By Prof. David Webster, M.D.

"The light of the body is the eye." Of all our senses, sight, hearing, touch, taste, and smell, the sight is that which seems to us the most important. Through the eye, the organ of vision, we gain more information and experience more pleasure, perhaps, than through any or all our other organs of sense. Indeed, we are apt to depreciate the value of our other senses when comparing them to the eyesight. It is not uncommon to hear a person say, "I would rather die than be blind." But no one says, "I would rather die than lose my hearing." As a matter of fact, the person who is totally blind generally appears to be more cheerful, happier, than one who is totally deaf. Deaf mutes are often dull, morose, quick tempered, obstinate, self-willed, and difficult to get along with, while the blind are not infrequently distinguished for qualities quite the reverse. It is worthy of remark that the eye is that organ of sense which is most ornamental as well as useful, and the deprivation of which constitutes the most visible deformity. But it is unnecessary to enter into a comparison of the relative value of our senses or the relative misfortune of our loss of any one of them.

We need them all in our daily struggle for existence, and it is necessary to our physical and mental well-being, as well as to our success in life, that we preserve them all in as high a degree of perfection as possible. We must not lose sight of the fact that all our organs of sense are parts of one body, and that whatever we do to improve or preserve the health of our eyes cannot do harm to any other organ. We shall be able to "take care of our eyes" more intelligently if we know something of their structure and how they perform their functions. The eye is a hollow globe filled with transparent material and set in a bony cavity of the skull, which, with the eyelids and eyelashes, protect it from injury. It is moved at will in every direction by six muscles which are attached to its surface, and is lubricated and kept moist by the secretions of the tear gland and other glands, which secretions, having done their work, are carried down into the nose by a passage especially made for the purpose - the tear duct.

We are all familiar with the fact that our eyes are "to see with," but in order to be able to take care of our eyes intelligently, it is necessary to understand as far as possible how to see with them.

The Back Wall Of The Eye

It is a remarkable fact that every object we see has its picture formed upon the back wall of our eyes. The eye is a darkened chamber, and the whole of the front part of it acts as a lens to bring the rays of light coming from objects we wish to see to a focus on its back wall, thus forming a picture there as distinct as the picture formed in the camera obscura of the photographer. This has not only been proved by the laws of optics, but has been actually demonstrated in the eyes of rabbits and other animals. Experimenters have held an object before the eye of a rabbit for a few moments, and have then killed the animal and removed the eye as quickly as possible, and laid its back wall bare, and have distinctly seen there the picture of the object upon which the eye had been fixed. It is a truly wonderful fact that these pictures upon the back wall of the eye can be changed so rapidly that the picture of the object last looked at disappears in an instant and makes way for the picture of the next. We know that the picture formed on the back wall of the eye is carried back to the brain by the optic nerve, but there our knowledge stops. Science cannot tell us how the brain, and through it the mind, completes the act of seeing.

It is there that the finite and the infinite touch, and, as our minds are finite, we cannot comprehend the infinite.

But there is enough that we can understand, and it shall be my endeavor in this paper to make some plain statements that will help as a guide in the preservation of those wonderful and useful organs.

Far And Near Sightedness

We have to use our eyes for near and far distant vision. In gathering pictures of distant objects the normally shaped eye puts forth little or no effort. It is the near work, such as reading, sewing, or drawing, that puts a real muscular strain upon the eyes. There are certain rules that apply to the use of the eyes for such near work regardless of the age of the person.

Reading

1. In reading, a book or newspaper should be held at a distance of from ten to fifteen inches from the eyes. It is hardly necessary to caution anybody not to hold the print further away than fifteen inches. The only objection to holding ordinary print too far away is that in so doing the pictures formed on the back wall of the eye are too small to be readily and easily perceived, and the close attention consequently necessary causes both the eyes and the brain to tire. Most persons quickly find this out themselves, and the tendency is rather to hold the book too near, for the nearer the object to the eye, the larger its picture upon the retina, or back eye wall. But here we encounter another danger. The nearer the object the eyes are concentrated upon, the greater the muscular effort necessary; so that by holding the book too near, the labor of reading is greatly increased, and the long persistence in such a habit is likely to produce weak eyes, and may, in some instances, lead to real near-sightedness. When children are observed to have acquired this habit and cannot be persuaded out of it, they should always be taken to a physician skilled in the treatment of the eye for examination and advice.

A little attention at such a time may save them from a whole lifetime of trouble with their eyes. Of course, the larger the print, the farther it may be held from the eyes.

