95.What is the membrana tympani? Describe it.95.The circular membrane, already mentioned as closing the auditory canal, is the partition which separates the middle from the external ear, and is called themembrana tympani(c), and may be considered as the outer head of the drum of the ear. It is sometimes itself spoken of as the "drum," but this is incorrect; since a drum is not a membrane, but is the hollow space across which the membrane is stretched. This membranous drum-head is very tense and elastic, and so thin as to be almost transparent;its margin is fastened into a circular groove in the adjacent bone. Each wave of sound that impinges against this delicate membrane causes it to vibrate, and it, in turn, excites movements in the parts beyond.96.What are the ossicles? Their number and names? Their arrangement?96.Within the tympanum is arranged a chain of remarkable "little bones," orossicles. They are chiefly three in number, and from their peculiar shapes bear the following names:malleus, or the mallet;incus, or the anvil; andstapes, or the stirrup. A fourth, the smallest bone in the body, in early life intervenes between the incus and stapes, but at a later period it becomes a part of the incus. It is called theorbicularbone. Small as are these ossicles—and they, together, weigh only a few grains—they have their little muscles, cartilages, and blood-vessels, as perfectly arranged as the larger bones of the body. One end of the chain of ossicles, the mallet, is attached to the membrane of the tympanum, or outer drum-head, while the other end, the stirrup, is firmly joined by its foot-piece to a membrane in the opposite side of the cavity. The chain, accordingly, hangs suspended across the drum between the two membranes; and when the outer one vibrates under the influence of the sound-wave, the chain swings inward and transmits the vibration to the entrance of the inner ear.97.The Eustachian tube? Describe it, and state its use.97.The musical instrument, the drum, is not complete if the air within be perfectly confined: we therefore find in all instruments of this kind a small opening in the side, through which air may pass freely. By this means the pressure of the air upon the vellum which forms the head of the drum is made equal upon all sides, and the resonance of the drum remains unaffected by the varying density of the atmosphere. It will, therefore, emit its proper sound, whether it be struck in the rarified air of the mountain-top, or in the condensed air of a mine. The tympanum,or drum of the ear, in like manner has an opening by means of which it communicates freely with the external air. This opening is a narrow canal, about an inch and a half long, called theEustachian tube, after the name of its discoverer, Eustachius.Fig. 54.--Section of the Right Ear.Fig. 54.—Section of the Right Ear.A, The Concha. B, Auditory Canal. C, Membrane of the Drum, (the lower half.) D, A small muscle. E, Incus, or Anvil. M, Malleus, or Mallet. I, Eustachian Tube. G, Semicircular Canals. H, Cochlea, or snail's shell.98.What can you state of the action of the Eustachian tube?98.The course of this passage is indicated in Fig. 54,I, directed downward and inward: its other extremity opens into the upper part of the throat. The passage itself is ordinarily closed, but whenever the act of swallowing or gaping takes place, the orifice in the throat is stretched open, and the air of the cavity of the tympanum may then be renewed. Air may at will be made to enter through this tube, by closing the mouth and nose, and then tryingto force air through the latter. When this is done, a distinct crackle or clicking sound is perceived, due to the movement of the membranes, and of the little bones of the ear.99.What other purpose does the Eustachian tube serve? How is this shown? "Throat-deafness?" Primary use of the Eustachian tube?99.The Eustachian tube serves, also, as an escape-pipe for the fluids which form within the middle ear; and hence, when its lining membrane becomes thickened, in consequence of a cold, or sore throat, and the passage is thus more or less choked up, the fluids are unable to escape as usual, and therefore accumulate within the ear. When this takes place, the vibrations of the membrane are interfered with; the sounds heard appear muffled and indistinct; and a temporary difficulty of hearing, which is known as "throat-deafness," is the result. This result resembles the effect produced by interrupting the vibrations of a sonorous body, such as all are familiar with; if the finger be placed upon a piano-string or bell when it is struck, the proper sound is no longer fully and clearly emitted. But the primary use of this tube is to afford a free communication between the middle ear and the external atmosphere, and thus secure an equal pressure upon both sides of the membrane of the drum of the ear, however the density of the atmosphere may vary. If, from undue tension of the membranes, pain is experienced in the ears, when ascending into a rare atmosphere, as in a balloon, or descending into a dense one, as in a diving-bell, it may be relieved by repeating the act of swallowing, from time to time, in order that the inner and outer pressure may thus be promptly equalized.100.The essential part of the organ of hearing? Its location? Formation?100. The Internal Ear, or Labyrinth.—The most essential part of the organ of hearing is the distribution of theauditory nerve. This is found within the cavity of the internal ear, which, from its exceedingly tortuous shape,has been termed thelabyrinth(see Fig. 53,C). This cavity is hollowed out in dense bone, and consists of three parts; thevestibule(a), or ante-chamber, which is connected with the other two; thecochlea(b), or snail's shell; and the threesemicircular canals(c). The manner in which the nerve of hearing is distributed is remarkable, and is peculiar to this nerve. In the vestibule and the canals its fibres are spread out over the inner surface, not of the bony cavity but of a membranous bag, which conforms to and partially fills that cavity; and which floats in it, being both filled and surrounded with a clear, limpid fluid.101.Where is the "ear-sand" found? Give the theory as to its use.101.A singular addition to the mechanism of hearing is observed within this membranous bag of the labyrinth. This consists of two small oval ear-stones, and a quantity of fine powder of a calcareous nature, which is called "ear-sand." When examined under the microscope, these sandy particles are seen to lie scattered upon and among the delicate filaments of the auditory nerve; and it is probable, that as the tremulous sound-wave traverses the fluid of the vestibule, the sand rises and falls upon the nerve filaments, and thus intensifies the sonorous impression.102.In the cochlea or snail's shell? "Key-board" in the internal ear? The vestibules? Semicircular canals?102.In the cochlea, or snail's shell, which contains the fluid, but no membrane, the nerve ramifies upon a spiral shelf, which, like the cochlea itself, takes two and a half turns, growing continuously smaller as it winds upward. As many as three thousand nerve fibres of different lengths have been counted therein; which, it has been thought, form the grand, yet minutely small key-board, upon which strike all the musical tones