a marble or a pencil in the hand you know what it is by the feeling of
the object. This kind of feeling is called the sense of touch.

~13.~ There are other nerves of feeling by means of which we are able to
hear, see, taste, and smell, of which we shall learn in another lesson.
Besides these we have nerves which tell us whether objects are cold or
hot, and heavy or light. Nerves of feeling also tell us when we are
hungry, or thirsty, or tired, and when we need more air to breathe.

~14. Nerves of Work.~--There are other nerves which are made just like
the nerves of feeling, but which do not feel. These nerves have a very
different use. They come from cells in the brain which have charge of
the different kinds of work done in the body, and they send their
branches to the parts which do the work; hence we call them _nerves of
work_.

~15.~ One set of cells sends nerves to the heart, and these make it go
fast or slow as is necessary. Another sends nerves to the liver,
stomach, and other digestive organs, and causes them to do their part in
the digestion of the food. Other cells send branches to the muscles and
make them act when we wish them to do so. Thus you see how very useful
the brain and nerves are. They keep all the different parts of the body
working together in harmony, just like a well-trained army, or a great
number of workmen building a block of houses. Without the brain and
nerves the body would be just like an army without a commander, or a lot
of workmen without an overseer.

~16. How we Use the Nerves.~--If you happen to touch your hand to a hot
stove, what takes place? You will say that your arm pulls the hand away.
Do you know why? Let us see. The nerves of feeling in the hand tell the