II. AN EARLY ROMP

The minute you are outside the door, the fresh morning air strikes
your face, and you draw four or five big breaths, as if you would like
to fill yourself as full as you could hold. If you have had a good
night's sleep and a good breakfast, the very feel of the outdoor air
will make you want to run and jump and shout and throw your arms
about. This warms you up finely and gives you a good color; but if you
keep it up long, you will notice that two things are happening: one,
that you are breathing faster than you were before; the other, that
your heart is beating harder and faster, so that you can almost feel
it throbbing without putting your hand on your chest.

If you run too hard, or too far, you begin to be out of breath, and
your heart thumps so hard that it almost hurts. What is your heart
doing? It is pumping; it is trying to pump the blood fast out to your
muscles to give them the strength to run with.

[Illustration: AN EARLY RUN IS A GOOD PREPARATION FOR THE DAY'S
WORK]

Of course you have seen a pump? Perhaps some of you have to pump water
every day at home. You take the handle in your hands, lift it up, then
press it down, and out pours the water through the spout; and, as you
keep pumping, the water spurts out every time you press the handle
down. It is hard work, and your arms are soon tired; but, as you
cannot drink the water while it is down in the well, you must pump to
bring it up where you can reach it.

[Illustration: THE HEART-PUMP

The big tubes are the arteries and veins.]

Just so the heart pumps to keep the blood flowing round and round,
through the muscles and all over the body. If you put your finger on
your wrist, or on the side of your neck, you can feel a little throb,
or _pulse_, for every spurt from your heart-pump; and that means for
every heart-beat.

This heart-pump is made of muscle, and is about the size of your
clenched fist. And just as you can squeeze water from a sponge or out
of a bulb-syringe, by opening and shutting your hand around it, so the
big heart muscle squeezes the blood out of the heart. It squeezes it
out from one side of the heart; and then, when it lets go, the blood
comes rushing in from the other side to fill the heart again. So the
heart goes on squeezing out and sucking in the blood, all day and all
night as long as we live.

When the blood comes to the muscles, it is a beautiful bright red; but
after the musc