shaped
centre, a kind of deck, and in this centre they carry the freight. They
take on this freight at the Lung Station. They have something on deck
which holds on to the goods they get at the station, to keep it from
being lost on its long journey.

It never overflows its banks. Its color is not bright and blue as the
waters of the Hudson or Potomac Rivers. It is yellow and red, like the
Mississippi, the great "Father of Waters." If you would taste it you
would find it to be salty like the ocean.

As soon as the little boats load up at the Lung Station, off they sail
on this wonderful stream, carrying their freight to the Muscle Country,
the Skin Country or the Gland Country. When the boats reach one of these
countries, they unload and the little men of these countries (or cells)
take the freight and put it just where it is needed. The freight is
called oxygen. The Lung Station is filled with it every time a person
takes a good breath of pure fresh air.

The little boats come to Lung Station and load up with oxygen about
three times every minute, so you see how fast they travel. This freight
is the thing that paints our cheeks a rosy color and gives us good
health.

When each little boat has unloaded its cargo in the far countries, the
little cell men load them with a return cargo, which is made up of waste
matter (carbon dioxide). This cargo is carried back to the Lung Station,
and unloaded there. It is breathed out into the air, through the air
tubes.

[Illustration]

If we breathe impure air, the little boats go back to the far countries
with only a small cargo of oxygen. Then the cell men feel as if they are
cheated and refuse to do good work for us. In fact, they grow weak and
cannot do as good work as they could if the boats brought a full cargo
of fresh air.

There is another boat in the stream; just look at its queer shape, and,
queerer still, this little boat is changing its shape. Is not that
funny? Now the small end is toward us, now the large end, and now it is
round like the little freight boats, only it is larger.

I wonder what kind of a vessel it is. It is larger than the freight
boat. There are not so many of these boats either, not half so many as
there are freight boats. They are flying white flags, and belong to the
White Squadron. I wonder if that means peace.

No, they are war-vessels. Let us see what these white ships are doing.
We will call them Dreadnoughts. Watch them as they move