that are destined to be conveyed to the brain. The vestibule, it is also supposed, takes cognizance of noise as distinguished from musical sounds; while the office of the semicircular canals is, in part at least, to prevent internal echoes, or reverberations.103.With what does the vestibule communicate? What is the theory by which sound is conducted to the brain?103.The vestibule communicates with the chain of bones of the middle ear by means of a small opening, called the "oval window," orfenestra ovalis. Across this window is stretched the membrane, which has already been alluded to as being joined to the stirrup-bone of the middle ear. Through this window, then, the sound-wave, which traverses the external and middle ear, arrives at last at the labyrinth. The limpid fluid which the latter contains, and which bathes the terminal fibres of the nerve of hearing, is thus agitated, the nerve-fibres are excited, and a sonorous impression is conducted to the brain, or, as we say, a sound is heard.104.The formation of the organ of hearing with a view to its protection?104. Protection of the Sense of Hearing.—From what has been seen of the complicated parts which compose the organ of hearing, it is evident that while many of them possess an exquisite delicacy of structure, Nature has well and amply provided for their protection. We have observed the concealed situation of the most important parts of the mechanism of the ear, the length of its cavity, its partitions, the hardness of its walls, and its communication with the atmosphere; all these provisions rendering unnecessary any supervision or care on our part in reference to the interior of the ear. But in respect to its external parts, which are under our control and within the reach of harm, it is otherwise. We may both observe the dangers which threaten them, and learn the means necessary to protect them.105.Danger to which the hearing may be subjected? Advice?105.One source of danger to the hearing consists in lowering the temperature of the ear, especially by the introduction of cold water into the auditory canal. Every one is familiar with the unpleasant sensation of distension and the confusion of sounds which accompany the filling of the ear with water when bathing: the weight of thewater within it really distends the membrane, and the cold chills the adjacent sensitive parts. It is not surprising, therefore, that the frequent introduction of cold water and its continued presence in the ear enfeeble the sense of hearing. Care should be taken to remove water from the ear after bathing, by holding the head on one side, and, at the same time, slightly expanding the outer orifice, so that the fluid may run out. For a like reason, the hair about the ears should not be allowed to remain wet, but should be thoroughly dried as soon as possible.106.The general rule as to the use of water for the ear?106.It may be stated as a general rule, to which there are but few exceptions, that no cold liquid should ever be allowed to enter the ear. When a wash or injection is rendered necessary, it should always be warmed before use. The introduction of cold air is likewise hurtful, especially when it pours through a crevice directly into the ear, as it may often do through the broken or partially closed window of a car. The avoidance of this evil gives rise to another almost as great; namely, the introduction of cotton or other soft substances into the ear to prevent it from "catching cold." This kind of protection tends to make the part unnaturally susceptible to changes of temperature, and its security seems to demand the continued presence of the "warm" covering. As a consequence of its presence, sounds are not naturally conveyed, and the sensitiveness of the nerve of hearing is gradually impaired.107.Chief source of injury to the ear? Directions for removing foreign objects from the ear? Of a live insect?107.The chief source of injury, however, to the ear is from the introduction of solid substances into the auditory canal, with the design of removing insects or other foreign objects that have found their way into the ear; or with the design of scraping out the ear-wax. For displacing a foreign object, it is usually sufficient to syringe the ear gently with warm water, the head being so held that thefluid easily escapes. If a live insect has gained entrance to the ear, it may first be suffocated by pouring a little oil upon it, and afterward removed by syringing the ear as just mentioned.108.The removal of ear-wax is generally unnecessary; for, as we have before seen, Nature provides that the excess of it shall become dry, and then spontaneously fall out in the form of fine scales. The danger from the introduction of solid implements into the outer ear is chiefly found in the fact that the membrane which lies at the bottom of it is very fragile, and that any injury of it is liable to be permanent, and to permanently impair the hearing of the injured ear.QUESTIONS FOR TOPICAL REVIEW.Give as full statements as you can on the following subjects:1. Production of sensation177,1782. Variety of sensations178,1793. General sensibility179,1804. The sensation of pain1805. The uses of pain180,181,1826. Special sensation182,1837. Organs of touch183,1848. The sense of touch184,185,1869. The delicacy of touch186,18710. Sensations of temperature and weight187,18811. The organ of taste188,18912. The sense of taste189,19013. Relations of taste, etc.190,19114. Influence of education, etc.191,19215. The sense of smell192,19316. The nerve of smell193,19417. Uses of the sense of smell194,19518. The sense of sight196,19719. Light, and the optic nerve197,19820. The organ of sight198,19921. The orbits19922. The eyelids200,20123. The lachrymal fluid201,202,20324. The eyeball203,20425. The iris205,20626. The retina206,207,208,20927. The crystalline lens209,21028. Uses of the lens210,211,21229. Long and short sight212,21330. Function of accommodation213,21431. Old sight, or presbyopia21532. Hearing and sound215,216,21733. The external ear217,218,21934. The middle ear219-22235. The internal ear222,223,22436. Protection of the sense of hearing224,225,226CHAPTER XI.The Voice.Voice and Speech—The Larynx, or the Organ of the Voice—The Vocal Cords—The Laryngoscope—The Production of the Voice—The Use of the Tongue—The different Varieties of Voice—The Change of Voice—Its Compass—Purity of Tone—Ventriloquy.1.The uttering of sounds by animals? How produced?1. Voice and Speech.