ts specific rotatory power of
+22 deg.). When dissolved in alcohol, this change does not take place
because of the absence of the excess of water necessary to produce the
intermediate aldehydrol form.

There are other examples of the existence of the [alpha] and [beta]
modification of glucose. For example, [alpha]-methyl-glucoside and
[beta]-methyl-glucoside (specific rotatory powers, +157 deg. and -33 deg.,
respectively) are both known, as well as several other similar glucoside
arrangements.

=Mannose.=--This sugar does not occur as such in plants; but complex
compounds which yield _d_-mannose when hydrolyzed, known as "mannosans,"
are found in a number of tropical plant forms. The mannose which is
obtained from these by hydrolysis is very similar to glucose in its
properties, forms the same osazones as do glucose and fructose, exhibits
mutarotation, etc. Mannose may also be obtained by oxidizing mannitol, a
hexatomic alcohol, known as "mannite," which occurs in many plants,
especially in the manna-ash (_Fraxinus ornus_), the dried sap from which is
known as "manna."

=Galactose= occurs in the animal kingdom as one of the constituents of
lactose, or milk-sugar. It is also one of the constituents of raffinose, a
trisaccharide sugar found in plants, and occurs as "galactans" in many gums
and sea-weeds. The _d_-galactose, obtained by the hydrolysis of any of
these compounds, is a faintly sweet substance which resembles glucose in
many of its properties; having one characteristic difference, however, in
that it forms mucic acid instead of saccharic acid when oxidized by
concentrated nitric acid. These oxidation products are very different in
their physical properties and this difference serves to distinguish between
the two sugars from which they are derived.

=Fructose= (levulose, honey sugar, or "diabetic" sugar) occurs along with
glucose in the juices of many fruits, etc. It is a constituent of sucrose,
of raffinose, and of the polysaccharide inulin, from which it may be
obtained by hydrolysis. It is a ketose sugar, reduces Fehling's solution,
forms the same osazone as glucose, and is easily fermentable by yeast. Its
sweetness is slightly greater than that of ordinary cane sugar.
_d_-fructose (the ordinary form) is easily soluble in water, and is
strongly levorotatory, its specific rotatory power at 20 deg. C. being
-92.5 deg.; it is unique in the very large effect which is produced in
its rotatory power by incre