Then we can drill a hole in the skull directly over it and remove the tumor, lift up the splinter of bone, or tie the ruptured blood vessel.
Three other patches, or areas, running along the side of the brain, each of them about two inches across, are known to be the centres for smell, hearing, and sight, that for sight lying furthest back.

Damage to one of these areas will make the individual more or less completely blind, or deaf, or deprived of the sense of smell, as the case may be.
At the lower part of the area which controls the muscles of the different parts of the body, above and a little in front of the tip of the ear, lies a very important centre, which controls the movements of the tongue and lips, and is known as the _speech centre_.

If this should be injured or destroyed, the power of speech is entirely lost.

This, curiously enough, lies upon the left side of the brain, and is the only one-sided centre in the body.

Why this is so is somewhat puzzling, except that as speech is made up both of sound and of gesture, and our gestures are usually made with the right hand, it is not unreasonable to suppose that the speech centre should have grown up on that side of the brain which controls the right hand, which is, as you remember, the left hemisphere.