Now, we breathe into our lung-bellows whatever air happens to be
around us. So we should take care that the air around us is fresh air.

Unless the air were kept in motion by the heat of the sun, causing
breezes and winds, it would become stale and wouldn't do at all for
our lung-bellows to use. The air we breathe must be kept moving and
fresh if it is to make us feel bright and strong and happy. Mother
Nature has given us miles upon miles and oceans upon oceans of this
clear, fresh air to breathe--"all outdoors," in fact, as far as we can
see around us and for miles above our heads. She sends the winds to
move the air about and blow away the dust and dirt; and the sunshine,
you remember, not only to warm the air and keep it moving, but to burn
right through it and kill the poisons. But this brings us to something
else.

You have learned that the air we breathe out would soon smother us,
just as smoke would; and now we will see why. If you blow against the
window pane on a cold day, the glass is no longer clear; and when you
look at it closely, you see that it is covered with tiny drops of
water. This is part of the breath you have just blown out. If the room
is cold enough, you can see your breath in the air; that is, the steam
in your breath becomes cold and appears as tiny water-drops. You have
seen how in the same way, the steam, an inch or so from the spout of
the teakettle, cools, making little water-drops that float in the air
like clouds. Part of the breath, then, is water; but most of it is a
gas, and you can't see it at all as it floats away into the air about
you.

If your teacher has a glass of limewater, and will let you breathe
into it through a tube, you will see that your breath soon makes the