff: Die Lagerung der Atome im Raume. Dix anne*e dans Thistoire 

 d'une throne. La chimie dans 1'espace (1875). K. Auwers: Die Entwicklung der 

 Stereochemie (1890). 



5 Lecons de chimie professes en 1860. Paris, 1861. See also H. Landolt: Das optische 

 Drehungsvermogen organischer Substanzen und dessen praktische Anwendungen, 

 Braunschweig, 1898. A. Werner: Lehrbuch der Stereochemie, Jena, 1904. 



