100 THE CHEMICAL COMPOSITION OF THE BODY 



alkaline solution. It undergoes alcoholic fermentation with yeast and acid 

 fermentation with certain bacteria. 



CH 2 OH CH 2 OH 



I I 



CHOH CHOH 



I I 



CHOH CHOH 



I ! 



CHOH CHOH 



I I 



CHOH CO 



! 



CHO CH 2 OH 



Dextrose. Levulose. 



Levulose (fructose) is a ketose and is found associated with dextrose 

 in many fruits, the mixture probably being produced by the hydrolysis of, or 

 preceding the synthesis of, cane-sugar. It may be prepared by the hydrolysis 

 of inulin and, along with dextrose, by the inversion of cane-sugar on boiling 

 with dilute mineral acids or through the action of specific enzymes. It is 

 levorotatory, [a] d = 92. Levulose may be crystallized with difficulty in 

 needles. It has a sweet taste. It reduces alkaline solutions of the 

 metallic oxides, but not so much as dextrose, and yields an osazone identical 

 with glucosazone. It undergoes fermentation, but less readily than dextrose. 



Galactose is obtained with dextrose from milk-sugar or lactose on 

 boiling with dilute mineral acids. It is less soluble in water than levulose 

 or glucose. It reduces metallic oxide in alkaline solution, forms a charac- 

 teristic osazone which melts at 193-4 C. and it undergoes slow fermentation 

 by yeast. It is dextrorotatory. 



It is also obtained on hydrolysis of cerebrin, a glucoside occurring in 

 nervous tissue. 



Maltose (malt-sugar) is produced by the action of amylolytic enzymes 

 on starch and glycogen. It crystallizes in small needles, is strongly dextro- 

 rotatory, [a] d = +140.6, reduces alkaline copper solutions much feebler 

 than dextrose, and does not reduce bismuth oxide. It forms a characteris- 

 tically crystalline osazone, melting at 206 C. It is readily soluble in water 

 and only slightly soluble in alcohol. Maltose is not so sweet as cane-sugar. 

 It does not undergo alcoholic fermentation with yeast unless first split into 

 dextrose. On boiling with dilute mineral acids or through the action of 

 inverting enzymes, it is hydrolyzed into dextrose. 



Saccharose (cane-sugar) is obtained from many plants, such as the 

 sugar beet and sugar cane, and from the sap of certain trees, as the sugar 

 maple. It crystallizes in prisms, is soluble in water, and only very slightly 

 soluble in alcohol. Cane-sugar is not directly fermentable by yeast. It is 

 levorotatory. Saccharose has no reducing action on alkaline copper solution 



