the hair.

~11.~ The hair is chiefly useful as a protection. It is also an
ornament.

~12. The Nails.~--The nails of the fingers and the toes grow out of
little pockets in the skin just as the hairs do. Both the hair and the
nails are really parts of the outer skin, which is curiously changed and
hardened. The nails lie upon the surface of the true skin and grow from
the under side as well as from the little fold of skin at the root of
the nail. They are made to give firmness and protection to the ends of
the fingers and toes. The nails of the fingers are also useful in
picking up small objects and in many other ways.

~13. Uses of the Skin.~--The skin is useful in several ways:

(1) _It Removes Waste._--The sweat glands and ducts are constantly at
work removing from the blood particles which have been worn out and can
be of no further use. If we get very warm, or if we run or work very
hard, the skin becomes wet with sweat. In a little while, if we stop to
rest, the sweat is all gone. What becomes of it? You say it dries up,
which means that it has passed off into the air. Sweating is going on
all the time, but we do not sweat so much when we are quiet and are not
too warm, and so the sweat dries up as fast as it is produced, and we do
not see it. Nearly a quart of sweat escapes from the skin daily.

(2) _Breathing through the Skin._--We breathe to a slight extent through
the skin. There are some lower animals which breathe with their skins
altogether. A frog can breathe with its skin so well that it can live
for some time after its lungs have been removed. Breathing is an