[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.