Should the specimens be very successfully dissected, it may be worth while to keep them for future observation, in rather weak alcohol (40 per cent.), in, say, a preserve jar.
All examinations of the vocal bands may leave the observer disappointed; he may fail to realize, most likely, how such wonderful results can be accomplished by structures so simple as those he sees before him. But when the laryngoscope is brought into use, then comes a revelation. This instrument will be described in the next chapter.
HYGIENE.
Some of the hygienic principles involved have already been referred to and ill.u.s.trated, and others follow from the facts already set forth.
It is very important for the voice-user to bear in mind that his larynx is a part of the respiratory tract, and that the whole of this region and the entire digestive tract, part of which is common to both, are lined with mucous membrane. If the nose be affected with catarrh, the throat does not usually long escape; and if the back of the mouth cavity (_pharynx_) be disordered, the vocal bands and other parts of the larynx are almost sure to be involved more or less.
The condition of the stomach is reflexly, if not by direct continuity through the mucous membrane, expressed in the throat generally; hence as experience shows, the voice-user cannot exercise too great care as to what and how much he eats, especially before a public appearance.
He must know himself what best suits him, in this regard, to a degree that is necessary for few others.
When singing, more blood is sent to the organs used, hence the great danger of that excess of blood being retained in the parts too long, as might easily happen from pressure about the neck, etc. It is scarcely necessary to point out that draughts, cold rooms, etc., will also determine the blood from the skin inward, and set up that complicated condition of multiform evils known as "a cold." The obvious principle of prevention lies in keeping the body, and especially the neck, shoulders, and chest, warm after using the vocal organs in any way in public. To hand the singer a wrap after leaving the platform is always wise, and the judicious friend will see that conversation is not allowed, much less forced on the possibly breathless and wearied voice-user--a precaution that is probably more honored in the breach than in the observance, for in this as in other cases one"s friends are sometimes his worst enemies.
SUMMARY.
The larynx is the most important organ in voice-production, and consists of cartilages, muscles, the vocal bands, true and false, membranes and ligaments, folds of mucous membrane, etc. It is situated between the hyoid (tongue) bone above and the trachea below. The cartilages are the (1) epiglottis, (2) thyroid, cricoid, arytenoid, the two small, unimportant cornicula laryngis, or cartilages of Santorini, surmounting the arytenoids, and the two cuneiform, or cartilages of Wrisberg, in the folds of mucous membrane on each side of the arytenoids.
The muscles are attached to the main cartilages. In addition to the muscles that are concerned with the movements of the vocal bands, others that hold the larynx in place or raise and lower it are attached _externally_ to these, especially to the large thyroid cartilage. The epiglottis, the false vocal cords, the true vocal cords, and the thyro-arytenoid muscles are attached to the interior anterior surface of the thyroid in this order from above down.
The false vocal bands have no direct function in phonation. _The whole larynx, so far as phonation is concerned, may be said to exist for the true vocal bands._ They are attached close together to the internal and anterior surface of the thyroid in front and to the lower anterior angles (vocal processes) of the arytenoids behind. Between the false vocal bands above and the true vocal bands below there is a cavity (the ventricle of Morgagni). The false vocal bands are protective, and approximate closely during coughing, swallowing, etc.
It is very important to note that the arytenoid cartilages move freely on their base, swivel-like, so that nearly all the changes effected in the movements and tension of the vocal bands are brought about through alterations in the position of these cartilages; and this implies that all the muscles concerned are attached to them. From above down, in front, the order of structures is as follows:
Hyoid bone.
Membrane.
Thyroid cartilage.
Membrane.
Cricoid cartilage.
Trachea.
The hyoid bone is not a part of the larynx, but from it the larynx is suspended. The bone itself gives attachment to the muscles of the tongue. The glottis is the c.h.i.n.k between the true vocal bands.
