[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 of the kidneys; for, like the liver, they are
sometimes over-worked and do not carry the poisons from the body. You
are helping your kidneys when you drink plenty of fresh clean water
every day, and also when you play or work hard enough to get into a
good perspiration; for, as perspiring carries out some of the poisons,
it leaves less for the kidneys to pour out. You ought to get into a
good perspiration at least once every day, or better, three or four
times, if you wish to keep healthy. The Bible says, "In the sweat of
thy brow shalt thou eat bread"; and you must earn health and happiness
at the same price.


II. SOME FOES TO FIGHT

You have seen that sitting or sleeping in rooms where the air is bad,