le the
blood is filling it again. So it really rests one half of the time.

=85. Arteries.=--The heart pumps the blood through a single tube. This
tube opens into smaller tubes. These open into still smaller ones. You
must use a strong microscope to see the finest blood tubes. The tubes
reach every part of the body, and carry blood to its cells. They are
called _arteries_. At each heart-beat a wave of blood can be felt in
an artery. This wave is the _pulse_. It can be felt in the wrist,
temples, and other places. By the pulse we can tell how often and how
strongly the heart is beating.

[Illustration: =Arrangement of capillaries.=

_a_ smallest artery.
_b_ smallest vein.
_c_ network of capillaries.]

=86. Capillaries.=--The smallest arteries divide into a fine network
of small tubes. These tubes are the _capillaries_. They lie around
every cell of the body. Their sides are very thin. As the blood flows
through them, some of it soaks through the sides of the tubes. Blood
contains all kinds of food for the cells. Each cell is always wet with
food and can eat it at any time. The cells are like the tiny animal,
the ameba, and can take in the food by any part of their bodies. The
cells are better off than the ameba, for their food is brought to
them. They pay the body for their food by working for it.

=87. Veins.=--The capillaries come together again to form large tubes.
These tubes are called _veins_. Only a little of the blood goes through
the sides of a capillary. The rest flows on into the veins. The veins
unite to form two large tubes. These two tubes open into the heart.

=88. How the blood flows.=--The blood is pumped out of the heart,
through the arteries to the capillaries. There some goes out to the
cells. The rest flows into the veins and goes back to the heart. All
the blood in the body passes through the heart every two minutes. It
takes only twenty seconds for a drop of blood to go from the heart to
the toes and back again. The arteries are deep in the flesh, but some
of the large veins can be seen upon the back of the hands.

=89. Bleeding.=--If a large artery or vein is cut there is a great
deal of bleeding. You can always stop a cut from bleeding by holding
it fast between the hands. Do not be afraid of the blood when you see
any one bleeding, but hold the sides of the cut tightly with both of
your hands. This will stop any bleeding until help comes. You may keep
a person from bleeding to dea