The muscles of the larynx may be divided into the following: (1) Those that open and those that close the glottis; (2) those which regulate the tension of the vocal bands. The latter include the (_a_) crico-thyroids, which tense and elongate them, (_b_) thyro-arytenoids, which relax and shorten them. The crico-thyroid may be considered the most important muscle of phonation, because it is so much used and so effective. By its action the cricoid is pulled up in front and down behind, so that the arytenoids are drawn back, and thus the vocal bands tensed and lengthened. The lateral crico-arytenoids and the thyro-arytenoids have the opposite effect--_i.e._, they relax and shorten the vocal bands; hence when they come into play a new register begins. The thyro-arytenoids, attached along the whole length of the vocal bands externally, have a very important but not well-understood action in the production of the higher tones, and probably also of the falsetto.
The whole larynx is lined with mucous membrane, that covering the true vocal bands being very thin. The false vocal bands are made up chiefly of mucous membrane; the true vocal bands abound in elastic tissue. The larynx rises during the production of high tones, and during phonation its vibrations may be felt, as also those of the chest.
_Practical._
1. Feel in your own person the parts of the larynx, etc., from above down.
2. Note the vibration of the larynx when a vowel is spoken or sung. A similar vibration of the chest walls may be felt by the hands laid over them.
3. Note the change of position of the larynx in singing a scale.
4. Dissect a pig"s or sheep"s pluck and some specimens of the larynx.
[Ill.u.s.tration: FIG. 35. These three figures ill.u.s.trate perhaps more clearly the _action_ of the muscles indicated FIGS. 26-34.
The arrows show the direction of the pull of the muscles. The result of this action is the new position of the cartilages and vocal bands, which is shown by red outlines. The muscle is also depicted in red.
The heavier outer rim is to indicate the thyroid cartilage. By comparing the upper and the lowest figure it will be seen that they are opposites. Of course, in phonation the vocal bands are never so much separated as shown in the ill.u.s.trations. Rather does the lower figure indicate a case of extreme separation due to a very deep inspiration. However, these ill.u.s.trations are merely diagrams meant to indicate in a general way the manner of the working of parts. For exact pictures of the vocal bands and related parts, see Chapter VII.]
CHAPTER VII.
SOUND--THE LARYNGOSCOPE--THE LARYNX RECONSIDERED.
Before discussing our subject further it is desirable that some attention be given to a few of the fundamental principles of that department of physics termed _acoustics_, and which deals with the subject of sound. If the student has the opportunity to study this subject theoretically and practically, as it is set forth in some good work on physics, he will have no reason to regret the time spent. A deep knowledge of the laws of sound is not absolutely essential, or even highly necessary, for a sufficient understanding of the principles involved in voice-production. It is, however, all-important that a few facts and principles be thoroughly grasped.
For those who feel that they have the time for a study of acoustics, the author would especially recommend Tyndall"s work on sound, in which the subject is treated with wonderful clearness and charm. What we endeavor now to bring before the reader we have found sufficient for nearly all the purposes of the voice-user.
An observer on the street, looking at a military band, notices certain movements of one member of the organization which result in what he termed the sound of the drum; but a deaf man by his side, though he sees the movements, hears nothing. This, being a.n.a.lyzed, means that the movements of the drummer"s arm, conveyed through the drumstick to the membrane of the drum, give rise to movements in it which set up corresponding movements of the air within the drum, which again cause movements of the body of the instrument, the whole causing movements of the external air; and here the purely physical process ends. The movements other than muscular ones are not readily observed, but experiments not only prove that they exist, but demonstrate their nature, even to their exact rate of occurrence, their size, etc. These movements are termed _vibrations_, and, as has been indicated previously, they are the sole physical cause of sound. But that the latter is not due wholly to a physical origin is evident from the fact that sound for the deaf does not exist. It must, therefore, be a personal, a subjective experience, and as the sleeping, unconscious person does not necessarily hear a sound, the process is not wholly a corporeal or physiological process; it is finally an experience of the mind, the consciousness, and so is psychological as well as physiological.
