Never insert into the ear ca.n.a.l the corners of towels, ear spoons, the ends of toothpicks, hairpins, or any other pointed instruments. It is a needless and dangerous practice, usually causing, in time, some form of inflammation. The abrasion of the skin in the ca.n.a.l thus produced affords a favorable soil for the growth of vegetable parasites.

[Ill.u.s.tration: Fig. 143.--Diagram of the Middle and Internal Ear.]

This, in turn, may lead to a chronic inflammation of the ca.n.a.l and of the tympanic membrane. Again, there is always risk that the elbow may be jogged and the instrument pushed through the drum-head. There is, of course, a natural impulse to relieve the itching of the ear. This should be done with the tips of the fingers or not at all.

The popular notion that something should be put into the ear to cure toothache is erroneous. This treatment does not cure a toothache, and may lead to an injury to the delicate parts of the ear. A piece of absorbent cotton, carefully inserted into the ear, may be worn out of doors, when the cold air causes pain, but should be removed on coming into the house.

Frequent bathing in the cold water of ponds and rivers is liable to injure both the ears and the general health. In salt-water bathing, the force of the waves striking against the ears often leads to earache, long-continued inflammation, or defective hearing; to diminish this risk, insert into the ears a small plug of absorbent cotton.

The ears are often carelessly exposed to cold water and inclement weather.

Very cold water should never be used to bathe the ears and nostrils. Bathe moderately and gently in lukewarm water, using a wash-rag in preference to a sponge; dry gently and thoroughly. Children's ears are often rudely washed, especially in the auditory ca.n.a.l. This is not at all necessary to cleanliness, and may result in a local inflammation.

Never shout suddenly in a person's ear. The ear is not prepared for the shock, and deafness has occasionally resulted. A sudden explosion, the noise of a cannon, may burst the drum-head, especially if the Eustachian tube be closed at the time. During heavy cannonading, soldiers are taught to keep the mouth open to allow an equal tension of air.

[Ill.u.s.tration: Fig. 144.--Section of Cochlea.

From A straight downwards is the direction of the central column, to which E points. B points to the projecting ridge, almost dividing the ca.n.a.l of the tube into an upper compartment (D), and a lower (C).]

Insects may gain entrance to the ears and occasion annoyance, pain, and fright, perhaps leading to vomiting, even to convulsions, with nervous children. A lighted lamp held at the entrance of the ear will often induce the offending insect to crawl out towards the light. A few drops of warm water, sweet oil, or mola.s.ses, dropped into the ear, will help remove the intruder.

When a discharge occurs from the ears, it is not best to plug them with cotton wads. It only keeps in what should be got rid of. Do not go to sleep with the head on a window sill or in any position, with the ears exposed to draughts of cold or damp air.

No effort should be made to remove the ear wax unless it acc.u.mulates unduly. The skin of the ca.n.a.l grows outward, and the extra wax and dust will be naturally carried out, if let alone. Never employ any of the many articles or "drops," advertised to cure deafness. Neuralgic pain in the ca.n.a.l, usually cla.s.sed as earache, may be due to decayed or improperly filled teeth.

Quinine, so generally used in its many preparations for malaria, causes a peculiar ringing or buzzing in the ears. This is a warning that it should be taken in smaller doses, or perhaps stopped for a time. In some cases quinine may produce temporary deafness.

The practice of snuffing up cold water into the nostrils is occasionally followed by an acute inflammation of the middle ear, some of the water finding its way through the Eustachian tube into this part of the organ of hearing. The nasal douche, so often advised as a home remedy for nasal catarrh, should be used only with great caution, and always in accordance with detailed directions from a physician.

348. Effect of Tobacco upon the Hearing. The sense of hearing is often injured by the use of tobacco. The irritating smoke filling all the inner cavity of the mouth and throat, readily finds its way up the Eustachian tube, dries the membrane, and irritates or inflames the delicate mechanism of the inner ear. Thus may be produced a variety of serious aural disturbances, such as unnatural noises, whistling, and roaring, followed oftentimes by a partial loss of hearing.

Hearing may be impaired by the use of alcoholic beverages. Alcohol inflames the mucous membrane of the throat, then by its nearness the lining of the Eustachian tube, and finally may injure the delicate apparatus of the internal ear.

Additional Experiments.

Experiment 162. Use a small pair of wooden compa.s.ses, or an ordinary pair of dividers with their points guarded by a small piece of cork. Apply the points of the compa.s.ses lightly and simultaneously to different parts of the body, and ascertain at what distance apart the points are felt as two. The following is the order of sensibility: tip of tongue, tip of the middle finger, palm, forehead, and back of hand.

Experiment 163. Test as in preceding experiment the skin of the arm, beginning at the shoulder and pa.s.sing downwards. Observe that the sensibility is greater as one tests towards the fingers, and also in the transverse than in the long axis of the limb. In all cases compare the results obtained on both sides of the body.

Experiment 164. By means of a spray-producer, spray the back of the hand with ether, and observe how the sensibility is abolished.

Experiment 165. Touch your forehead with your forefinger; the finger appears to feel the contact, but on rubbing the forefinger rapidly over the forehead, it is the latter which is interpreted as "feeling" the finger.

Experiment 166. Generally speaking, the sensation of touch is referred to the cutaneous surfaces. In certain cases, however, it is referred even beyond this. Holding firmly in one hand a cane or a pencil, touch an object therewith; the sensation is referred to the extremity of the cane or pencil.

