he juice
itself. The latter is water, with a small proportion of fruit sugar
(from one to twenty per cent in different varieties), and vegetable
acids. These acids are either free, or combined with potash and lime in
the form of acid salts. They are mallic, citric, tartaric, and pectic
acids. The last-named is the jelly-producing principle.

While the juice, as we commonly find it, is readily transformable for
use in the system, the cellular structure of the fruit is not so easily
digested. In some fruits, as the strawberry, grape, and banana, the cell
walls are so delicate as to be easily broken up; but in watermelons,
apples, and oranges, the cells are coarser, and form a larger bulk of
the fruit, hence are less easily digested. As a rule, other points being
equal, the fruits which yield the richest and largest quantity of
juices, and also possess a cellular framework the least perceptible on
mastication, are the most readily digested. A certain amount of waste
matter is an advantage, to give bulk to our food; but persons with weak
stomachs, who cannot eat certain kinds of fruit, are often able to
digest the juice when taken alone.

Unripe fruits differ from ripe fruits in that they contain, starch,
which during ripening is changed into sugar, and generally some
proportion of tannic acid, which gives them their astringency. The
characteristic constituent of unripe fruit, however, is pectose, an
element insoluble in water, but which, as maturation proceeds, is
transformed into pectic and pectosic acids. These are soluble in boiling
water, and upon cooling, yield gelatinous solutions. Their presence
makes it possible to convert the juice of ripe fruits into jelly. Raw
starch in any form is indigestible, hence unripe fruit should never be
eaten uncooked. As fruit matures, the changes it undergoes are such as
best fit for consumption and digestion. The following table shows the
composition of the fruits in common use:--

ANALYSIS.

Water. Albumen. Sugar. Free Acid. Pectose. Cellulose Mineral
Matter.
Apples 83.0 0.4 6.8 1.0 5.2 3.2 0.4
Pears 84.0 0.3 7.0 0.1 4.6 3.7 0.3
Peaches 85.0 0.5 1.8 0.7 8.0 3.4 0.6
Grapes 80.0 0.7 Glucose. Tartaric. 3.1 2.0 0.4