Sunlight can increase the amount of pigment in the skin. The people
who live in the torrid zone have much darker skins than those who live
where the days are short and cold. You have noticed, yourself, that
when you expose the skin of your face or arms to the hot sun, you
become freckled, or tanned. This tanning, or browning, of the outer
layer of the skin protects the more delicate coats of skin below from
being scorched or injured by the strong light.

When you are playing and running with your schoolmates, you see that
their faces grow very red, and even their hands. Why is this? Because
the heart has been pumping hard and has sent the red blood out toward
the skin. The red color shines through the outer part of the skin. The
pigment in the Indian's skin, or the negro's, prevents the red blood
underneath from shining through, as it does through yours.

[Illustration: THE PARTS OF THE SKIN

The pore P on the surface of the skin is the end of a tube
through which sweat flows out. At O are the oil sacs that feed
the hair H. At B are the little blood vessels that make the skin
look pink.]

The skin, you see, is made up of different layers. When you burn
yourself, you can see a layer of skin stand out like a blister. It is
white; but if the blister is broken, underneath you see the coat that
is full of tiny blood vessels, so tiny and so close together that this
whole coat looks red. The skin, like every other part of the body, is
made up of tiny animal cells. In the outer coat they become quite flat
like little scales and then wear off; and their places are taken by
the newer cells that are growing from beneath. The skin grows from