The ear-drum performs a two-fold office; for while it aids in the transmission of sound from without to the internal ear, it at the same time modifies the intensity of sound. This softening of the sound is effected by the relaxation of a muscle when sounds are so acute as to be painful; but when listening to low sounds, the drum is rendered tense by the contraction of this muscle, and the sounds become, by this means, more audible. The vibrations made on the drum are transmitted by the tympanum—an irregular bony cavity—to the internal ear, which is filled with a watery fluid. In this fluid the filaments of the auditory nerve terminate, which receive and transmit the sound to the brain.
The ear has the power of judging of the direction from which sound comes, as is strikingly exemplified in the fact that when horses or mules march in company at night, those in front direct their ears forward, and those in the rear turn them backward, while those in the center turn them laterally or across, the whole troop seeming to be actuated by a feeling to watch the common safety. This is also illustrated by four or six horse teams, and is a fact with which coachmen are familiar. It is further illustrated by the dog, and many other animals. The external ear of man is likewise furnished with muscles; and savages are said to have the power of moving or directing their ears at pleasure, like a horse, to catch sounds as they come from different directions; but few men in civilized life retain this power.
The acuteness of this sense in men and animals, other things being equal, depends upon the size of the ear. In timid animals, as the hare and the rabbit, the ear is very large. They are thus apprized of the approach of an enemy in time to flee to a place of safety.
The ear-trumpet—which is a tube wide at one end, where the sound enters, and narrow at the other, where the ear is applied—is constructed on this principle, its sides being so curved that, according to the law of reflection, all the sound which enters it is brought to a focus in the narrow end. It thus increases many fold the intensity of a sound which reaches the ear through it, and enables a person who has become deaf to common conversation to mix again with pleasure in society. The concave hand held behind the ear answers in some degree the purpose of an ear-trumpet.
The Ear of Dionysius, in the dungeons of Syracuse, was a notorious instance of a sound-collecting surface. The roof of the prison was so formed as to collect the words, and even whispers, of the unhappy prisoners, and to direct them along a hidden conduit to where the tyrant sat listening.
Acuteness of hearing requires the healthy action of the brain, and particularly of that portion of it from which the auditory nerve proceeds, combined with perfection in the structure and functions of the different parts of the ear. The best method, then, of retaining and improving the hearing, is to observe well the general laws of health, and particularly to avoid every thing that will in the least impair the structure or healthy action of the parts immediately concerned in the exercise of this function. Inflammatory fevers, affections of the brain, and injuries upon the head, are among the more common causes of imperfect hearing. Hence the impropriety of striking children upon the head in correcting them, whether in the family or in the school. The instances are not few in which deafness, and the impairing of the mental faculties, have resulted from that barbarous practice familiarly known as "boxing the ears." This inhuman practice is likely to result in injury to the drum of the ear, either in thickening this membrane, or in diminishing its vibratory character. Inflammation of the ear-drum, either acute or chronic, is the common cause of its increased thickness. How often this is produced by blows, the reader may judge. Diminution of the vibratory character of the ear-drum may result from an accumulation of wax upon its outer surface. In such cases chronic inflammation of the parts is not unfrequently the result of the injudicious practice of attempting its removal by introducing the heads of pins into the ear.
This wax, it should be known, is designed to subserve an important end; for the tube leading from the external ear, being, like the nose, constantly open, is liable to the entrance of foreign bodies, such as dust, insects, and the like. But, fortunately, it is not left without the means of defense; for on its inside there are numerous fine bristles, which, interlacing each other, interpose a barrier to the entrance of every thing but sound. Moreover, between the roots of these hairs there are numerous little glands, that secrete a nauseous, bitter wax, which, by its offensiveness, either deters insects from entering, or entangles them and prevents their advance in case they do enter. This wax, then, is very serviceable. But its usefulness does not stop here. When the ear becomes dry from a deficiency of it, the hearing becomes imperfect, as also when it is thin and purulent. This wax not unfrequently becomes hard and obstructs the tube, causing less or more deafness. But this form of deafness may be easily cured, even though it has existed for years; for, having softened the accumulations of viscid wax by dropping animal oil into the ear, they may be removed by the injection of warm soap-suds, which is an effectual and safe remedy.
The sense of hearing is perhaps as susceptible of cultivation as any of the senses. The Indian in the forest, who is accustomed to listen to the approach of his enemies or of his prey, acquires such acuteness of hearing as to be able to detect sounds that would be inaudible to persons living amid the din of civilized life. The blind, also, who of necessity are led to rely more upon this sense than seeing persons, excel in the acuteness of their hearing. They recognize their acquaintances by the exercise of this sense as readily as persons usually do by that of sight, an attainment which very few seeing persons make, and yet one that is perhaps within the reach of ninety-nine persons in every hundred. The blind judge with great accuracy the distance of persons in conversation, of carriages in motion, and of all sonorous bodies whose vibrations reach their ears. They even estimate with remarkable correctness the distance and height of buildings by the reflection or interception of sound. It is in consequence of the acuteness of this sense, acquired by careful cultivation, that the blind, as a class, have become so generally and justly distinguished for their pre-eminence in instrumental music. This enables them also to cultivate vocal music with more than ordinary success.
The due cultivation of the sense of hearing will contribute vastly to promote our intellectual and moral well-being. If it be true, as we are told it is by those who have been engaged in teaching both the deaf and the blind, that the absence of hearing is even a more formidable impediment to the communication of knowledge than that of sight, we must infer that all imperfections of the organ of hearing itself, or in the manner of using it, must correspondingly lessen the accuracy of the knowledge we receive through that organ. The meaning of language very often is conveyed not so much by the words themselves as in the tones of voice in which the words are uttered. If, therefore, the hearing be indistinct, or there be no habit formed of careful attention to the inflections of sound, the impressions received from what we hear must often be inaccurate. Our speech, too, will be far less agreeable, and be inefficient, even if it be not positively inarticulate. We owe it to others, no less than to ourselves, then, to cultivate the powers of the voice—the common instrument that God has given us for the interchange of thought, sentiment, and feeling, and which, though so common, is the most perfect of all instruments for the transmission of sound. Yet how deplorably is it neglected! how shamefully is it misused! It can be fully developed and made what it is capable of being only through the influence of the ear. If this organ be neglected, the voice must needs be imperfect. And the voices of many persons are through life imperfect and disagreeable, because they were not carefully trained in early life to articulate distinctly, much less to utter musical sounds. The opinion is confidently expressed by those who are best qualified to decide the matter, that nearly all children might be taught to sing, if proper attention were paid early enough to the use they make of their ears and their organs of sound. The careful training of these should be considered an indispensable part of a school-teacher's as well as of a parent's duty.
The ear will find appropriate discipline in distinguishing, without aid from the eye, the causes of various sounds, as the opening of a door, the shutting of a knife, the dropping of various coins, the moving of different articles of furniture, etc. It may also find appropriate exercise in determining the direction from which various sounds proceed; in recognizing acquaintances by their natural voices, and in detecting the counterfeit voices of companions; in arranging and classifying the elementary sounds of the language, and in determining all the different musical tones; in judging of the genus and species of birds by their chirping, of the distance and nature of sonorous bodies of various kinds, etc., etc. These are some of the direct means of improving this sense: others will suggest themselves to the thoughtful reader.