e of sawdust
dropping, dropping, dropping, one after the other, from a hole in the
log. I looked into the hole, and what do you think I saw? Hundreds of
little brown ants, busy as could be carrying the sawdust, throwing it
out, and then scurrying back to get some more. Several feet inside the
log, other ants were cutting the sawdust, hollowing out the rooms of
their house; and in another part others were getting food for the
workers, and still others taking care of the baby ants. They were all
helping one another, and whatever one ant did helped all the rest.
That is the way with the parts, or organs, of the body. When one part
works well, it helps all the rest; when one squad of tiny cells in the
muscles or liver or heart is doing its duty, like the little ants, it
helps all the other cell-workers in the body to keep healthy.

If you eat proper food, you help not only your stomach but your liver,
too; for it has not so many poisons to get rid of. While you are
helping your stomach and your liver, you are helping your heart and
your brain, and so on. So what you do to help one helps all.

There are, however, some poisons that the liver cannot get rid of; but
these the skin or the kidneys carry away. Have you ever seen kidney
beans? The bean is the shape of a kidney. The kidneys are in the
middle of your back, packed close to your backbone, on a line with
your waist. This is a picture of them. Do you see the little tubes
leading down from the kidneys, carrying the waste water and poison
down into a kind of bag? The walls of this bag, called the _bladder_,
will stretch, and it will hold about a pint of waste water. From the
bladder a tube carries the water down out of the body.

[Illustration: THE KIDNEYS AND THE BLADDER

The large tubes are the artery and the vein that carry blood to
and from this part of the body.]

You can help your kidney-strainers by emptying your bladder at certain
times each day. Some children have to empty the bladder much oftener
than others, but most children can form what we call _regular habits_
about it, by trying to do it at the same times each day. If you are
quite strong, five times a day is often enough: when you first get up,
at recess, at noon, at four o'clock, and at bedtime. Many children do
it much oftener than this; but as they grow older and the muscles grow
stronger, they slowly outgrow this trouble, if they try to form the
right habits.

There are many diseases