—In common with the majority of the nobler animals, man possesses the power of uttering sounds, which are employed as a means of communication and expression. In man, these sounds constitute the voice; in the animals, they are designated as the cry. The song of the bird is a modification of its cry, which is rendered possible from the fact that its respiratory function is remarkably active. The sounds of the animals are generally, but not always, produced by means of their breathing organs. Among the insects, they are sometimes produced by the extremely rapid vibrations of the wings in the act of flight, as in the case of the musquito; or they are produced by the rubbing together of hard portions of the external covering of the body, as in the cricket. Almost all kinds of marine animals are voiceless. The tambour-fish and a few others have, however, the power of making a sort of noise in the water.2.The evidence of man's superior endowment? What is stated of the idiot? Parrot? Raven?2.But man alone possesses the faculty of speech, or the power to use articulate sounds in the expression of ideas, and in the communication of mind with mind. Speech is thus an evidence of the superior endowment of man, and involves the culture of the intellect. An idiot, while hemay have complete vocal organs and full power of uttering sounds or cries, is entirely incapable of speech; and, as a rule, the excellence of the language of any people will be found to be proportional to their development of brain. Man, however, is not the only being that has the power to form articulate sounds, for the parrot and the raven may also be taught to speak by rote; but man alone attaches meaning to the words and phrases he employs.3.Speech and hearing? A deaf child? Person having "no ear for music?" Impaired hearing? What do the examples show?3.Speech is intimately related to the sense of hearing. A child born deaf is, of necessity, dumb also; not because the organs of speech are imperfect, for he can utter cries and may be taught to speak, and even to converse in a rude and harsh kind of language; but because he can form no accurate notion of sound. And a person, whose hearing is not delicate, or as it is commonly expressed, who "has no ear for music," cannot sing correctly. A person who has impaired hearing commonly talks in an unnaturally loud and monotonous voice. These examples show the necessary relation of intelligence and the sense of hearing with that form of articulate voice, which is termed speech.4.Organ of the voice? Where situated? Of what is its framework composed?4. The Organ of the Voice.—The essential organ of the voice is the Larynx. This has been previously alluded to in its relation to the function of respiration; and, in the chapter on that subject, are figured the front view of that organ (Fig. 35), and its connection with the trachea, tongue, and other neighboring parts (Fig. 38). It is situated at the upper part of the neck, at the top of the trachea, or tube by which air passes into and out of the lungs. The framework of the larynx is composed of four cartilages, which render it at once very strong and sufficiently flexible to enable it to move according to the requirements of the voice.Fig. 55. Section of the Larynx and Trachea.Fig. 55. Section of the Larynx and Trachea.A, The Epiglottis. B, The Thyroid Cartilage. C, Arytenoid Cartilage. D, Ventricle of the Larynx. E, Cricoid Cartilage. F, Right Vocal Cord. H, The Trachea.5.Names, formation, and situation of the cartilages?5.The names of the cartilages are (1) thethyroid, which is a broad thin plate, bent in the middle and placed in the central line of the front part of the neck, where it is known as thepomum Adami, or Adam's apple (Fig. 55,B), and where it may be felt moving up and down with each act of swallowing; (2) thecricoid, which is shaped like a seal ring, with the broad part placed posteriorly (Fig. 55,E). At the top of the cricoid cartilage are situated the two smallarytenoidcartilages, the right one of which is shown in Fig. 55,C. These latter little organs are much more movable than the other two, and are very important in the production of the voice. They have a true ball and socket joint, and several small muscles which contract and relax with as perfect regularity and accuracy as any of the larger muscles of the body.6.Lining of the interior of the larynx? The epiglottis?6.The interior of the larynx is lined with a very sensitive mucous membrane, which is much more closely adherent to the parts beneath than is usually the case with membranes of this description. The epiglottis (A), consisting of a single leaf-shaped piece of cartilage, is attached to the front part of the larynx. It is elastic, easily moved, and fits accurately over the entrance to the air-passages below it. Its office is to guard these delicate passages and the lungs against the intrusion of food and other foreignarticles, when the act of swallowing takes place. It also assists in modifying the voice.7.Where are the vocal cords? The false cords? The true cords?7. The Vocal Cords.—Within the larynx, and stretched across it from the thyroid cartilage in front to the arytenoid cartilages behind, are placed the two sets of folds, called the vocal cords. The upper of these, one on each side, are the false cords, which are comparatively fixed and inflexible. These are not at all essential to the formation of vocal sounds, for they have been injured, in those lower animals whose larynx resembles that of man, without materially affecting their characteristic cries. Below these, one on each side, are the true vocal cords (Fig. 55,F), which pursue a similar direction to the false cords, namely, from before backward. But they are composed of a highly elastic, though strong tissue, and are covered with a thin, tightly-fitting layer of mucous membrane. Their edges are smooth and sharply defined, and when they meet, as they do in the formation of sounds, they exactly match each other.8.Where is the ventricle of the larynx? The essentials to the formation of the tones and modulation of the voice?8.Between the true and false vocal cords is a depression on each side, which is termed the ventricle of the larynx (Fig. 55,D). The integrity of these true cords, and their free vibration, are essential to the formation of the tones and the modulation of the natural voice. This is shown by the fact that, if one or both of these cords are injured or become diseased, voice and speech are compromised; or when the mucous membrane covering them becomes thickened, in consequence of a cold, the vocal sounds are rendered husky and indistinct. When an opening is made in the throat below the cords, as not infrequently happens in consequence of an attempt to commit suicide, voice is impossible except when the opening is closed by external pressure.Fig. 56. A View of the Vocal CordsFig. 56. A View of the Vocal Cords by Means of the Laryngoscope.9.Variation in the interval between the true cords of the voice? Experiment with the mirror?9.The interval or space between the true cords of the voice is constantly varying, not only when their vocal function is in exercise, but also during the act of respiration. Every time the lungs are inflated, the space increases to make wide the entrance for the air; and diminishes slightly during expiration. So that these little cords move gently to and fro in rhythm with the expansion and contraction of the chest in breathing. These movements and others may be seen to take place, if a small mirror attached to a long handle be placed back into the upper part of the throat; the handle near the mirror must be bent at an angle of 45°, so that we may look "around the corner," so to speak, behind the tongue. The position which the mirror must assume will be understood by reference to Fig. 38. A view of what may be seen under favorable circumstances, during tranquil inspiration is represented in Fig. 56. The vocal cords are there shown as narrow, white bands, on each side of the central opening, and since the image is inverted, the epiglottis appears uppermost. The rings partly seen through the opening belong to the trachea. This little mirror is the essential partof an instrument, which is called the laryngoscope, and, simple as it may seem, it is accounted one of the most valuable of the recently invented appliances of the medical art.10.The formation of true vocal tones?10. The Production of the Voice.