Position

2. The position of the person with regard to the light should be so that the latter will fall upon the page he is reading, and not upon his eyes. It is generally considered most convenient to have the light shine over the left shoulder, so that in turning the leaves of the book, the shadow of the hand upon the page is avoided. It is not always possible to do this, however, and, at the same time, to get plenty of light upon the page. When one finds himself compelled to face the light in reading, or in standing at a desk bookkeeping, he should always contrive to shade his eyes from a direct light. This may be done with a large eye shade projecting from the brow. A friend of mine, a physician, is very fond of reading by a kerosene lamp, the lamp being placed on a table by his side, and the direct light kept from his eyes by means of a piece of cardboard stuck up by the lamp chimney.

Proper Light

3. The illumination should always be sufficient. Nothing is more injurious to the eyes than reading by a poor light. Many persons strain their eyes by reading on into the twilight as long as they possibly can. They become interested and do not like to leave off. Some read in the evening at too great a distance from the source of light, forgetting that the quantity of light diminishes as the square of the distance from the source of light increases. Thus, at four feet, one gets only one-sixteenth part of the light upon his page that he would at one foot. It is the duty of parents and others who have charge of children to see to it that they do not injure their eyes by reading by insufficient light, either daylight or artificial light. There is a common notion that electric light is bad for the eyes. The only foundation I can think of for such a notion is that it is trying to the eyes to gaze directly at the bright electric light. It is bad to gaze long at any source of light, and the brighter the source of light gazed at, the worse for the eyes, the sun being the worst of all. I have seen more than one person whose eyes were permanently injured by gazing at the sun, during an eclipse or otherwise.

As a matter of fact, nothing short of sunlight is better than the incandescent electric light to read by or to work by.

Reading In Bed

As to reading while lying down in bed or on a lounge, I can see no objection to it so far as the eyes are concerned, provided the book is held in such a position that the eyes do not have to be rolled down too far. Unless the head is raised very high by pillows, however, it will be found very fatiguing to hold the book high enough, not to mention the danger of falling asleep, and of upsetting the lamp or candle, and thus setting the bed on fire. Many persons permanently weaken their eyes by reading to pass away the tedious hours during recovery from severe illness. The muscles of the eyes partake of the general weakness and are easily overtaxed. Persons in this condition may be read to, but should avoid the active use of their own eyes.

Reading In Rail Cars

Reading while in the rail cars or in omnibuses is to be avoided. The rapid shaking, trembling or oscillating motion of the cars makes it very difficult to keep the eyes fixed upon the words, and is very tiresome. I have seen many persons who attributed the failure of their eyes to the daily habit of reading while riding to and from the city. Children should be cautioned against reading with the head inclined forward. The stooping position encourages a rush of blood to the head, and consequently the eyes become congested, and the foundations for near-sightedness are laid.

(To be continued.)

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From a paper by David Webster. M.D., professor of ophthalmology in the New York Polyclinic and surgeon to the Manhattan Eye and Ear Hospital, New York.

Testing Indigo Dyes

The author deals with the question whether a sample of goods is dyed with indigo alone or with a mixture of indigo and other blue coloring matters. His method may be summarized as follows: Threads of the material in question should give up no coloring matter to boiling water. Alcohol at 50 and at 95 per cent. (by volume) ought to extract no color, even if gently warmed (not boiled). Solution of oxalic acid saturated in the cold, solution of borax, solution of alum at 10 per cent., and solution of ammonium molybdate at 331/ per cent. ought not to extract any coloring matter at a boiling heat. The borax extract, if subsequently treated with hydrochloric acid, should not turn red, nor become blue on the further addition of ferric chloride. Solutions of stannous chloride and ferric chloride with the aid of heat ought entirely to destroy the blue coloring matter. Glacial acetic acid on repeated boiling should entirely dissolve the coloring matter. If the acetic extracts are mixed with two volumes of ether and water is added, so as to separate out the ether, the water should appear as a slightly blue solution, the main bulk of the indigo remaining in suspension at the surface of contact of the ethereal and watery stratum.

This acid watery stratum should be colorless, and should not assume any color if a little strong hydrochloric acid is allowed to fall into it through the ether. No sulphureted hydrogen should be evolved on boiling the yarn or cloth in strong hydrochloric acid. On prolonged boiling, supersaturation with strong potassa in excess, heating and adding a few drops of chloroform, no isonitrile should be formed. - W. Lenz.