employed in vision; and forthly, an arrangement exists by means of which the eyes may be turned in the same direction by a system of muscles, so that binocular vision is possible. The eye may be compared to a photographic camera, and the transparent media corresponds to the photographic lens. In such a camera images of objects are thrown upon a ground-glass screen at the back of a box, the interior of which is painted black. In the eye, the camera proper is represented by the eyeball with its choroidal pigment, the screen by the retina, and the lens by the refracting media. In the ease of the camera, the screen is enabled to receive clear images of objects at different distances, by an apparatus for focusing. The corresponding contrivance in the eye is the 'accommodation.' The iris, which is capable of allowing more or less light to pass into the eye, corresponds with the different-sized diaphragms used in photographic apparatus." The "retina" of the eye, above mentioned, is a very sensitive membrane of nerve-matter lining the back of the eye, and being connected with the minute ends of the optic nerve; from the retina the impression is conveyed by the nerves to the brain.
The Sense of Taste
The sense of Taste, another evolved sense, manifests by means of certain nerves terminating in tiny cells of the tongue, known as "taste buds"; the latter are stimulated chemically by objects brought in contact with them, the impulse being conveyed to the nerves, and by them transmitted to the brain. Physiologists classify the sensations of taste into five classes, viz., sweet, sour, bitter, salty, and "hot" (as in the case of pepper, etc.).
The Sense of Smell
The sense of Smell, another evolved sense, manifests by means of delicate nerves terminating in the mucus membrane of the nostrils; the latter registering contact with minute particles of material objects entering the nostrils, and also registering differences in the chemical composition of such particles; the message of the nerve ends being transmitted to the brain. The particles of the "smelled" object must have actually entered the nostrils and have come in contact with these nerve ends in order to have been sensed. Mere nearness to the organ of smell is not sufficient—actual contact must be had, or we will smell nothing. We "smell" the rose only because minute particles of its substance are carried into our nostrils. We smell gas because some of its particles enter our nostrils.
The Sense of Hearing
The sense of Hearing, another evolved sense, manifest by means of delicate nerve terminating in the inner part of the ear. The eardrum, or "tympanum," vibrates in response to the air-vibrations or sound-waves reaching it from the outside; these vibrations are intensified, and the auditory nerve-ends take up the impression and pass it on to the brain. Sound-waves are sensed according to their characteristics of pitch, intensity, quality, and harmony, respectively.
The Offices of the Senses
The senses constitute the doors to the outside world, which when opened permit the entrance of messages from that world, but which, closed, bar the entrance of anything from without. Few of us ever stop to think how completely we are dependent upon these doors of the senses for our knowledge, our experience, and our objects of thought. We take it all for granted, and fail to perceive the importance of these senses. Only when one or more of the senses fail us do we begin to realize their importance, and the importance of sensations as a whole. It is only when we stop to think how completely shut in, and shutout, we would be if all of our senses were destroyed, that we begin to realize just how dependent we are upon the senses and sensation for our knowledge, our thoughts, our feelings, and our general mental life and being.
A leading psychologist has said: "Suppose a child of intelligent parents were ushered into the world without a nerve leading from his otherwise perfect brain to any portion of his body; with no optic nerve to transmit the glorious sensations from the eye, no auditory nerve to conduct the vibrations of the mother's voice, no tactile nerves to convey the touch of a hand, no olfactory nerve to rouse the brain with the delicate aroma of the orchards and the wild flowers in spring, no gustatory, thermal, or muscular nerves. Could such a child live, as the years rolled on, the books of Shakespeare and of Milton would be opened in vain before the child's eyes. The wisest men might talk to him with utmost eloquence all to no purpose. Nature could not whisper one of her inspiring truths into his deaf ear, could not light up that dark mind with a picture of the rainbow or of a human face. No matter how perfect might be the child's brain and his inherited capacity for mental activities, his faculties would remain for this life shrouded in Egyptian darkness. Perception could give memory nothing to retain, and thought could not weave her matchless fabrics without materials."
Another psychologist has said: "If it were possible for a human being to come into the world with a brain perfectly prepared to be the instrument of psychical operations, but with all the inlets to sensations closed, we have every reason to believe that the mind would remain dormant like a seed buried in the earth." Another says: "That the powers of the understanding would forever continue dormant were it not for the action of things external to the body, is a proposition now universally admitted by philosophers." Another says: "Apprehension by the senses supplies directly or indirectly the material of all human knowledge, or at least the stimulus necessary to develop every inborn faculty of the mind.'' Another says: "Even the highest ideas are slowly and gradually developed from the accumulation of sense experiences, and their truth is only guaranteed by the possibility of finding concrete examples for them in real existence. Another says: "The activity of the mind is just as much the result of its consciousness of external impressions, by which its faculties are called into play, as the life of the body is dependent upon the appropriation of nutrient materials and the constant influence of external forces." And another: "The senses are the means by which the mind obtains its knowledge of the outside world. Shut out from all direct communication with the outer world, it knows, and can know, nothing of what exists or is passing there, except what comes to it through the senses. Its knowledge of what is external to itself is therefore dependent upon the number, state, and condition of the sensory organs.''
In short: Psychologists hold that if a human being were born without sense organs, no matter how perfect a brain he might have, his life would be little more than that of the plant. He would exist in a dreamlike state, with only the faintest manifestations of consciousness. His consciousness would not be able to react in response to the impact of contact with the outside world, for there would be no such impact. And as consciousness depends almost entirely upon the impact of, or resistance to, outside impressions, his power of consciousness would be practically not called into play. He would perhaps be conscious of his own existence, but would probably never realize the fact fully, for he would have nothing else with which to compare himself, and his self-consciousness would not be aroused by the presence and pressure of the "not self." Such a man would not even have the memories of previous sensations, or experiences, to arouse or to heighten his consciousness or thought—and, consequently, he would have no imagination to use. He would be, to all intents and purposes, a "living corpse."
Helen Kellar had only two doors of sensation closed to her—the sense of Sight and that of Hearing. Touch, Taste, and Smell, however, were left to her; and each was quickened and heightened in order to help as far as possible to perform the work properly belonging to the defective senses. Her sense of Touch, especially, was wonderfully increased and quickened into activity; and through this channel her "self" was finally reached and communicated with by loving friends and teachers. The result in this particular case was almost a miracle—yet only two senses were missing. To get the full realization of the importance of the senses, one had but to think of the mental state of a Helen Kellar deprived from birth of the sense of Touch!
Arising from the above line of thought is the realization, that just as the world of the individual is decreased by each sense subtracted from him, so would his world be increased by each sense that might be added to him. And daring minds consider