—During ordinary tranquil breathing no sound is produced in the larynx, true vocal tones being formed only during forcible expiration, when, by an effort of the will, the cords are brought close together, and are stretched so as to be very tense. The space between them is then reduced to a narrow slit, at times not more than 1/100 of an inch in width; and the column of expired air being forced through it causes the cords to vibrate rapidly, like the strings of a musical instrument. Thus the voice is produced in its many varieties of tone and pitch; its intensity, or loudness, depending chiefly upon the power exerted in expelling the air from the lungs. When the note is high, the space is diminished both in length and width; but when it is low, the space is wider and longer (Fig. 57,B,C), and the number of vibrations is fewer within the same period of time.Fig. 57. The Different Positions of the Vocal Cords.Fig. 57. The Different Positions of the Vocal Cords.A, The position during inspiration. B, In the formation of low notes. C, In the formation of high notes.11.To what is the personal quality of the voice mainly due? What aids are there?11.The personal quality of the voice, or that which enables us to recognize a person by his speech, is mainly due to the peculiar shape of the throat, nose, and mouth, andthe resonance of the air contained within those cavities. The walls of the chest and the trachea take part in the resonance of the voice, the air within them vibrating at the same time with the parts above them. This may be tested by touching the throat or breast-bone, when a strong vocal effort is made. The teeth and the lips also are important, as is shown by the unnatural tones emitted by a person who has lost the former, or by one who is affected with the deformity known as "hare-lip." The tongue is useful, but not indispensable to speech; the case of a woman is reported, from whom nearly the whole tongue had been torn out, but who could, nevertheless, speak distinctly and even sing.12.Varieties of voice? The baritone? The voice in early youth?12. The varietiesof voice are said to be four in number; two, the bass and tenor, belonging to the male sex; and two, the contralto or alto, and soprano, peculiar to the female. The baritone voice is the name given to a variety intervening between the bass and tenor. In man, the voice is strong and grave; in woman, soft and high. In infancy and early youth, the voice is the same in both sexes, being of the soprano variety: that of boys is both clear and loud, and being susceptible of considerable training, is highly prized in the choral services of the church and cathedral. At about fourteen years of age the voice is said to change; that is, it becomes hoarse and unsteady by reason of the rapid growth of the larynx. In the case of the girl, the change is not very marked, except that the voice becomes stronger and has a wider compass; but in the boy, the larynx nearly doubles its size in a single year, the vocal cords grow thicker, longer, and coarser, and the voice becomes masculine in character. During the progress of this change, the use of the voice in singing is injudicious.13.The range of the voice? Result of careful training of the vocal organs?13.The ordinary range of each of the four varieties ofthe voice is about two octaves; but this is exceeded in the case of several celebrated vocalists. Madame Parepa-Rosa has a compass of three full octaves. When the vocal organs have been subjected to careful training, and are brought under complete control of the will, the tension of the cords become exact, and their vibrations become exceedingly precise and true. Under these circumstances the voice is said to possess "purity" of tone, and can be heard at a great distance, and above a multitude of other sounds. The power of a pure voice to make itself heard was recently exemplified in a striking manner: at a musical festival held in an audience-room of extraordinary size, and amid an orchestra of a thousand instruments and a chorus of twelve thousand voices, the artist named above also sang; yet such was the purity and strength of her voice that its notes could be clearly heard rising above the vast waves of sound produced by the full accompaniment of chorus and orchestra.14.The production of the articulate sounds? What experiment is mentioned?14.In the production of the articulate sounds of speech, the larynx is not directly concerned, but those sounds really depend upon alterations in the shape of the air-passages above that organ. That speech is not necessarily due to the action of the larynx is proven by the following simple experiment. Let an elastic tube be passed through the nostril to the back of the mouth. Then, while the breath is held, cause the tongue, teeth, and lips to go through the form of pronouncing words, and at the same time, let a second person blow through the tube into the mouth. Speech, pure and simple, or, in other words, a whisper is produced. Still further continue the experiment, while permitting vocal sounds to be made, and there will be produced a loud and whispering speech at the same moment; thus showing that voice and speech are the result of two distinct acts. Sighing, in like manner, isproduced in the mouth and throat; if, however, a vocal sound be added, the sigh is changed into a groan.15.What is ventriloquism? Indication of the original meaning of the word? How are the ventriloquous sounds produced?15. Ventriloquismis a peculiar modification of natural speech, which consists in so managing the voice that words and sounds appear to issue, not from the person, but from some distant place, as from the chimney, cellar, or the interior of a chest. The original meaning of the word ventriloquism (that is, speaking from the belly), indicates the early belief that this mode of speech was dependent upon the possession and use of some special organ besides the larynx and mouth; but at the present time, it is known that it is produced by these organs alone, and that the sources of deception consist on the part of the performer, in the dexterous management of the voice, together with a talent for mimicry; and, on the part of the auditory, in the liability of the sense of hearing to error in respect to the direction of sounds. The ventriloquist not only seems to "throw his voice," as it is said, or simulates the sound as it usually appears at a distance with but little motion of the lips and face, but he imitates the voices of an infant and of a feeble old man, of a drunken man disputing with an exasperated wife, the broken language of a foreigner, the cry of an animal in distress, demonstrating that the performer must be proficient in the art of mimicry. Ventriloquism was known to the ancient Romans and Greeks; and it is thought that the mysterious responses that were said to issue from the sacred trees and shrines of the oracles at Dodona and Delphi, were really uttered by priests who had the power of producing this form of speech.CHAPTER XII.The Use of the Microscope in the Study of Physiology.
