all the structures in the body.

Often we think of the body as a beautiful house. Now a house does not
look very beautiful when it has dust and crumbs on the floor, buckets
of greasy dishwater in the kitchen, and smoke from the furnace in the
air! You could not live in such a place. No, the smoke must go out up
the chimney, the dust and crumbs must be swept away, the dirty water
must be drained off in pipes; the house must be not only cleaned, but
kept clean all the time. This is true of your body, too.

Now Mother Nature sends the smoke from the body out through the lungs,
and the crumbs and solid dirt down and out by means of the food tube.
But the waste water--how does she get rid of that? The waste water,
you remember, is in the blood vessels, mixed with the blood. How does
she get it out of the blood? She sends it through three magic
cleaners, or strainers,--the _skin_, the _liver_, the _kidneys_.

That the skin is a strainer, you already know; for you know how the
skin lets out the waste water in perspiration, or sweat, and how
important it is that we keep the little holes of the strainer open and
clean. And you know, too, that most of the water that passes out of
the body goes first to the kidneys.

The liver, however, is the largest cleaning machine of all and has to
work very hard. The blood comes to it full of foods and poisons. This
wonderful cleaner picks out the food it needs and takes up many of the
poisons, too. "What does it do with the poisons?" you ask. Some of
them it changes into good food, and others it makes harmless and sends
away down the food tube in a fluid called _bile_. If we are strong and
healthy, the liver has the power to kill many of the disease germs