=The Eyes: Eye-strain.=—Of all the misfortunes that could befall a human being, the loss of sight is probably the greatest, and yet no organ of the body is so constantly abused as the eye. The trouble is that the possessor of the normal eye does not take into consideration that in all near work, as in reading, writing, sewing, etc., the eye is actively engaged as well as the hands and brain, and that the eye only is at rest when looking into space or when closed. =Description of the Visual Apparatus.=—The eyeball is contained and protected in a bony cavity, formed by the bones of the face and skull, and is supported by a cushion of fat and other tissues. It is held in place by its membranes and muscles, by which it is also moved. It is further protected by the eyelids, the eyebrows, and the eyelashes. The eyebrows protect the eyes from dust and perspiration and shade the eyes. The eyelids are lined by a very delicate mucous membrane, called the conjunctiva. They are maintained in close apposition to the eyeball by atmospheric pressure. The tears are secreted by the lacrimal gland, which is at the upper and outer angle of the orbit. The lubrication by the tears and the mucus secreted by the conjunctiva cause them to move smoothly and without friction. An important function of the lids is to distribute the tears over the front of the eyeball, and by incessant winking to free the front of the eye from dust and to keep it moist. The conjunctiva is continuous with the mucous membrane of the nose and mouth. Hence, in inflammation of the nasal mucous membrane, as in an ordinary cold in the head or influenza, the conjunctiva is liable to become very much congested or inflamed. The _eyeball_ is spherical in form, having the segment of a smaller and much more prominent sphere ingrafted on its anterior part. The segment of the larger sphere, which forms about five-sixths of the globe, is opaque, and forms the sclerotic coat, the so-called “white” of the eye. The smaller sphere, which forms the remaining sixth, is transparent, and is formed by the cornea. The _iris_ is a circular contracting membrane, suspended from the edges of the cornea, in front of the eye like a curtain. The iris gives color to the eye, and when we say that an eye is blue or brown, we mean that is the color of the iris. The iris is freely movable, and, according as to whether it dilates or contracts, there is an alteration in the size of the central aperture, called the pupil. The chief function of the iris is to regulate the quantity of light admitted to the interior of the eye. In a very strong light the pupil quickly contracts, shutting out the excessive light, while in a subdued light the pupil dilates, thus allowing more light to enter. When looking at a distance or when looking languidly into space, the pupil dilates.