CHAPTER XXIX.

THE CONSTRUCTION AND CARE OF THE EAR.

HE human ear is not to be regarded as of the best possible

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form, nor as always in the best position for the collection of sounds. One will observe in the lower animals, in many of which the hearing is far more acute than in man, that the ear is larger, of simpler form, and mobile. Among some of these the concavity of the ear can be directed toward the place whence the sound seems to proceed. Doubtless the human ear was originally of a very different shape from its present one, and the convolutions which it now possesses represent a general collapse of the organ, the absence of its motile power having coincidently come about in the course of ages, as being no longer needful in man's present higher stage of existence. Darwin even thought that the point on the inner side of the selvedge-edge of the ear, about a third of the way from the top, which is a very marked feature of the organ in some few individuals, is to be recognized as the rudiment of a former peak of the ear. He also enlarges upon the fact, known to some persons, that in certain individuals the ear can be moved at will. Darwin's idea of the rudiment of which we speak being the representative of a former tip of the ear, now folded in, brings with it a vivid reminiscence of Hawthorne's Donatello, in the "Marble Faun," that strange creature who touched so nearly on primeval nature.

If any one should think it superfluous to mention that the ear is not, as compared with that of some of the lower animals, well adapted to collecting sounds, it will be sufficient to say to such a one, that the fact is not always apparent. Even so learned a man man as Reis, a German professor, who, in 1860, undoubtedly invented the telephone, evidently had so much (353)

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confidence in the shape of the human ear as the fittest vehicle for at least the sound of speech, that he constructed his first telephone with a receiver (called in telephony "the transmitter") shaped like the human ear. The ear receives any sounds fairly well, although how much better it would receive them if it presented a larger concave surface, capable of moving, is proved by the common practice of one hard of hearing, in adjusting the curved hand back of the ear with reference both to the intensity and direction of the sound sought to be heard.

The human ear in the present human life is not, be it understood, ill-adapted to the requirement of it. It is the requirement of it which has largely contributed to stamp it as what it is. We are but comparing it with ears of finer organization for hearing. Its existing convolutions are serviceable in directing sounds through the passage upon the drum of the ear, as has been tested by filling up the convolutions with some plastic material, like wax, whereupon the diminution in hearing became appreciable. But surely, as we have proved by citing a single experiment, which any one can try for himself, we should hear better if the ear were larger and differently shaped and capable of movement. This fact, however, does not involve the conclusion that we should be equal even then in acuteness of hearing to some of the lower animals, the interior apparatus of whose ears is evidently more highly organized than ours. As mankind have advanced in intellectual power, and have developed the inventive faculty, they have become less and less dependent upon the strength and the acuteness of their merely physical attributes. They must have been untold centuries without an acute sense of hearing, even as it is found where most highly developed in human beings, among savages. Yet it is only very recently that, in the German army, dogs have been trained in connection with outpost duty, a service in which their special keenness of hearing admirably supplements the intelligence

of videttes. It is truly remarkable that this use of the dog had never previously been made a part of regular military administration.

The outer ear collects waves of sound and transmits them through a short channel terminated by a tense membrane having the same function as that of the parchment head of a drum. This membrane is, for that reason, called the drum-membrane of the ear. The drum of the ear is constituted by that membrane and the chamber which it closes. Delicately attached to the back of this membrane is the end of a small bone, called the hammer. The hammer, at its other end, is jointed with another bone, called the anvil. The anvil, in turn, is jointed with a third small bone, called the stirrup. These three articulated bones together form what is known as a compound lever.

When a sound from the outer world strikes upon the drummembrane of the ear, it makes that membrane vibrate with the intensity and quality of the impulse which characterize the sound. This vibration is taken up by the end of the lever forming the hammer, conveyed thence to the anvil, and thence to the stirrup.

At the stirrup a new series of physical characters present themselves, completed by the phenomenon of hearing. The bottom of the stirrup is in contact with an oval opening into the solid temporal bone, which opening, likened to a window, is covered by a membrane. Beyond this oval, membrane-covered window, and carved out, as it were, in the dense bone, is what is called the labyrinth,—a chamber consisting of beautifully curved passages, in which is a membranous sac containing and surrounded by fluid. The finer details of the structure of the labyrinth are too numerous and complicated to be here described, relating, as they do, to the minutest anatomical research assisted by the microscope. Suffice it to say that, immeshed in this membranous sac, filling the bony passages of the labyrinth, spread

out the hair-like terminal filaments of the auditory nerve, by means of which the perception of sound becomes one of the functions of the brain.

Here, at the labyrinth, the new departure, after the vibration from the drum-membrane has reached the oval, membranecovered window of the labyrinth, begins and ends with the sensation of hearing. The bottom of the stirrup conveys the vibration to the oval, membrane-covered window; that membrane transmits the impulse, in quantity and quality, to the fluid inside of the membranous sac in the labyrinth; it, in turn, transmits the impulse to the long, hair-like processes that lie spread out within the sac; and, lastly, they transmit it to the auditory nerve, whence, as a finality, it reaches the brain. Here, however, as in the case of the eye and the faculty of seeing, we reach a point incapable of solution by the human intellect. How is it that a vibration-a transient physical fact, communicated to the auditory nerve-ceases to have merely physical attributes, and is translated from a sensation into an emotion? It is impossible that any one should ever be able to find out the reason for this. If any one think so, he is ignorant, or presumptuous beyond the bounds of expression to characterize his folly.

It must seem to the general reader as if all that is necessary to a description of the ear had been said, and yet, were there not something else added, the structure would have been described as very imperfect. It is requisite to the excellence of the apparatus of the ear that there should be a constant supply of air in the drum-chamber. The special apparatus which supplies this need is called the Eustachian tube,-a tube from 1 to 2 inches long, situated at the side and rear of the upper part of the throat, opening from the portion of the throat that is called the pharynx. During swallowing this passage closes. Air is, however, at the normal tension, supplied through this passage to the drum-chamber, thus equalizing the atmospheric

pressure on the opposite sides of the drum-membrane. If it were not for this, the atmospheric pressure on the outside would force the drum-membrane constantly inward; a certain muscle connected with it would not be able to act efficiently upon it, and, besides, sound could not be conveyed so readily, as now across the drum-chamber.

When the opening of the Eustachian tube into the pharynx is partially closed by inflammation of the throat, as from cold, or from some other cause, the hearing is much impaired. We can, upon reflection, realize that this must occur when we know that, although the chief agent in conveying the vibration of sound across from the drum-membrane to the oval, membranous window of the labyrinth is the compound lever formed of the hammer, anvil, and stirrup, yet that air in the drum-chamber must also be a medium for the conveyance of the vibration. For this reason persons hard of hearing hear so much better when they use one of the modern flexible fans constructed for deafness, which is bowed at pleasure with a string, and the upper edge of it placed between the teeth. We hear by the affection mediately of dif ferent surrounding parts of the auditory apparatus. Primarily, we hear by means of the action of the base of the stirrup on the oval window, and by means of vibration of the air in the drumchamber acting on the oval window; but if any one has ever been in bathing, as we have, during a severe thunder-storm, he knows from the intensity of the sound, if he has happened to plunge his head under water during a violent peal of thunder, that vibrations are communicated directly to the ear from every portion of the bony structure of the cranium, as well as through the passage of the outer ear, and, perhaps, despite the closed lips and teeth, through the Eustachian tube. At any rate, the din is frightful, and of singular complexity of sound effect.

In cerebral disease, impressions of hearing may be due to physical causes not proceeding from the outer world. The