"body fires" and keeps you warm, and at the same time makes you grow.
Of course the "body fires" are not just like those you see burning in
the stove: there are no flames. But there is burning going on, just
the same.

The food you put into your body must be made soft and pulpy before it
can burn in your muscles. Now you can guess what your teeth are for.
They chop, crush, and grind the food; and the tongue rolls it over and
over and mixes it with the moisture in your mouth, until it is almost
like very thick soup. Then you make a little motion with your tongue
and throat, and down it goes.

[Illustration: THE FOOD TUBE

Note the arrows. This is the trip made by every mouthful of
food.]

Where does it go? It is passed down a tube that we call the _food
tube_. While I tell you about it, you can look at the picture and then
try to draw it yourself.

The food goes quickly down the first part of the tube until it comes
to a part much larger than the rest, which we call the _stomach_. Here
it is churned about for a long time, and the meat you have eaten is
melted, or dissolved. Then the food goes on into the next part of the
tube, which has become narrow again. This lower part, which is about
twenty-five feet long, is coiled up just below the waist, between the
large bones that you can feel on each side of your body. These coils
of the food tube, we call the _bowels_.