95.What is the membrana tympani? Describe it.
95.The circular membrane, already mentioned as closing the auditory canal, is the partition which separates the middle from the external ear, and is called themembrana tympani(c), and may be considered as the outer head of the drum of the ear. It is sometimes itself spoken of as the "drum," but this is incorrect; since a drum is not a membrane, but is the hollow space across which the membrane is stretched. This membranous drum-head is very tense and elastic, and so thin as to be almost transparent;its margin is fastened into a circular groove in the adjacent bone. Each wave of sound that impinges against this delicate membrane causes it to vibrate, and it, in turn, excites movements in the parts beyond.
96.What are the ossicles? Their number and names? Their arrangement?
96.Within the tympanum is arranged a chain of remarkable "little bones," orossicles. They are chiefly three in number, and from their peculiar shapes bear the following names:malleus, or the mallet;incus, or the anvil; andstapes, or the stirrup. A fourth, the smallest bone in the body, in early life intervenes between the incus and stapes, but at a later period it becomes a part of the incus. It is called theorbicularbone. Small as are these ossicles—and they, together, weigh only a few grains—they have their little muscles, cartilages, and blood-vessels, as perfectly arranged as the larger bones of the body. One end of the chain of ossicles, the mallet, is attached to the membrane of the tympanum, or outer drum-head, while the other end, the stirrup, is firmly joined by its foot-piece to a membrane in the opposite side of the cavity. The chain, accordingly, hangs suspended across the drum between the two membranes; and when the outer one vibrates under the influence of the sound-wave, the chain swings inward and transmits the vibration to the entrance of the inner ear.
97.The Eustachian tube? Describe it, and state its use.
97.The musical instrument, the drum, is not complete if the air within be perfectly confined: we therefore find in all instruments of this kind a small opening in the side, through which air may pass freely. By this means the pressure of the air upon the vellum which forms the head of the drum is made equal upon all sides, and the resonance of the drum remains unaffected by the varying density of the atmosphere. It will, therefore, emit its proper sound, whether it be struck in the rarified air of the mountain-top, or in the condensed air of a mine. The tympanum,or drum of the ear, in like manner has an opening by means of which it communicates freely with the external air. This opening is a narrow canal, about an inch and a half long, called theEustachian tube, after the name of its discoverer, Eustachius.
Fig. 54.--Section of the Right Ear.Fig. 54.—Section of the Right Ear.A, The Concha. B, Auditory Canal. C, Membrane of the Drum, (the lower half.) D, A small muscle. E, Incus, or Anvil. M, Malleus, or Mallet. I, Eustachian Tube. G, Semicircular Canals. H, Cochlea, or snail's shell.
A, The Concha. B, Auditory Canal. C, Membrane of the Drum, (the lower half.) D, A small muscle. E, Incus, or Anvil. M, Malleus, or Mallet. I, Eustachian Tube. G, Semicircular Canals. H, Cochlea, or snail's shell.
98.What can you state of the action of the Eustachian tube?
98.The course of this passage is indicated in Fig. 54,I, directed downward and inward: its other extremity opens into the upper part of the throat. The passage itself is ordinarily closed, but whenever the act of swallowing or gaping takes place, the orifice in the throat is stretched open, and the air of the cavity of the tympanum may then be renewed. Air may at will be made to enter through this tube, by closing the mouth and nose, and then tryingto force air through the latter. When this is done, a distinct crackle or clicking sound is perceived, due to the movement of the membranes, and of the little bones of the ear.
99.What other purpose does the Eustachian tube serve? How is this shown? "Throat-deafness?" Primary use of the Eustachian tube?
99.The Eustachian tube serves, also, as an escape-pipe for the fluids which form within the middle ear; and hence, when its lining membrane becomes thickened, in consequence of a cold, or sore throat, and the passage is thus more or less choked up, the fluids are unable to escape as usual, and therefore accumulate within the ear. When this takes place, the vibrations of the membrane are interfered with; the sounds heard appear muffled and indistinct; and a temporary difficulty of hearing, which is known as "throat-deafness," is the result. This result resembles the effect produced by interrupting the vibrations of a sonorous body, such as all are familiar with; if the finger be placed upon a piano-string or bell when it is struck, the proper sound is no longer fully and clearly emitted. But the primary use of this tube is to afford a free communication between the middle ear and the external atmosphere, and thus secure an equal pressure upon both sides of the membrane of the drum of the ear, however the density of the atmosphere may vary. If, from undue tension of the membranes, pain is experienced in the ears, when ascending into a rare atmosphere, as in a balloon, or descending into a dense one, as in a diving-bell, it may be relieved by repeating the act of swallowing, from time to time, in order that the inner and outer pressure may thus be promptly equalized.
100.The essential part of the organ of hearing? Its location? Formation?
100. The Internal Ear, or Labyrinth.—The most essential part of the organ of hearing is the distribution of theauditory nerve. This is found within the cavity of the internal ear, which, from its exceedingly tortuous shape,has been termed thelabyrinth(see Fig. 53,C). This cavity is hollowed out in dense bone, and consists of three parts; thevestibule(a), or ante-chamber, which is connected with the other two; thecochlea(b), or snail's shell; and the threesemicircular canals(c). The manner in which the nerve of hearing is distributed is remarkable, and is peculiar to this nerve. In the vestibule and the canals its fibres are spread out over the inner surface, not of the bony cavity but of a membranous bag, which conforms to and partially fills that cavity; and which floats in it, being both filled and surrounded with a clear, limpid fluid.
101.Where is the "ear-sand" found? Give the theory as to its use.
101.A singular addition to the mechanism of hearing is observed within this membranous bag of the labyrinth. This consists of two small oval ear-stones, and a quantity of fine powder of a calcareous nature, which is called "ear-sand." When examined under the microscope, these sandy particles are seen to lie scattered upon and among the delicate filaments of the auditory nerve; and it is probable, that as the tremulous sound-wave traverses the fluid of the vestibule, the sand rises and falls upon the nerve filaments, and thus intensifies the sonorous impression.
