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EXPERIMENTS ON DEAD LARYNX.

axis of the vocal tube, become perpendicular to it, and as the edges of the glottis approximate, its chink is nearly or entirely closed, and they acquire the true vibrating position. The production of the most simple tones of the voice requires the associated action of a most extensive range of organs; for it is calculated that in the ordinary modulation of the voice, more than one hundred muscles are brought into action at the same time.

As the air rushes upwards from the windpipe, a portion of each edge of the glottis yields to its pressure, and is curved upwards, so as to form an angle with the axis of the vocal tube, and leave between the two edges a narrow aperture, through which the air escapes. The tension and elasticity of the vocal ligaments tend to restore them to the plane of their former position. The air having been rarefied below the glottis during their elevation, becomes dense from their depression, and the necessary force being again accumulated, they are re-elevated, and thus an oscillating movement, consisting of an opening and closing of the glottis, takes place, which being communicated to the contiguous air, the sounds of the voice are produced.

The vibrating edge of the glottis varies in length according to the pressure of the column of air in the windpipe, and the resistance of the vocal ligaments. When other circumstances are alike, the intensity of the voice is determined by the pressure of the column of air in the windpipe, and the range of movement described by the vibrating edges of the glottis. The pitch of the voice does not depend solely on the tension of the vocal ligaments, but jointly on the variations which they undergo in length and tension. Magendie observed, in the larynx of a dog, that a longer portion of the vocal

ligaments vibrated while grave tones were produced, and that a diminution of length accompanied the succession of acute tones. Mayo has described the movements of the glottis in a man who had attempted to destroy himself by cutting his throat. The larynx in this case was cut through just above the vocal cords, and, owing to the oblique direction of the wound, an injury of the arytenoid cartilage and of the vocal cord on one side had occurred. When respiration was going on, the glottis was seen to be of a triangular form, but when the voice was exerted, the vocal cords passed into a parallel direction, and the glottis itself had a linear form. The posterior part of the aperture appeared to remain unclosed.

The cut represents the prepared head of a corpse, after Müller. A thread e, which passes over a roller to a scale, is so applied to the larynx that the tension of the vocal cords can be increased by placing a greater weight on the scale. The action of the muscles is thereby imitated. The compressing apparatus seen on the wood-cut brings the vocal cords nearer to

each other, and thus produces the requisite diminution in the width of the vocal fissure. The tube ƒ serves to convey the wind, which throws the tongue-apparatus into action.

OBJECTIONS TO THE TRUE THEORY OF VOICE.

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And thus, if we use the human head, or the head of the dog, or of the pig, or of any other animal, we can imitate the voice of man, the bark of the dog, the grunt of the pig, &c.

Membranous tongues, like those in the larynx, differ widely from a metal tongue, shutting up the aperture, and necessarily opening and closing as the air issues.

Objections have been taken to the view which represents the voice as the result of sounds produced by membranous tongues set in motion by air, 1st, That the vibration of tongues consists in the periodical opening and shutting of the orifice through which the stream of air passes, this not being the case in the glottis; 2nd, That had it the structure of a reed, the edges of the vocal ligaments which open the chink would be alternately separated by the column of air in the larynx, and drawn together by their tension, while it has been found by experiment that air transmitted through the glottis gives rise to sound, notwithstanding that its edges are from one-sixth to one-fourth of an inch asunder In these objections, however, there is a mistake as to the essential principel of reeds-for those of the clarionet, bassoon, hautboy, &c., fail to close entirely the passages through which the breath escapes; and the case is not otherwise with the natural reed, which the lips of players on the flute and horn represent. In short, a sound can be produced by a tongue apart from the surrounding framework, indicating, beyond doubt, that so much importance should not be ascribed to the usual mode of forming reeded and tongued instruments, and to the circumstance of the air passing between the tongue and its frame. It has been shown that the law by which the variation in the notes yielded by the tongue of a mouthpiece or reed is regulated, is the same when the tongue is made to vibrate by a current of air, as when it is thrown into vibrations by being struck or inflected. By the same law are regulated the vibrations of vibrating rods; the frequency of the vibrations of two rods of the same texture and thickness being in the inverse ratio of the squares of their length. The note afforded by a reed without a tube is of the same pitch, whether it be the result of a current of air, or be produced by striking the tongue. The strength of the blast does not, for the most part, determine the pitch or sharpness of the note; but when the force of the blowing is increased, the strength of the tones is augmented. The size of the fissure between the tongue and the frame within which it vibrates, is of little consequence; when the opening is large there is a greater difficulty in obtaining the tone, but its pitch is not altered.

