SYNTHETIC WORK IN CARBOHYDRATES 341 



constituents, the right and the left acids. The right mannonic 

 acid yields, by reduction, the right mannose on the one hand, 

 while on the other, by heating with chinolin or pyridin, a mole- 

 cular change takes place, and the d-gluconic acid is obtained, 

 which yields the active glucose. Finally, the active glucose and 

 mannose, through their phenyl-glucosazones, may be converted 

 into the active fructose. Thus the problem of the synthesis of 

 the most important natural sugars has been accomplished. 

 J Sugar, as a class, is thus derived not only from sources 

 pertaining to the land and sea, but also, from the brief sketch 

 just drawn, from no less a source than man's intelligence. 



According to the earliest records, the sugar-cane, the main 

 source of the supply of saccharose, or cane sugar, was culti- 

 vated in India for food supply. The beet-sugar industry dates 

 from our own time. 



Cane sugar is found in many plant species, and occurs in 

 grain during germination at the expense of starch, as it was 

 observed in the barley. Cane sugar has not as yet been made 

 synthetically. It stands as one of the atomic peaks still to be 

 scaled. The discovery, by Biot, of the power of cane sugar 

 solutions to turn the plane of polarized light led Dubrunfaut, 

 in 1847, on decomposing cane sugar, to discover fructose, the 

 second sugar constituent of cane sugar. In the same way, we 

 may read any day the announcement of the discovery of a 

 chemical spyglass, which will reveal the pathway to the syn- 

 thesis of this member of the chemical chain. 



Maltose, a sugar of the same composition as cane sugar, 

 was discovered by Dubrunfaut. Maltose, a polysaccharide, 

 has been made synthetically. 



Milk sugar, which also belongs to this same division, was 

 separated from milk as early as the year 1619, by Bartoletti, 

 of Bologna. Demole claims to have made it synthetically. 



Starches, gums, cellulose, and mucous compounds are of 

 great physiological interest in their bearing on plant life, and 

 the recent thorough investigations of the sugar groups will 

 not be unavailing to bring forward a clearer knowledge of 

 these bodies. There are many sources of starch, and some 

 peculiarities among the different kinds. Lichenin, from Ice- 



