lm of the hand you will see
many coarse lines, and by looking much closer you will see that the palm
is completely covered with very fine ridges and furrows. Now, if you
examine these ridges with a magnifying-glass, you will find arranged
along each ridge a number of little dark spots. Each of these points is
the mouth of a very small tube. This is called a _sweat duct_. These
ducts run down through both the outer and inner layers of the skin. At
the under side of the true skin the end of the tube is rolled up in a
coil, as you can see by looking at the illustration on the following
page. The coiled parts of the tubes are called _sweat glands_, because
they separate from the blood the fluid which we call sweat or
perspiration.

~8. The Oil Glands.~--There are other little glands in the skin which
make fat or oil. The oil is poured out upon the skin to keep it soft and
smooth.

[Illustration: THE STRUCTURE OF THE SKIN.]

~9. The Hair.~--There are some curious little pockets in the skin. Out
of each of these pockets grows a hair. On some parts of the body the
hairs are coarse and long; on other parts they are fine and short.

~10.~ Many of the ducts leading from the oil glands open into the
pockets or pouches from which the hairs grow. The oil makes the hair
soft and glossy. Nature has thus provided an excellent means for oiling
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 g