Some slight difficulties may still exist in the explanation of the theory of the voice as considered to be chiefly the result of a double vibrating tongue; but, altogether, as close a resemblance has been proved to exist between that kind of artificial musical arrangement and the structure of the living larynx, as can reasonably be expected in such a case.

It was already hinted that the vocal ligaments may possibly act not only as vibrating tongues in the production of voice, but also on the principle of musical strings. On this point a few words must be added. It may seem at first sight that the remark of so distinguished a philosopher as Biot, when he says, "What is there in the larynx that resembles a vibrating string? Where is the space for such a string of sufficient length to yield the lower notes of the voice? How could sounds, of the compass which the human voice represents, be produced by a string which the larynx would contain ?" would suffice altogether to set aside the idea of the vocal cords acting as musical strings. But Biot here seems to have fallen into error. Deep notes are still produced by a string greatly shortened, if it retain, after a sufficient amount of relaxation, the elasticity

ORGANIC NATURE.-No. V.

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ANIMAL MEMBRANES PRODUCE SOUND

required for vibration. His attention does not seem to have been drawn sufficiently to the nature of organic membranes, strips of India rubber and elastic animal membranes still retaining enough of elasticity for this purpose, after being much relaxed. There is, therefore, a perfect agreement between the vocal cords and vibrating strings, though their vibrations, whether as strings or as tongues, are produced not by the direct impulse of a solid body, but by the momentum of air. When the ordinary principles to which musical strings are subject are applied to the vocal ligaments, there is found to be a very close agreement, if allowance is made for the peculiarities of elastic animal substances as respects elasticity and the like.

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In their ordinary state, the vocal cords must be regarded as subject to a considerable tension, which, however, admits of being diminished, so as to add to the range of the lower notes. At the ordinary pitch of the voice, the glottis may be regarded as partially closed, and becoming more open as graver tones are produced; this opening of the glottis coinciding with the relaxation of the vocal cords, a double cause is afforded of the lowering of tone. When higher notes are uttered the glottis closes, assuming more of a linear form, while, at the same time, the vocal ligaments, though elongated, are thrown into a much higher state of tension. In the words, then, of Mr. Bishop, "since the vocal ligaments have been proved to extend and contract for acute and grave sounds respectively, and after death vibrate in a great measure like musical strings, we think it may be fairly inferred that they likewise obey, to a certain extent, during life, the laws of the vibrations of such strings." "It is moreover observable, that the extension and relaxation of the vocal cord, which, as we have seen, are analogous to those of a musical string, produce a corresponding shortening and elongation of its axis, regarded as a tongue; and, lastly, since one tone only is produced at a time, the vibrations resulting from the double action which appears to exist in the vocal apparatus must be synchronous." * * * "It might possibly be objected to the idea of this two-fold action, that the production of sound by the vocal cords is sufficiently accounted for by supposing them to vibrate merely as elastic tongues; but then it is found by experiment, that by artificially dividing their length into two ventral segments, there results the octave of the fundamental note, which proves that at all events they vibrate as cords. In conclusion, we must bear in mind the vast difference between natural and artificial mechanism, and however complicated a problem it may be to determine that constitution of the vocal apparatus, by which the thyro-arytenoid ligaments may simultaneously obey the laws of cords and tongues, yet to a physiologist who is accustomed to meet with the most admirable contrivances and combinations in the animal frame, the difficulty of finding a strictly mathematical solution is, in such a case, no objection to its truth, when the facts, as far as they have been observed, are decidedly favourable to its reality."-Cyclopædia of Physiology, article Voice, p. 1481.

It was before hinted at, that the vibrations of the walls of the tubes through which the voice is conducted may, in some degree, influence its sound. In rigid tubes, the vibrations depend on the nature of the impulse propagated in the air within, jointly with the length of the pipe. So long, then, as the length of the pipe remains the same, and no change takes place on the material of its walls, the pitch of the sound produced by the undulations of the air within, remains unaffected. The dimensions of the windpipe, such as its length and diameter, are invariable; and, were the height of the larynx, and the dimensions of the bifid tube (the nose and mouth) through which the air issues after the formation of voice, equally invariable, the vibrations of these parts

would produce no change on the pitch of the voice, the quantities being constant for each tone produced in the glottis. It has been found that, by taking tubes composed of layers of paper, of constant length, but varied in thickness, graver sounds were produced as the parietes became thinner, and that the gravity of the sound was increased by moistening and relaxing the sides of the tubes. It was before noticed, that the windpipe is capable of being drawn upwards from the chest to a small extent, while the larynx is elevated, and that this tube admits of being diminished in its diameter by about one-third part. Moreover, the pharynx, the mouth, and the nasal cavities are also susceptible of various modifications of diameter, so that the pipe, so to speak, near the middle of which the vocal sound is produced, is in a very different condition from a rigid tube. Hence, it has been concluded that provision is made for an invariable adaptation between the amount of tension, the vibrating length of the vocal ligaments, and the walls of the vocal tube, for the production of the ordinary tones of the voice. It appears, indeed, to have been proved that the vocal tube is so short, that were it rigid, it could not influence the pitch of the note which the glottis originates. But its want of length is compensated for by the relaxation of its walls, so that it comes to vibrate synchronously, and so to give forth sounds equally grave with those of the glottis. Its effect, therefore, is to add to the force of the tone, which, without its aid, would have been found to possess less intensity.