If, however, the cane or pencil be held loosely in one's hand, one experiences two sensations: one corresponding to the object touched, and the other due to the contact of the rod with the skin. The process of mastication affords a good example of the reference of sensations to and beyond the periphery of the body.

Experiment 167. Prepare a strong solution of sulphate of quinine with the aid of a little sulphuric acid to dissolve it (_bitter_), a five-per-cent solution of sugar (_sweet_), a ten-per-cent solution of common salt (_saline_), and a one-per-cent solution of acetic acid (_acid_). Wipe the tongue dry, and lay on its tip a crystal of sugar. It is not tasted until it is dissolved.

Experiment 168. Apply a crystal of sugar to the tip, and another to the back of the tongue. The sweet taste is more p.r.o.nounced at the tip.

Experiment 169. Repeat the process with sulphate of quinine in solution. It is scarcely tasted on the tip, but is tasted immediately on the back part of the tongue. Test where salines and acids are tasted most acutely.

Experiment 170. _To ill.u.s.trate the muscular sense_. Take two equal iron or lead weights; heat one and leave the other cold. The cold weight will feel the heavier.

Experiment 171. Place a thin disk of _cold_ lead, the size of a silver dollar, on the forehead of a person whose eyes are closed; remove the disk, and on the same spot place two warm disks of equal size. The person will judge the latter to be about the same weight, or lighter, than the single cold disk.

Experiment 172. Compare two similar wooden disks, and let the diameter of one be slightly greater than that of the other. Heat the smaller one to over 120 F., and it will be judged heavier than the larger cold one.

Experiment 173. _To ill.u.s.trate the influence of excitation of one sense organ on the other sense organs_. Small colored patches the shape and color of which are not distinctly visible may become so when a tuning-fork is kept vibrating near the ears. In other individuals the visual impressions are diminished by the same process.

On listening to the ticking of a watch, the ticking sounds feebler or louder on looking at a source of light through gla.s.ses of different colors.

If the finger be placed in cold or warm water the temperature appears to rise when a red gla.s.s is held in front of the eyes.

Experiment 174. _Formation of an inverted image on the retina_.

Take a freshly removed ox-eye; dissect the sclerotic from that part of its posterior segment near the optic nerve. Roll up a piece of blackened paper in the form of a tube, black surface innermost, and place the eye in it with the cornea directed forward. Look at an object--_e.g._, a candle-flame--and observe the inverted image of the flame shining through the retina and choroid, and notice how the image moves when the candle is moved.

Experiment 175. Focus a candle-flame or other object on the ground-gla.s.s plate of an ordinary photographic camera, and observe the small inverted image.

Experiment 176. _To ill.u.s.trate spherical aberration_. Make a pin-hole in a blackened piece of cardboard; look at a light placed at a greater distance than the normal distance of accommodation. One will see a radiate figure with four to eight radii. The figures obtained from opposite eyes will probably differ in shape.

Experiment 177. Hold a thin wooden rod or pencil about a foot from the eyes and look at a distant object. Note that the object appears double. Close the right eye; the left image disappears, and _vice versa_.

Experiment 178. _To show the movements of the iris_. It is an extremely beautiful experiment, and one that can easily be made. Look through a pin-hole in a card at a uniform white surface as the white shade of an ordinary reading-lamp. With the right eye look through the pin-hole, the left eye being closed. Note the size of the (slightly dull) circular visual field. Open the left eye, the field becomes brighter and smaller (contraction of pupil); close the left eye, after an appreciable time, the field (now slightly dull) is seen gradually to expand. One can thus see and observe the rate of movements of his own iris.

[Ill.u.s.tration: Fig. 145.]

Experiment 179. _To show the blind spot_. The left eye being shut, let the right eye be fixed upon the cross as in Fig. 145. When the book is held at arm's length, both cross and round spot will be visible; but if the book be brought to about 8 inches from the eye, the gaze being kept steadily upon the cross, the round spot will at first disappear, but as the book, is brought still nearer both cross and round spot will again be seen.

Experiment 180. _To ill.u.s.trate the duration of retinal impressions_. On a circular white disk, about halfway between the center and circ.u.mference, fix a small, black, oblong disk, and rapidly rotate it by means of a rotating wheel. There appears a ring of gray on the black, showing that the impression on the retina lasts a certain time.

[Ill.u.s.tration: Fig. 146.--Optic Disks.

The disk A, having black and white sectors, when rotated rapidly gives an even gray tint as in B.]

Experiment 181. Mark off a round piece of cardboard into black and white sectors as in A (Fig. 146). Attach it so as to rotate it rapidly, as on a sewing machine. An even gray tint will be produced as in B.

Experiment 182._To ill.u.s.trate imperfect visual judgments_. Make three round black dots, A, B, C, of the same size, in the same line, and let A and C be equidistant from B. Between A and B make several more dots of the same size. A and B will then appear to be farther apart than B and C.

[Ill.u.s.tration: * * * * * * *

A B C ]

For the same reason, of two squares absolutely identical in size, one marked with alternately clear and dark cross-bands, and the other with alternately clear and dark upright markings, the former will appear broader and the latter higher than the other.

Experiment 183. Make on a white card two squares of equal size.

Across the one draw _horizontal_ lines at equal distances, and in the other make similar _vertical_ lines. Hold them at some distance. The one with horizontal lines appears higher than it really is, while the one with vertical lines appears broader, i.e., both appear oblong.