200 THE CARBOHYDRATES. 



noses have shown that in rabbits the Z-arabinose and the d-mannose are 

 much better utilized than d- and r-arabinose or I- and r-mannose. These 

 observations as well as the varying fermentability of the sugars are only 

 a few examples showing the great influence that chemical structure, and 

 configuration have upon chemical compounds in making the material 

 changes in the animal and plant kingdom. 



In the alcoholic fermentation the sugar is decomposed according 

 to the general equation C 6 Hi 2 O 6 =2C 2 H 6 O + 2CO2. The exact process 

 is not clear, and seems to be rather complicated. According to the inves- 

 tigations of BUCHNER and MEISSENHEIMER, STOKALSA and MAZE, 1 we are 

 dealing here with the complex action of two enzymes, of which one, 

 the zymase (BUCHNER and MEISSENHEIMER), transforms the sugar 

 into lactic acid, while the other, the lactacidase (BUCHNER and MEISSEN- 

 HEIMER) splits the lactic acid into alcohol and carbon dioxide. Accord- 

 ing to certain investigators methyl glyoxal, CHyCO.COH, is formed 

 intermediary between the sugar and the lactic acid. 2 



As previously mentioned, the sugars also undergo other fermentations, 

 namely lactic acid and butyric acid fermentation. 



The monosaccharides are colorless and odorless bodies, neutral in 

 reaction, with a sweet taste, readily soluble in water, generally soluble 

 with difficulty in absolute alcohol, and insoluble in ether. Some of them 

 crystallize well in the pure state. They are strong reducing substances. 

 They reduce metallic silver from ammoniacal silver solutions and they 

 also reduce other metallic oxides such as copper, bismuth and mercury 

 oxides, on heating in alkaline solution. This behavior is of great 

 importance in the detection and quantitative estimation of the 

 sugars. 



The simple varieties of sugar occur in part in nature as such, already 

 formed, which is the case with both of the very important sugars, dex- 

 trose and levulose. They also occur in great abundance in nature as 

 more complex carbohydrates (di- and polysaccharides) ; also as ester- 

 like combinations with different substances, as so-called glucosides. 



Among the groups of monosaccharides known at the present time, 

 those containing less than five and more than six carbon atoms in the 

 molecule have no great importance in biochemistry, although they are 

 of high scientific interest. Of the two groups the hexoses are the more 

 abundant and are of special interest. The pentoses are becoming of 



1 Buchner and Meissenheimer, Ber. d. d. chem. Gesellsch., 37 and 38; Stoklasa, 

 Ber. d. d. Botan. Gesellsch., 22, pages 358 and 460; Maze", Compt. rend., 138. 



2 Buchner and Meissenheimer, 1. c. and Ber. d. d. chem. Gesellsch., 39. In regard 

 to the chemical processes in alcoholic fermentation see also Schade, Zeitschr. f. 

 physikal. Chem., 57, and Biochem. Zeitschr., 7; Wohl, ibid., 5; Slator, Ber. d. d. chem. 

 Gesellsch., 40. 



