CHAPTER XII.

HOW THE EYE IS GUARDED.

[Sidenote: The eye seldom hurt.]

The eye, you know, is a very tender organ. It is therefore guarded thoroughly, and it is really very seldom hurt. But notice that it is just where it would be likely to be hurt if it were not thus guarded. It is right in the front part of the head. It must be there for the mind to use it in seeing. And it is much of the time open. You would suppose, then, that it must very often be struck and hit by things that are thrown about; but it is really very seldom hit so as to be hurt much.

The parts about the eye are often injured, but the eye itself generally escapes. We often see the eyelids and the cheek black and blue from a blow, and yet the tender and delicate eye is as sound as ever. People say, in such cases, that the eye is black and blue, but this is not so; the injury is all on the outside, and does not go into the eye.

[Sidenote: How it is guarded with the bones around it.]

Now let us see in what ways the eye is guarded. It is in a deep bony socket. There is bone all around it except in front. Then, too, see how the bones stand out all around it. The bone of the forehead juts over it. Below and to the outside stands out the cheek bone, and the nose is its wall on the inside. Now you can see that a blow with a stick would be very likely to strike upon some of these walls of bone, and the eye would then escape. They are real walls of defense to the eye. A stick can not hit the eye itself unless it goes with its end pointed to the eye. It must go in this way to avoid striking on these walls, or parapets of bone, by which the eye is surrounded.

But if the stick gets by these bony walls, it may not hurt the eye, after all. Perhaps you never thought what use there is in being able to wink so quickly. See what winking does. It shuts the eyelids over the eye, so that nothing can get into it unless it is something sharp enough to pierce through the lids. And a blow will not hurt the eye, if the lids are closed, unless it is hard enough to bruise it through the lids.

[Sidenote: The winking muscle.]

How quick is the working of that winking muscle! The moment that the eye sees any thing coming toward it that may injure it, this muscle shuts up the eye out of sight as quick as a flash. It hardly seems as if there was time for a message to go from the eye to the brain, and then another back from the brain to that muscle in the lids. But all this happens. The nerve of the eye tells the mind of the danger, and the mind sends a message to the winking muscle. This is done so quickly that whenever people speak of any thing as being done very quickly, they are very apt to say that it was done in the twinkling of an eye. This expression is used in the Bible in this way.

[Sidenote: The eye’s cushion of fat.]

But I have not told you all that this winking muscle does. It does something more than shut the eye in. It pushes it back in its socket, so that it is a little farther out of the way of a blow. And it does not push it right against the hard bone of the socket: there is a soft cushion of fat for it to press the eye against.

And this is not all. When the eye sees a blow coming, this muscle acts so strongly that it wrinkles the skin of the eyelids, and pulls down the eyebrow, and draws up the cheek, as you see here. Now see how this guards the eye. The cheek and the eyebrow are brought so near together that there is but little room for the blow to get at the eye; and even if it does, the wrinkled skin of the lids makes a cushion over it that breaks the force of the blow. You can see that the blow would be much more apt to do harm if the winking muscle merely brought the lids together. As it is, a blow commonly hits on the eyebrow or cheek, or both, while the eye is safe, shut up and pushed back in its cavern upon its cushion of fat. To see how much the bringing together of the cheek and eyebrow defends the eye, you must look at some one as he forcibly closes the eye, as represented in the figure. And if, at the same time, you put your finger on the parts, you will see how the cushions which all this wrinkling makes over the eye and about its socket defend it from harm.

[Sidenote: The winking muscles raise cushions over the eye to defend it.]

So you see that not only is the eye guarded by parapets of bone, but the busy winking muscle raises up cushions on them whenever the eye sees a blow coming. These cushions often save the bone from being cracked, and in this way also keep the eye from being hurt.

[Sidenote: The eyebrows.]

Of what use do you think the hairs on the eyebrows are? They are for good looks, you will say. But they are for something more than this; they are a defense to the eye. How this is I will explain to you. You know what the eaves of a house are for when there is no trough to the roof; they keep the rain from running down from the roof on the sides of the house. They make it drop off to the ground a little way from the house. Just so the hairy eyebrows make the sweat of the forehead drop off upon the cheek, instead of running down into the eye. The eyebrows, then, are the eaves of the roof of the eye’s house.

Perhaps you will ask what hurt the sweat would do if it should run down into the eye. It would be very disagreeable; and, besides this, it would irritate the eye and make it red. The eye would become inflamed.

[Sidenote: The eyelashes.]

The eyelashes, too, besides making the eye look well, are a defense to it. You know that there are often small things flying about in the air which we are not apt to see. If these fly against the eye, they generally hit against the eyelashes, and so are prevented from going into the eye.

[Sidenote: How the tears defend the eye.]

The tears, also, are a defense to the eye. If any thing happens to get by the eyelashes into the eye, how quick the tears flow to wash it out! Commonly the gland, or tear factory, only makes enough tears to keep the eye a little moist; but as soon as any thing gets into the eye and irritates it, the tear factory sets to work briskly, and sends down the tears abundantly. At the same time, the winking muscle keeps moving the lids, and generally what is in the eye is soon washed out.

Tears are flowing into the eye all the time. If they did not, the eyeball and the inside of the lids would become dry, and they would not move easily on each other. You would have to keep wetting them with water to prevent them from rubbing. The tear factory, which is just above the eye, continually sends down, through some little tubes or ducts, just enough tears to make the motion of the eye and the lids easy.

[Sidenote: The sink-drain of the eye.]

[Sidenote: In weeping the tears overflow their banks.]

But you will ask where the tears that are made go. They do not commonly run out over the lids, and they must go somewhere. I will tell you about this. If you look at the eyelids of any one, you can see in each lid a little hole at the end of the edge toward the nose. The tears go into these holes, and down through a duct that ends in the nose. This duct may be called the sink-drain of the eye, for the tears, after washing the eye, run off through it. The two little holes or mouths in the lids commonly take in all the tears as fast as they come to them; but when we cry, the tear factory makes tears so fast that these mouths can not take them all in. The tears, therefore, overflow their banks--the lids--and run down on the cheek.

_Questions._--Is the eye in a very exposed situation? Why is it seldom much hurt? Are the parts about it often hurt? Tell how the bones about the eye defend it. Of what use is winking? What is said about the quickness with which it is done? What else does the winking muscle do besides shutting the eye? What does it push the eye back upon? What else does this muscle do besides what has been mentioned? How does this defend the eye? On what does a blow aimed at the eye commonly hit? Of what use are the hairs on the eyebrows? What harm would the sweat do if it ran down into the eye? Of what use are the eyelashes? In what ways do the tears prevent the eyes from being injured? Where do the tears go to from the eye? What happens when one cries?