6 CHEMICAL CONSTITUENTS OE BODY AND EOOD. 
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 (/-levulose) is submitted to the action of yeast, the 
levorotatory constituent ('/-levulose) 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 /-mannite ; from this the 
sugar /-mannose was obtained, which was fermented, and /-mannose alone 
remained. By further oxidation /-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 /) constituents, and from these the 
corresponding sugars (mannoses) are obtained by reduction, and these by 
means of the ozones into the corresponding levuloses, the rf-levulose being 
the levorotatory natural sugar. 
In order to get dextrose, the d- and /-mannonic acids are heated with 
quinoline ; this partly decomposes these acids, yielding d- and /-gluconic acids, 
and by reduction of these acids the sugars '/-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 O 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 hydrolvtic 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, hut they have been extended 
to comprise derivatives of the original sugar, which derivatives may have the opposite 
rotatory power, as is seen in the ahove example, where a d sugar is levo- and an I sugar is 
dextrorotatory. 
- The specific rotation («)o of any substance is the amount of rotation in degrees of a 
circle of the plane of polarised light, produced by 1 grni. 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 {Virchmo's Arehiv, 1SS7, Bd. cvii. S. 108) has found as an occasional constituent 
of diabetic urine, a levorotatory sugar winch is not levulose. Its reducing power is small, 
