When you are running and breathing hard, and even when you are sitting
still and breathing quietly, air is going into your lungs and then
coming out, going in and coming out, many times every minute. How does
the air get in and out of the lungs? It will not run in of itself; for
it is light and floats about, you know. Here, again, Mother Nature has
planned it all out. She has made us an air bellows, or air pump, to
suck it into the lungs. First we'll see what shape this pump is, and
then how it works.
[Illustration: THE CHEST THAT HOLDS THE LUNGS
Back of the lungs is the heart; its position is shown by the
broken line. The black line across the chest shows how high the
diaphragm rises when we breathe out quietly.]
Stiff rings of bone called _ribs_ run round your body, just like the
hoops in an old hoop skirt, or like the metal rings round a barrel.
Here is a picture of the bones of the chest. Perhaps your teacher can
show you the skeleton of some animal. You will notice how the rings,
or ribs, slant and are joined by hinges behind to the backbone and in
front to the breastbone. It looks somewhat like a cage, doesn't it?
Put your hands on the sides of your chest and you can feel your own
ribs. Do they slant upward or downward?
This chest-cage is our breathing-machine. Before I tell you how it
pumps, I want you to get a pair of bellows and see how they work. When
you lift up the handle of the bellows, you make the bag of the bellows
larger so that it sucks in air; and when you press the handle down
again, the air puffs out through the nozzle.
Our air machine, though it is somewhat different from the bellows in
shape, works in exactly the same way. You remember that you found that
the ribs slant down and can be moved on hinges. Suppose, now, you
place your hands against your ribs and feel the ribs lift as you draw
in a long breath. The air will be sucked into your nose just as it was
into the bellows when you raised the handle. By lifting your ribs, you
have made the chest-cage larger; and the air has rushed into your
nose, down your windpipe, and filled your lungs. If you breathe very
deeply, you will find that your stomach, too, swells out. This shows
that the muscular bottom of the cage, called the _diaphragm_, has been
pulled down, making the cage larger still.
In this chest-cage are millions of tiny air bags that make up the
lungs; and every time you take a breath, the air bags are puffed out
with the fresh air that comes rushing in. By the time you let your
ribs sink again, the air has given its oxygen to the blood, and the
blood has poured its carbon-dioxid smoke into the air bags for you to
breathe out. Nature, with the same bellows, pumps in the oxygen and
pumps out the "smoke."
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
water look milky. This shows that the gas in your breath is not like
the air about you; because air was all over the top of the limewater,
yet did not change it at all. The milky look is caused by carbon
dioxid, one of the poisons in your breath.
When some people come close to you, you want to turn away your head,
because you do not like the smell of their breath. Even when one is
quite well, the breath has a queer "mousey" odor, so that we never
like to breathe the breath of another person. This disagreeable odor
comes not only from the lungs but from the teeth.
We are always breathing out poisons into the air. One of these you can
see in the milky limewater, and others you can smell when you happen
to come close to anyone else.
[Illustration: PROVING THAT THE BREATH IS NOT LIKE THE AIR]
If you blow on your fingers, you feel that your breath is much warmer
than the air. If people are crowded together in rooms with doors and
windows shut, their breath soon heats and poisons the air, until they
begin to have headache, and to feel dull and drowsy and uncomfortable.
If they should be shut in too long, without any opening to let in the
fresh air, as in a prison cell, or in the hold of a ship during a
storm, the air would become so poisonous as to make them ill, and
would even suffocate them and kill them outright. Even the bees found
this out thousands of years ago; and in their hives in hot weather
they station lines of worker-bees, one just behind another from the
door right down each of the main passages, whose business it is to do
nothing but keep their wings whirring rapidly, so that they fan a
steady current of fresh air into every part of the hive.
[Illustration: DUSTING--HOW SHALL WE DO IT?]
How does Mother Nature get rid of these poisons from our breath? Of
course, you say, "She uses the wind and the sunshine." Yes, the winds
can whisk up the poison and blow it away so fast, and the sunshine can
burn up the horrid smell so quickly, that even the air above big
cities, and in their streets, is quite clean enough for us to breathe,
except where the people are very closely crowded together and very
dirty. Mother Nature wants all of us to help in keeping the air clean.
This we can do by keeping ourselves and our houses clean, and by being
careful not to leave scraps of waste, or dirty things, in the streets
and cars and parks and other public places. And you children ought to
be very careful about your school yard and the halls and the
classrooms, where you spend so much of your time.