102.In the cochlea or snail's shell? "Key-board" in the internal ear? The vestibules? Semicircular canals?
102.In the cochlea, or snail's shell, which contains the fluid, but no membrane, the nerve ramifies upon a spiral shelf, which, like the cochlea itself, takes two and a half turns, growing continuously smaller as it winds upward. As many as three thousand nerve fibres of different lengths have been counted therein; which, it has been thought, form the grand, yet minutely small key-board, upon which strike all the musical tones that are destined to be conveyed to the brain. The vestibule, it is also supposed, takes cognizance of noise as distinguished from musical sounds; while the office of the semicircular canals is, in part at least, to prevent internal echoes, or reverberations.
103.With what does the vestibule communicate? What is the theory by which sound is conducted to the brain?
103.The vestibule communicates with the chain of bones of the middle ear by means of a small opening, called the "oval window," orfenestra ovalis. Across this window is stretched the membrane, which has already been alluded to as being joined to the stirrup-bone of the middle ear. Through this window, then, the sound-wave, which traverses the external and middle ear, arrives at last at the labyrinth. The limpid fluid which the latter contains, and which bathes the terminal fibres of the nerve of hearing, is thus agitated, the nerve-fibres are excited, and a sonorous impression is conducted to the brain, or, as we say, a sound is heard.
104.The formation of the organ of hearing with a view to its protection?
104. Protection of the Sense of Hearing.—From what has been seen of the complicated parts which compose the organ of hearing, it is evident that while many of them possess an exquisite delicacy of structure, Nature has well and amply provided for their protection. We have observed the concealed situation of the most important parts of the mechanism of the ear, the length of its cavity, its partitions, the hardness of its walls, and its communication with the atmosphere; all these provisions rendering unnecessary any supervision or care on our part in reference to the interior of the ear. But in respect to its external parts, which are under our control and within the reach of harm, it is otherwise. We may both observe the dangers which threaten them, and learn the means necessary to protect them.
105.Danger to which the hearing may be subjected? Advice?
105.One source of danger to the hearing consists in lowering the temperature of the ear, especially by the introduction of cold water into the auditory canal. Every one is familiar with the unpleasant sensation of distension and the confusion of sounds which accompany the filling of the ear with water when bathing: the weight of thewater within it really distends the membrane, and the cold chills the adjacent sensitive parts. It is not surprising, therefore, that the frequent introduction of cold water and its continued presence in the ear enfeeble the sense of hearing. Care should be taken to remove water from the ear after bathing, by holding the head on one side, and, at the same time, slightly expanding the outer orifice, so that the fluid may run out. For a like reason, the hair about the ears should not be allowed to remain wet, but should be thoroughly dried as soon as possible.
106.The general rule as to the use of water for the ear?
106.It may be stated as a general rule, to which there are but few exceptions, that no cold liquid should ever be allowed to enter the ear. When a wash or injection is rendered necessary, it should always be warmed before use. The introduction of cold air is likewise hurtful, especially when it pours through a crevice directly into the ear, as it may often do through the broken or partially closed window of a car. The avoidance of this evil gives rise to another almost as great; namely, the introduction of cotton or other soft substances into the ear to prevent it from "catching cold." This kind of protection tends to make the part unnaturally susceptible to changes of temperature, and its security seems to demand the continued presence of the "warm" covering. As a consequence of its presence, sounds are not naturally conveyed, and the sensitiveness of the nerve of hearing is gradually impaired.
107.Chief source of injury to the ear? Directions for removing foreign objects from the ear? Of a live insect?
107.The chief source of injury, however, to the ear is from the introduction of solid substances into the auditory canal, with the design of removing insects or other foreign objects that have found their way into the ear; or with the design of scraping out the ear-wax. For displacing a foreign object, it is usually sufficient to syringe the ear gently with warm water, the head being so held that thefluid easily escapes. If a live insect has gained entrance to the ear, it may first be suffocated by pouring a little oil upon it, and afterward removed by syringing the ear as just mentioned.
108.The removal of ear-wax is generally unnecessary; for, as we have before seen, Nature provides that the excess of it shall become dry, and then spontaneously fall out in the form of fine scales. The danger from the introduction of solid implements into the outer ear is chiefly found in the fact that the membrane which lies at the bottom of it is very fragile, and that any injury of it is liable to be permanent, and to permanently impair the hearing of the injured ear.
QUESTIONS FOR TOPICAL REVIEW.
Give as full statements as you can on the following subjects:
CHAPTER XI.
Voice and Speech—The Larynx, or the Organ of the Voice—The Vocal Cords—The Laryngoscope—The Production of the Voice—The Use of the Tongue—The different Varieties of Voice—The Change of Voice—Its Compass—Purity of Tone—Ventriloquy.
Voice and Speech—The Larynx, or the Organ of the Voice—The Vocal Cords—The Laryngoscope—The Production of the Voice—The Use of the Tongue—The different Varieties of Voice—The Change of Voice—Its Compass—Purity of Tone—Ventriloquy.
1.The uttering of sounds by animals? How produced?
1. Voice and Speech.—In common with the majority of the nobler animals, man possesses the power of uttering sounds, which are employed as a means of communication and expression. In man, these sounds constitute the voice; in the animals, they are designated as the cry. The song of the bird is a modification of its cry, which is rendered possible from the fact that its respiratory function is remarkably active. The sounds of the animals are generally, but not always, produced by means of their breathing organs. Among the insects, they are sometimes produced by the extremely rapid vibrations of the wings in the act of flight, as in the case of the musquito; or they are produced by the rubbing together of hard portions of the external covering of the body, as in the cricket. Almost all kinds of marine animals are voiceless. The tambour-fish and a few others have, however, the power of making a sort of noise in the water.
2.The evidence of man's superior endowment? What is stated of the idiot? Parrot? Raven?
