METABOLISM OF CARBO-HYDRATES GLYCOGEN 537 



oxidation, is glycerose (C 3 H 6 O 3 ), a substance with the typical 

 properties of a sugar. In the laboratory it has been shown that 

 two molecules of glycerose can be combined to form one molecule of 

 sugar of the hexose type with six carbon atoms (C 6 H 12 O 6 ) . A similar 

 transformation is accomplished in the liver, and then a number of 

 the monosaccharide molecules (C 6 H 12 O 6 ) are condensed with loss of 

 water to form glycogen. Thus, w(C 6 H 12 O 6 ) H 2 O = (C 6 H 10 O 5 )w. 

 Since glycerin is a normal product of the hydrolysis of fats, the 

 possibility that the fats of the food may contribute through their 

 glycerin component to glycogen formation must be admitted. The 

 monosaccharides dextrose, levulose, and galactose gave a similar 

 result, while the disaccharides cane-sugar and lactose caused no 

 increase in the glycogen of the perfused liver, since the liver contains 

 no ferment capable of splitting them into monosaccharides. And 

 although the first step in the linking of the monosaccharide mole- 

 cules would seem to be the formation of a disaccharide such as 

 maltose, the glycogen molecule must apparently be built up from 

 single ' bricks,' the monosaccharides, and cannot be constructed 

 from bricks which are already coupled in pairs, the disaccharides. 

 Of course, since the disaccharides are hydrolysed in the digestive 

 tube to simple sugars, they are to be reckoned with the true glycogen- 

 formers, for in the intact body they are presented to the hepatic 

 cells in the form of monosaccharides. It is probable that levulose 

 and galactose are first changed into dextrose. 



By the action of alkalies such structurally related sugars can easily 

 be transformed into each other. Thus dextrose is an aldehyde of an 

 alcohol with six carbon atoms, and levulose the corresponding keto- 

 hexose. 



By oxidizing the alcohol we get an aldehyde or a ketone, according 

 to whether a primary alcohol group (CH a .OH) or a secondary group 

 (CH.OH) is oxidized, with the loss of two atoms of hydrogen. The 



aldehyde is characterized by the presence of the group \v> the 



ketone by the group CO. Both the aldehyde and the ketone are 

 sugars, and since each contains six carbon atoms, they are both sugars 

 of the group known as ' hexoses.' Dextrose, being not only a hexose 

 but an aldehyde, may be called an ' aldohexose,' and levulose, being 

 not only a hexose but a ketone, a ' ketohexose.' 



CH a .OH C/2 CH a .OH 



I l x I 



CH.OH CH.OH CO 



CH.( 



CH.OH CH.OH CH.OH 



CH.OH CH.OH CH.OH 



CH.OH CH.OH CH.OH 



CH a .OH CH 2 .OH CH 2 .OH 



6-valent alcohol. Aldehyde. Ketone, 



