Sugar has a chemical composition very nearly resembling starch, but it
differs in both chemical and physical properties. Sugar is soluble in
water, whilst starch is only diffusible through it. Sugar undergoes the
process of fermentation, which starch does not. Sugar has a sweet taste,
while starch is almost tasteless. Starch is, however, convertible into
sugar by the agency of nitrogenous substances. If starch is placed in
contact with saliva a little time it becomes soluble, and gives the
reactions of sugar; and it is probable that in this way starch itself
becomes absorbed into the blood. Sugar, like starch, assumes various
forms, and three of these are found in common articles of diet. These
are cane sugar, grape sugar, and milk sugar.
The action of sugar on the system is identical with starch. As it is
more readily absorbed into the blood than starch, it is better adapted as
a force-producer for the young. Hence it is found supplied to the young
in all the mammalia, in the milk secreted by their mothers. That it is
adapted for the young is shown by the instinctive propensity children
display to partake of this form of diet. Although adapted for children,
the facility with which it decomposes renders it frequently injurious to
adults.
Most plants contain sugar in their roots. But in some large quantities
are deposited, as in the sugar beet, which is employed most extensively
in France and on the continent of Europe for the supply of sugar for
dietetical purposes. A series of specimens illustrating products from
beet-root, including sugar, from Messieurs Serret, Hamoir, and Co., of
Valenciennes, are exhibited in the Collection.
Sugar is the basis of all kinds of confectionery, specimens of which are
exhibited by Messrs. Fortnum and Mason, of Piccadilly, in Case 111.
Samples of sugar are exhibited in Cases 17, 110, 112, and 113, some of
which have obtained been from other plants than the sugar cane.
Fruits after being saturated with sugar are also preserved and kept dry.
In Case 15 preserved fruits of various kinds are exhibited by Messrs.
Fortnum and Mason. It is in this way that fruits are brought to this
country which otherwise would not be seen on account of their perishing
nature.
_Treacle_ or _Molasses_ is the uncrystallized portion of sugar which is
separated by draining from the brown sugar.
_Grape Sugar_ or _Glucose_ is found in the fruits of plants, and is
especially abundant in the grape. Grapes, when dried, are eaten on
account of the glucose they contain. They are known in the shops under
the name of “plums,” “raisins,” and “currants.” The latter word is a
corruption of Corinth, the small grape yielding this, being cultivated in
the vicinity of Corinth, on the classic soil of Greece.
Dried fruits of the grape-vine, presented by Messrs. Fortnum and Mason,
Piccadilly, are exhibited in Case 14.
_Honey_, which is the stored food of the bee, contains both
crystallizable and uncrystallizable grape sugar. The crystals of the
former may be easily detected by the aid of a low power of the
microscope. Samples of British honey, and honey from France, Russia, and
other countries, may be seen in Cases 18.
_Substances resembling Sugar_, such as dextrin, gum, liquorice, manna,
&c., are exhibited in Case 107. Among plants yielding sugar may be noted
the Chinese sugar millet (Case 17), sweet potato (Case 8), turnips (Case
11), carrots (Case 11), and Jerusalem artichoke (Case 12), the analyses
of which are exhibited.