The Special Senses : Part 1

Hygienic Physiology: with Special Reference to the Use of Alcoholic Drinks and Narcotics
by Joel Dorman Steele, Ph.D.

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"See how yon beam of seeming white Is braided, out of seven-hued light; Yet in those lucid globes no ray By any chance should break astray. Hark, how the rolling surge of sound, Arches and spirals circling round, Wakes the hushed spirit through thine ear With music it is heaven to hear."

- Holmes.

"Let us remember that if we get a glimpse of the details of natural phenomena, and of those movements which constitute life, it is not in considering them as a whole, but in analyzing them as far as our limited means will permit. In the vibrations of the globe of air which surrounds our planet, as in the undulations of the ether which fills the immensity of space, it is always by molecules which are intangible for us, put in motion by nature, always by the infinitely little, that she acts in exciting the organs of sense, and she has modeled these organs in a proportion which enables them to partake in the movement which she impresses upon the universe. She can paint with equal facility on a fraction of a line of space on the retina, the grandest landscape or the nervelets of a rose leaf; the celestial vault on which Sirius is but a luminous point, or the sparkling dust of a butterfly's wing; the roar of the tempest, the roll of thunder, the echo of an avalanche, find equal place in the labyrinth whose almost imperceptible cavities seem destined to receive only the most delicate sounds."

The Special Senses

1. Touch

Description. - Touch is sometimes called the "common sense," since its nerves are spread over the whole body. It is most delicate, however, in the point of the tongue and the tips of the fingers. The surface of the cutis is covered with minute, conical projections called papilla. Each one of these papilla contains its tiny nerve twigs, which receive the impression and transmit it to the brain, where the perception is produced.

Uses. - Touch is the first of the senses used by a child. By it we obtain our idea of solidity, and throughout life rectify all other sensations. therefore, when we see anything curious, our first desire is to handle it.

The sensation of touch is generally relied upon, yet, if we hold a marble in the manner shown in Fig. 57, it will seem like two marbles; and if we touch the finger. Therefore crossed to our tongue, we should seem to feel two tongues. Again, if we close our eyes and let another person move one of our fingers over a plane surface, first lightly, then with greater pressure, and then lightly again, we should think the surface concave.

This organ is capable of wonderful cultivation. The physician acquires by practice the tactus eruditus, or learned touch, which is often of great service, while the delicacy of touch possessed by the blind almost compensates the loss of the absent sense.

2. Taste

Description. - This sense is located in the papilla of the tongue and palate. These papillae start up when tasting, as you can see by placing a drop of vinegar on another person's tongue, or your own before a mirror. The velvety look of this organ is given by hair-like projections of the cuticle upon some of the papille. They absorb the liquid to be tasted, and convey it to the nerves. The back of the tongue is most sensitive to salt and bitter substances, and, as this part is supplied by the ninth pair of nerves, in sympathy with the stomach, such flavors, by sympathy, often produce vomiting. The edges of the tongue are most sensitive to sweet and sour substances, and as this part is supplied by the fifth pair of nerves, which also goes to the face, an acid, by sympathy, distorts the countenance.

The Use of the Taste was originally to guide in the selection of food; but this sense has become so depraved by condiments and the force of habit that it would be a difficult task to tell what are one's natural tastes.

3. Smell

Description. - The nose, the seat of the sense of smell, is composed of cartilage covered with muscles and skin, and joined to the skull by small bones. The nostrils open at the back into the pharynx, and are lined by a continuation of the mucous membrane of the throat. The olfactory nerves enter through a sieve-like, bony plate at the roof of the nose, and are distributed over the inner surface of the two olfactory chambers. The object to be smelled need not touch the nose, but tiny particles borne on the air enter the nasal passages.

The Uses of the sense of smell are to guide us in the choice of our food, and to warn us against bad air, and unhealthy localities.

4. Hearing

Description. - The ear is divided into the external, middle, and internal ear.

1. The External Ear is a sheet of cartilage curiously folded for catching sound. The auditory canal, B, or tube of this ear trumpet, is about an inch long. Across the lower end is stretched the membrane of the tympanum or drum, which is kept soft by a fluid wax.

2. The Middle Ear is a cavity, at the bottom of which is the Eustachian tube, G, leading to the mouth. Across this chamber hangs a chain of three singular little bones, C, named from their shape the hammer, the anvil, and the stirrup. All together these tiny bones weigh only a few grains, yet they are covered by a periosteum, are supplied with blood vessels, and they articulate with perfect joints (one a ball-and-socket, the other a hinge), having synovial membranes, cartilages, ligaments, and muscles.

3. The Internal Ear, or labyrinth, as it is sometimes called from its complex character, is hollowed out of the solid bone. In front, is the vestibule or antechamber, A, about as large as a grain of wheat; from it open three semicircular canals, D, and the winding stair of the cochlea, or snail shell, E. Here expand the delicate fibrils of the auditory nerve. Floating in the liquid which fills the labyrinth is a little bag containing hair-like bristles, fine sand, and two ear stones. All these knocking against the ends of the nerves, serve to increase any impulse given to the liquid in which they lie. Finally, to complete this delicate apparatus, in the cochlea are minute tendrils, named the fibers of Corti, from their discoverer. These are regularly arranged, - the longest at the bottom, and the shortest at the top. Could this spiral plate, which coils two and a half times around, be unrolled and made to stand upright, it would form a beautiful microscopic harp of three thousand strings. If it were possible to strike these cords as one can the keyboard of a piano, he could produce in the mind of the person experimented upon every variety of tone which the ear can distinguish.