. Elements of biology; a practical text-book correlating botany, zoology, and human physiology. Biology. 426 HUMAN PHYSIOLOGY that the image is inverted. The same is true of the image on the retina. By means of this image thrown on the sensory layer, the rod and cone cells of the retina are stimulated and the image is transmitted to the forebrain. We must remember that the optic nerve crosses under the brain so that images formed in the right eye are received by the left half of the forebrain, and vice versa, '^ Effects of Drinks containing Alcohol upon the Eye. — Through its influence upon th
. Elements of biology; a practical text-book correlating botany, zoology, and human physiology. Biology. 426 HUMAN PHYSIOLOGY that the image is inverted. The same is true of the image on the retina. By means of this image thrown on the sensory layer, the rod and cone cells of the retina are stimulated and the image is transmitted to the forebrain. We must remember that the optic nerve crosses under the brain so that images formed in the right eye are received by the left half of the forebrain, and vice versa, '^ Effects of Drinks containing Alcohol upon the Eye. — Through its influence upon the nerves and the muscles, the continued and too free use of alcohol renders the eye unsteady and its adjustment uncertain; the small blood vessels become dilated, and the eyes are blood-shot and often inflamed. The optic nerve is frequently affected, causing dimness of vision, and specific diseases of parts of the eye may result, such as cataract and disorders of the retina. The confirmed inebriate is the victim of diseased conditions in which the sight becomes untrustworthy. He sees horrible visions, frightful, venomous creatures appear to threaten him, and he is haunted by specters. Under his imaginary suffering he may be- come a raving maniac, and repeated attacks of the disease are likely to prove ; — Macy, Physiology. The Blind Spot. — Although the eye is an accurate organ for sight, yet one part of the retina is not provided with sensory cells. This area, called the blind spot, marks the point within the eye where the optic nerve enters and spreads out in a very thin layer over the surface of the retina. How THE Voice is Produced.—The voice box, or larynx, is well known to every boy as his " Adam's ; It consists of a box of movable cartilages, joined in such a way to each other and to muscles so that by contraction of certain muscles, the form of the larynx is changed. Within the larynx are stretched two narrow pads of elastic tissue cal
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