6 CHEMICAL CONSTITUENTS OF BOD Y AND FOOD. 



obtained by reduction through the intermediate osone (see p. 9). The sugar 

 obtained is identical with levulose or fructose, except that it is optically inactive. 

 If this inactive levulose (i-levulose) is submitted to the action of yeast, the 

 levorotatory constituent (cMevulose) ferments, and the residue is dextro- 

 rotatory. This is Z-levulose, 1 but it is not the natural sugar. The natural 

 sugar was formed in the following way : a-acrose was reduced to the corre- 

 sponding alcohol, a-acrite, which is identical with i-mannite ; from this the 

 sugar 2-mannose was obtained, which was fermented, and Z-mannose alone 

 remained. By further oxidation i-mannose yields ^-mannonic acid. By 

 fractional crystallisation of the morphine or strychnine salt of this acid, it can 

 be separated into its two active (d and Z) constituents, and from these the 

 corresponding sugars (mannoses) are obtained by reduction, and these by 

 means of the ozones into the corresponding levuloses, the fZ-levulose being 

 the levorotatory natural sugar. 



In order to get dextrose, the d- and 7-mannonic acids are heated with 

 quinoline ; this partly decomposes these acids, yielding d- and /-gluconic acids, 

 and by reduction of these acids the sugars cZ-glucose (or dextrose) and /-glucose 

 are obtained. 



Of the numerous sugars in the monosaccharide group, dextrose, 

 levulose, and galactose possess special physiological interest. 



Dextrose is found widely distributed in nature in grapes, and many 

 other fruits ; also in seeds and roots, and in honey. It is generally 

 mixed with levulose. In the animal body it is the final result of the 

 digestion of starch, and occurs in small quantities in the blood and 

 lymph ; traces only occur in normal urine. The quantity both in the 

 blood and urine is increased in diabetes. It crystallises either in fine 

 needles, free from water of crystallisation, or with 1 molecule of water of 

 crystallisation in small plates ; these melt at 100 and lose their water 

 at 110 C. The water-free crystals melt at 146 and at 170 C. lose 

 water, the residue being glucosane (C 6 H 10 5 ). By higher temperatures 

 it is converted into caramel. 



Dextrose is readily soluble in water ; the solution is not so sweet as 

 one of cane-sugar; it is dextrorotatory. The specific rotation 2 varies 

 with temperature and concentration, but at 20 C. averages + 52 0- 6. 

 A freshly -made solution may have nearly double this rotatory power, 

 but on standing for some time, or on heating the solution, the rotation 

 becomes normal. Dextrose is slightly soluble in cold, very soluble in 

 hot alcohol. It is insoluble in ether. 



Levulose is found with dextrose in the vegetable kingdom, and in 

 honey. It is formed by the hydrolytic splitting of cane-sugar and other 

 carbohydrates, but is obtainable with special ease from inulin. It is 

 occasionally found in diabetic urine. 3 In many cases of diabetes it may 

 be used with impunity in the food. 



1 The I, i, and d are prefixes primarily attached to isomeric sugars, to indicate their action 

 on polarised light, which is due to the presence and position of an asymmetric carbon atom. 

 The terms were introduced by Fischer to denote this character, but they have been extended 

 to comprise derivatives of the original sugar, which derivatives may have the opposite 

 rotatory power, as is seen in the above example, where a d sugar is levo- and an I sugar is 

 dextrorotatory. 



2 The specific rotation (a) D of any substance is the amount of rotation in degrees of a 

 circle of the plane of polarised light, produced by 1 grm. of the substance dissolved in 

 1 c.c. of liquid, examined in a tube 1 decimetre long. It is measured for yellow (sodium) 

 light. 



3 Leo (Virchoio's Archiv, 1887, Bd. cvii. S. 108) has found as an occasional constituent 

 of diabetic urine, a levorotatory sugar which is not levulose. Its reducing power is small, 



