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 nerve cells in the brain from which they come that the hand is being burned.

The cells which feel cannot do anything for the hand, but some of their branches run over to another part of the brain, which sends nerves down to the muscles of the arm.

These cells, through their nerve branches, cause the muscles to contract.

The cells of feeling ask the cells which have charge of the muscles to make the muscles of the arm pull the hand away, which they do very quickly.
~17.~ So you see the nerves are very much like telegraph or telephone wires.