lium.=--The skin is covered with a thin layer of cells
like fine scales. These scales are called _epithelium_, or _epidermis_.
They have no blood tubes or nerves and so have no feeling. You can run a
pin under them without feeling pain. They are always growing on their
under side and wearing off on their upper side. They keep the nerves and
blood tubes of the skin from being hurt.

=125. The nails.=--The top scales of epithelium at the ends of the
fingers become matted together to make the nails. The nails keep the
ends of the fingers from being hurt. They can also be used to hold or
cut small things. The new parts of the nails form under the skin and
push down the older parts. So the nail grows farther than the end of the
finger and needs to be cut off. Biting the nails leaves their ends
rough. Then they may catch in the clothes and tear into the tender
flesh. We ought to keep the nails cut even with the ends of the fingers.

The nails are not poisonous, but the dirt under them may be. We ought
to keep them clean. Clean nails are one mark of a careful boy or girl.

=126. Hair.=--Some of the scales of epithelium over some parts of the
body dip into tiny holes in the skin. In each hole they become matted
together to form a _hair_. Fine short hair grows on almost every part
of the body. On the top of the head it grows long and thick. When
boys become men, it also grows long upon their faces. The skin pours
out a kind of oil to keep the hair soft and glossy.

[Illustration: =A hair (x200).=

_a_ the surface of the skin.
_b_ a hair.
_c_ an oil gland.
_d_ a muscle to make the hair stand on end.
_e_ and _g_, the growing cells of the hair.
_f_ fat in the skin.]

=127. Care of the hair.=--The hair may become dirty like any other
part of the body. Brushing it takes out a great deal of dirt, but you
should also wash it once a week.

The oil in the skin ought to be enough for the hair. Hair oils do not
do the hair any good. If you wet the hair too often, you may make it
stiff and take away its gloss. It is best to comb the hair dry. Brush
it so as to spread the oil of the skin. Hair dyes are poisonous, and
ought not to be used.

=128. The sweat or perspiration.=--The scales of epithelium dip into
the skin and there line tiny tubes. The tubes form the _sweat_, or
_perspiration_, out of the blood. The tubes are too fine to be seen,
but they are upon almost every part of the body. They take the ashes
or other