2.But man alone possesses the faculty of speech, or the power to use articulate sounds in the expression of ideas, and in the communication of mind with mind. Speech is thus an evidence of the superior endowment of man, and involves the culture of the intellect. An idiot, while hemay have complete vocal organs and full power of uttering sounds or cries, is entirely incapable of speech; and, as a rule, the excellence of the language of any people will be found to be proportional to their development of brain. Man, however, is not the only being that has the power to form articulate sounds, for the parrot and the raven may also be taught to speak by rote; but man alone attaches meaning to the words and phrases he employs.
3.Speech and hearing? A deaf child? Person having "no ear for music?" Impaired hearing? What do the examples show?
3.Speech is intimately related to the sense of hearing. A child born deaf is, of necessity, dumb also; not because the organs of speech are imperfect, for he can utter cries and may be taught to speak, and even to converse in a rude and harsh kind of language; but because he can form no accurate notion of sound. And a person, whose hearing is not delicate, or as it is commonly expressed, who "has no ear for music," cannot sing correctly. A person who has impaired hearing commonly talks in an unnaturally loud and monotonous voice. These examples show the necessary relation of intelligence and the sense of hearing with that form of articulate voice, which is termed speech.
4.Organ of the voice? Where situated? Of what is its framework composed?
4. The Organ of the Voice.—The essential organ of the voice is the Larynx. This has been previously alluded to in its relation to the function of respiration; and, in the chapter on that subject, are figured the front view of that organ (Fig. 35), and its connection with the trachea, tongue, and other neighboring parts (Fig. 38). It is situated at the upper part of the neck, at the top of the trachea, or tube by which air passes into and out of the lungs. The framework of the larynx is composed of four cartilages, which render it at once very strong and sufficiently flexible to enable it to move according to the requirements of the voice.
Fig. 55. Section of the Larynx and Trachea.Fig. 55. Section of the Larynx and Trachea.A, The Epiglottis. B, The Thyroid Cartilage. C, Arytenoid Cartilage. D, Ventricle of the Larynx. E, Cricoid Cartilage. F, Right Vocal Cord. H, The Trachea.
A, The Epiglottis. B, The Thyroid Cartilage. C, Arytenoid Cartilage. D, Ventricle of the Larynx. E, Cricoid Cartilage. F, Right Vocal Cord. H, The Trachea.
5.Names, formation, and situation of the cartilages?
5.The names of the cartilages are (1) thethyroid, which is a broad thin plate, bent in the middle and placed in the central line of the front part of the neck, where it is known as thepomum Adami, or Adam's apple (Fig. 55,B), and where it may be felt moving up and down with each act of swallowing; (2) thecricoid, which is shaped like a seal ring, with the broad part placed posteriorly (Fig. 55,E). At the top of the cricoid cartilage are situated the two smallarytenoidcartilages, the right one of which is shown in Fig. 55,C. These latter little organs are much more movable than the other two, and are very important in the production of the voice. They have a true ball and socket joint, and several small muscles which contract and relax with as perfect regularity and accuracy as any of the larger muscles of the body.
6.Lining of the interior of the larynx? The epiglottis?
6.The interior of the larynx is lined with a very sensitive mucous membrane, which is much more closely adherent to the parts beneath than is usually the case with membranes of this description. The epiglottis (A), consisting of a single leaf-shaped piece of cartilage, is attached to the front part of the larynx. It is elastic, easily moved, and fits accurately over the entrance to the air-passages below it. Its office is to guard these delicate passages and the lungs against the intrusion of food and other foreignarticles, when the act of swallowing takes place. It also assists in modifying the voice.
7.Where are the vocal cords? The false cords? The true cords?
7. The Vocal Cords.—Within the larynx, and stretched across it from the thyroid cartilage in front to the arytenoid cartilages behind, are placed the two sets of folds, called the vocal cords. The upper of these, one on each side, are the false cords, which are comparatively fixed and inflexible. These are not at all essential to the formation of vocal sounds, for they have been injured, in those lower animals whose larynx resembles that of man, without materially affecting their characteristic cries. Below these, one on each side, are the true vocal cords (Fig. 55,F), which pursue a similar direction to the false cords, namely, from before backward. But they are composed of a highly elastic, though strong tissue, and are covered with a thin, tightly-fitting layer of mucous membrane. Their edges are smooth and sharply defined, and when they meet, as they do in the formation of sounds, they exactly match each other.
8.Where is the ventricle of the larynx? The essentials to the formation of the tones and modulation of the voice?
8.Between the true and false vocal cords is a depression on each side, which is termed the ventricle of the larynx (Fig. 55,D). The integrity of these true cords, and their free vibration, are essential to the formation of the tones and the modulation of the natural voice. This is shown by the fact that, if one or both of these cords are injured or become diseased, voice and speech are compromised; or when the mucous membrane covering them becomes thickened, in consequence of a cold, the vocal sounds are rendered husky and indistinct. When an opening is made in the throat below the cords, as not infrequently happens in consequence of an attempt to commit suicide, voice is impossible except when the opening is closed by external pressure.
Fig. 56. A View of the Vocal CordsFig. 56. A View of the Vocal Cords by Means of the Laryngoscope.
9.Variation in the interval between the true cords of the voice? Experiment with the mirror?
9.The interval or space between the true cords of the voice is constantly varying, not only when their vocal function is in exercise, but also during the act of respiration. Every time the lungs are inflated, the space increases to make wide the entrance for the air; and diminishes slightly during expiration. So that these little cords move gently to and fro in rhythm with the expansion and contraction of the chest in breathing. These movements and others may be seen to take place, if a small mirror attached to a long handle be placed back into the upper part of the throat; the handle near the mirror must be bent at an angle of 45°, so that we may look "around the corner," so to speak, behind the tongue. The position which the mirror must assume will be understood by reference to Fig. 38. A view of what may be seen under favorable circumstances, during tranquil inspiration is represented in Fig. 56. The vocal cords are there shown as narrow, white bands, on each side of the central opening, and since the image is inverted, the epiglottis appears uppermost. The rings partly seen through the opening belong to the trachea. This little mirror is the essential partof an instrument, which is called the laryngoscope, and, simple as it may seem, it is accounted one of the most valuable of the recently invented appliances of the medical art.