After considering this subject in every possible light, the conclusion appears to be that to which Mr. Bishop has come, namely, that the evidence shows "the vocal apparatus to be influenced by the air expelled from the chest, in precisely the same way as if it were a stretched cord, a reed, or a vibrating tube. Why, then," he continues, "should we hesitate to adopt the obvious conclusion that the vocal organs do, in fact, combine the properties of these various instruments, and are thus the perfect types of which these instruments are only imperfect imitations ?"

Singing.-The notes of the human voice are capable of being produced in three separate kinds of sequence. In ordinary speaking, the successive notes have nearly all the same pitch. This kind of succession, then, is properly termed the monotonous. Some deviation from this monotony occasionally arises, as when certain syllables receive a higher intonation for the sake of accent, and when, in reading or reciting poetry, rhythm is added to the accent. In these cases, however, the deviation from monotony of pitch is too slight to require a separate head. In the expression of passion, accompanied by vehement exercise of the voice, there is heard a sudden transition from high to low notes, or the reverse. This, then, constitutes the second kind of sequence in the notes of the human voice. Musical notes constitute the third mode of sequence. In music the sound has the requisite number of vibrations, and as the sounds succeed each other they exhibit that relative proportion in the number of vibrations which jointly characterize the notes of the musical scale. Of the adaptation of one sound to succeed another, so as to preserve the musical character of the succession, the human ear is the only original standard.

Compass of the Voice.-In singers the compass of the voice extends through two or three octaves. When the male and female voices are taken together, the entire scale of the human voice includes four octaves. The lowest note of the female voice is about an octave higher than the lowest of the male voice; the highest of the female voice is about an octave higher than the highest of the male. The first four notes of all voices are most commonly weak. There are two kinds of male voice, the bass and tenor; and two kinds of female voice, the contralto, and soprano. The essential dis

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DIFFERENCE BETWEEN THE MALE AND FEMALE VOICE.

tinction between these voices does not consist in their difference of pitch. The bass voice commonly reaches lower than the tenor, and its strength lies in the low notes; while the tenor voice extends higher than the bass. The contralto voice has most commonly lower notes than the soprano, and is strongest in the lower notes of the female voice; while the soprano voice reaches higher in the scale. It is found, however, that bass singers can sometimes go very high, and the contralto not unfrequently sings the high notes like soprano singers. The difference between the bass and tenor voice, and between the contralto and soprano, is plainly, then, not one of pitch, but consists in the peculiar timbre or quality of the notes-for these several voices are distinguished from each other even when sounding the same note. The qualities of the baritone and mezzo-soprano voices are less marked; the baritone being intermediate between the bass and tenor, the mezzo-soprano between the alto and soprano.

The difference of pitch between the male and female voice is connected with the different length of the vocal ligaments in the two sexes. It appears that the lengths of the male and female vocal cords in repose are nearly as 7 to 5, and in tension as 3 to 2; in boys at the age of fourteen the length is to that of females, after puberty, as 6.25 to 7,-so that the pitch of the voice is nearly the same. The difference in the quality of the female voice, as compared with that of the male, is owing to the considerable difference presented by the two sexes in the walls of the larynx; the male larynx being much more expanded, and forming a much more acute angle in front. It is not yet clearly understood what is the cause of the different qualities of voice, as exhibited in the tenor and bass, and the contralto and soprano. As Müller remarks: "We may form an idea of the cause of these differences of timbre, from recollecting that musical instruments made of different materials, as metallic and gut-strings, metallic, wooden, and membranous tongues, metallic, wooden, and paper pipes, or flutes, may be tuned to the same note, but that each will give it with a peculiar quality or timbre."

In short, when the variations of the larynx in different individuals of both sexes, and at different ages, under the various circumstances more or less favourable to the development of the respiratory organs, are considered, as well as the remarkable fact that every human being is characterized by a speaking voice peculiar to himself, we shall be at no loss to understand why the singing voice should vary in different persons, not only in pitch, but also in quality.

The voice termed falsetto has much engaged the attention of physiologists. Most singers, particularly males, besides their natural voice falling under one or other of the