THE DI8ACOBARIDBS. 57 



positions which are thus effected may be represented by the equa- 

 tions : 



(1) C 6 H u O e = 2C 2 H 5 (OH) + C0 2 . 



Ethyl alcohol. 



(2) C 6 H 12 O 6 = 2CH 3 CIT.OH-COOH. 



Lactic acid. 



(3) 2C 3 H 6 3 = C 3 H 7 .COOH + 2CO 2 + 4H. 

 Lactic acid. Butyric acid. 



Of the hexoses, glucose only is found in the animal body ; while 

 laevulose, mannose, and galactose do not occur as such, and on reach- 

 ing the liver are apparently immediately transformed, together with 

 glucose, into the poly saccha ride glycogen. Whether or not a trans- 

 formation into glucose first takes place, and whether this can occur 

 in the intestinal mucosa, is unknown. The amount of glucose which 

 may be found in the blood and lymph, and in the various tissues of 

 the body, is always small. 



Lsevulose occurs in nature together with glucose, most abundantly 

 in various fruits, the roots and seeds of many vegetables, and also in 

 honey. It further results during the hydrolytic decomposition of 

 cane-sugar, inulin, and other carbohydrates. It is readily soluble in 

 water, and its aqueous solutions, in contradistinction to common 

 glucose, are Isevorotatory. It may be obtained in crystalline form, 

 but with difficulty. It is fermentable, and gives the same reduc- 

 tion-tests as glucose (which see). With phenylhydrazin laBvulose 

 yields the same osazon. 



Galactose is formed during the hydrolytic decomposition of 

 lactose and many other carbohydrates. It is also obtained from 

 cerebrin on heating with dilute mineral acids. It is not so readily 

 soluble in water as glucose, but like it is dextrorotatory. Galactose 

 crystallizes in needles and platelets which melt at 168 C. It is 

 fermentable, and yields an osazon which melts at 193 C. It re- 

 duces an alkaline solution of cupric oxide, but to a less marked 

 degree than glucose. On oxidation it yields first galactonic acid and 

 later mucinic acid. 



Glucose will be considered in a subsequent chapter, where the 

 methods of testing for the simple sugars in general, and also their 

 quantitative estimation, will be described. 



THE DISACCHARIDES. 



The disaccharides result from the monosaccharides through a con- 

 densation of the anhydrides of two monosaccharine molecules, analo- 

 gous to the formation of ethers from alcohols. On hydrolytic de- 

 composition they accordingly yield two monosaccharine molecules, 

 which represent either one and the same substance or two isomeric 

 bodies. Some of the disaccharides occur in nature as such, while 

 others result from the decomposition of still more complex carbo- 

 hvd rates. 