10.The formation of true vocal tones?
10. The Production of the Voice.—During ordinary tranquil breathing no sound is produced in the larynx, true vocal tones being formed only during forcible expiration, when, by an effort of the will, the cords are brought close together, and are stretched so as to be very tense. The space between them is then reduced to a narrow slit, at times not more than 1/100 of an inch in width; and the column of expired air being forced through it causes the cords to vibrate rapidly, like the strings of a musical instrument. Thus the voice is produced in its many varieties of tone and pitch; its intensity, or loudness, depending chiefly upon the power exerted in expelling the air from the lungs. When the note is high, the space is diminished both in length and width; but when it is low, the space is wider and longer (Fig. 57,B,C), and the number of vibrations is fewer within the same period of time.
Fig. 57. The Different Positions of the Vocal Cords.Fig. 57. The Different Positions of the Vocal Cords.A, The position during inspiration. B, In the formation of low notes. C, In the formation of high notes.
A, The position during inspiration. B, In the formation of low notes. C, In the formation of high notes.
11.To what is the personal quality of the voice mainly due? What aids are there?
11.The personal quality of the voice, or that which enables us to recognize a person by his speech, is mainly due to the peculiar shape of the throat, nose, and mouth, andthe resonance of the air contained within those cavities. The walls of the chest and the trachea take part in the resonance of the voice, the air within them vibrating at the same time with the parts above them. This may be tested by touching the throat or breast-bone, when a strong vocal effort is made. The teeth and the lips also are important, as is shown by the unnatural tones emitted by a person who has lost the former, or by one who is affected with the deformity known as "hare-lip." The tongue is useful, but not indispensable to speech; the case of a woman is reported, from whom nearly the whole tongue had been torn out, but who could, nevertheless, speak distinctly and even sing.
12.Varieties of voice? The baritone? The voice in early youth?
12. The varietiesof voice are said to be four in number; two, the bass and tenor, belonging to the male sex; and two, the contralto or alto, and soprano, peculiar to the female. The baritone voice is the name given to a variety intervening between the bass and tenor. In man, the voice is strong and grave; in woman, soft and high. In infancy and early youth, the voice is the same in both sexes, being of the soprano variety: that of boys is both clear and loud, and being susceptible of considerable training, is highly prized in the choral services of the church and cathedral. At about fourteen years of age the voice is said to change; that is, it becomes hoarse and unsteady by reason of the rapid growth of the larynx. In the case of the girl, the change is not very marked, except that the voice becomes stronger and has a wider compass; but in the boy, the larynx nearly doubles its size in a single year, the vocal cords grow thicker, longer, and coarser, and the voice becomes masculine in character. During the progress of this change, the use of the voice in singing is injudicious.
13.The range of the voice? Result of careful training of the vocal organs?
13.The ordinary range of each of the four varieties ofthe voice is about two octaves; but this is exceeded in the case of several celebrated vocalists. Madame Parepa-Rosa has a compass of three full octaves. When the vocal organs have been subjected to careful training, and are brought under complete control of the will, the tension of the cords become exact, and their vibrations become exceedingly precise and true. Under these circumstances the voice is said to possess "purity" of tone, and can be heard at a great distance, and above a multitude of other sounds. The power of a pure voice to make itself heard was recently exemplified in a striking manner: at a musical festival held in an audience-room of extraordinary size, and amid an orchestra of a thousand instruments and a chorus of twelve thousand voices, the artist named above also sang; yet such was the purity and strength of her voice that its notes could be clearly heard rising above the vast waves of sound produced by the full accompaniment of chorus and orchestra.
14.The production of the articulate sounds? What experiment is mentioned?
14.In the production of the articulate sounds of speech, the larynx is not directly concerned, but those sounds really depend upon alterations in the shape of the air-passages above that organ. That speech is not necessarily due to the action of the larynx is proven by the following simple experiment. Let an elastic tube be passed through the nostril to the back of the mouth. Then, while the breath is held, cause the tongue, teeth, and lips to go through the form of pronouncing words, and at the same time, let a second person blow through the tube into the mouth. Speech, pure and simple, or, in other words, a whisper is produced. Still further continue the experiment, while permitting vocal sounds to be made, and there will be produced a loud and whispering speech at the same moment; thus showing that voice and speech are the result of two distinct acts. Sighing, in like manner, isproduced in the mouth and throat; if, however, a vocal sound be added, the sigh is changed into a groan.
15.What is ventriloquism? Indication of the original meaning of the word? How are the ventriloquous sounds produced?
15. Ventriloquismis a peculiar modification of natural speech, which consists in so managing the voice that words and sounds appear to issue, not from the person, but from some distant place, as from the chimney, cellar, or the interior of a chest. The original meaning of the word ventriloquism (that is, speaking from the belly), indicates the early belief that this mode of speech was dependent upon the possession and use of some special organ besides the larynx and mouth; but at the present time, it is known that it is produced by these organs alone, and that the sources of deception consist on the part of the performer, in the dexterous management of the voice, together with a talent for mimicry; and, on the part of the auditory, in the liability of the sense of hearing to error in respect to the direction of sounds. The ventriloquist not only seems to "throw his voice," as it is said, or simulates the sound as it usually appears at a distance with but little motion of the lips and face, but he imitates the voices of an infant and of a feeble old man, of a drunken man disputing with an exasperated wife, the broken language of a foreigner, the cry of an animal in distress, demonstrating that the performer must be proficient in the art of mimicry. Ventriloquism was known to the ancient Romans and Greeks; and it is thought that the mysterious responses that were said to issue from the sacred trees and shrines of the oracles at Dodona and Delphi, were really uttered by priests who had the power of producing this form of speech.
CHAPTER XII.