effect and the irritation of the cellulose needs no consideration, the
skins of the fruits may be eaten instead of being rejected. However, to
avoid any trouble, they should be well chewed.

16. Minerals in Fruit.--All fruits contain a certain percentage of
mineral salts. The quantity varies in the different kinds of fruits, but
it averages about 1 per cent. These salts have the opposite effect on
the blood from those found in meats and cereals, but they act in much
the same way as the minerals of vegetables. In other words, they have a
tendency to render the blood more alkaline and less acid. They are
therefore one of the food constituents that help to make fruit valuable
in the diet and should be retained as far as possible in its
preparation. In fact, any method that results in a loss of minerals is
not a good one to adopt in the preparation of fruits.

The minerals commonly found in fruits are iron, lime, sodium, magnesium,
potash, and phosphorus. These are in solution in the fruit juices to a
very great extent, and when the juices are extracted the minerals
remain in them.

17. Acids in Fruit.--Some fruits contain only a small amount of acid,
while others contain larger quantities. It is these acids, together with
the sugar and the volatile oils of fruits, that constitute the entire
flavor of this food. Most ripe fruits contain less acid than unripe
ones, and cooked fruits are often higher in acid than the same
fruits when raw.

Numerous kinds of acid are found in the different varieties of fruits.
For example, lemons, oranges, grapefruit, and a few other fruits
belonging to the class known as citrus fruits contain _citric acid_;