Touch tells whether anything is hard, or rough, or round, or square, or has other qualities and shapes.
Second, when anything touches the bare nerves or hurts the cells, we feel a pain. We can feel a pain anywhere in the body. Pain tells us if we are being harmed. If we had no feeling of pain, we might be killed before we could know of our danger. Pain warns us away from danger.
Third, we can feel heat and cold. Anything very hot or very cold, however, makes only a pain and gives no feeling either of cold or of heat.
164. Sight.—We see with our eyes. An eye is a hollow ball. In its front is a clear window. Behind the window is a round curtain with a round hole in its middle. When we speak of the color of the eye, we mean the color of this curtain. Light passes through the hole in the curtain and falls upon some nerves in the back of the eyeballs. There it forms a picture like a photograph. The nerves carry this picture to the brain, and we see it.
The human eye.
| a bony case of the eye. | e lining or seeing part of the eye. |
| b muscle to move the eye. | f eyelid. g colored curtain or iris. |
| c and d coverings of the eye. | h and i clear windows of the eye. |
165. Movements of the eyes.—We can turn our eyes so as to look in any direction. Sometimes a person has one eye turned sidewise. Such a person is cross-eyed, and sees well out of only one eye at a time. Glasses may help the eyes, but sometimes a surgeon has to cut a tiny muscle.
166. Coverings of the eyes.—The eyeballs lie in a bony case, upon a soft bed of fat. In front each is covered with two lids. We can shut the lids to keep out dust and insects. When we are sleepy, they come together and cover the eyes. Little hairs at their edges help to keep out the dust.