The fact that sound has a physical basis in the vibrations of bodies, either solid, liquid, or gaseous, may be brought home to one in various ways. Concussion or shaking of some kind is essential to start these vibrations. The air is made up of its particles, and one being moved sets up, inevitably, movements in neighboring particles on all sides, hence vibrations travel in all directions; which explains why a sound in the street may be heard by those in every part of the street not too distant, and also in the upper rooms of the houses and below in the bas.e.m.e.nts. This is an important fact for the singer or speaker to bear in mind. His purpose must be to set up vibrations that will travel with great perfection and rapidity in all directions.
The following experiments of a simple kind will serve to convince those who may not have given much attention to the subject that sound is due to movements of some object, which we term the sounding body, strictly that which starts the vibrations by its own movements or vibrations.
If a sufficiently flexible band of metal or a stiff piece of whalebone be fixed at one end in a vice, and then sharply pulled to one side and suddenly let go, a sound results. The same effect is produced when a tight cord or small rope is plucked at and then suddenly released. In each of these cases, if actual movements are not seen, a certain haze which seems to surround the object may be observed. The same can be seen when a tuning-fork is set into action by a bow, a blow, etc. In the case of the fork a graphic tracing (Fig. 36) can be readily taken on smoked paper, thus demonstrating to the eye that vibrations exist, that they occur with perfect regularity and with a frequency that can be measured.
[Ill.u.s.tration: FIG. 36 (Tyndall). Ill.u.s.trates how the vibrations of a tuning-fork are registered on a blackened (smoked) gla.s.s. In order that the movements of the fork shall be traced in the form of regular curves, the surface must be kept moving at a definite regular rate.]
A similar observation can be made in the case of stringed instruments.
If pieces of paper be laid on the strings of a violin, and the bow then drawn across them, the bits of paper will fly off owing to the movements--_i.e._, the vibrations--of the strings.
That a force applied at one end of several objects in a line or series causes an obvious effect at the other end, can be well ill.u.s.trated in a simple way. If a number of individuals stand one behind another in a line, each with his hands laid firmly on the shoulders of the one next to him, and the person at the end be pushed, the force will be conveyed through all the intermediate individuals, and cause the unsupported person at the distant end to move. So is it with the particles of which the air is composed. The movements begun in the drum set up by contact corresponding movements or vibrations in the adjacent air, which ultimately reach the hearing subject"s ear, thereby affect his brain, and are accompanied by that change in consciousness which he terms "hearing." It will be observed that these events const.i.tute a chain, and a break anywhere will prevent a sound being heard; there is then, in fact, no sound.
Sounds are characterized by _pitch_, _volume_, and _quality_.
The _pitch_ is determined by the number of vibrations that reach the ear within a certain time; the more numerous the sound-waves (vibrations) in a second, the higher the pitch.
[Ill.u.s.tration: FIG. 37 (Tyndall). Meant to ill.u.s.trate vibrations. The impulse communicated by the ball pushed from the hand to all the intervening ones causes only the last to actually move bodily.]
Animals differ a good deal as to the limits of hearing. Cats hear very high-pitched sounds, as of mice, that human beings may not notice, and it is likely that insects hear sounds altogether beyond the limit of the human ear. But it is wonderful how much human beings differ among themselves in regard to this matter. It has surprised the author to find that many persons cannot hear the high-pitched note of certain birds, as the wax-wing.
The lower limit, speaking generally, is for most persons 16 vibrations, and the highest 38000 vibrations a second, according to Helmholtz, hence the entire range of the human ear would be fully 11 octaves; but the practical range of musical sounds is within 40 and 4000 vibrations a second--_i.e._, about 7 octaves--and, as is well known, even this range is beyond the appreciation of most persons, though as to this much depends on cultivation--attention to the subject extending over a considerable period of time.
The _volume_, or loudness, of a sound depends on the size of the vibrations, just as one feels a blow from a large object, other things being equal, more than from a small one. The ear drum-head is in the case of a large sound beaten, as it were, more powerfully. The singers that give us bigness of sound instead of quality belabor our ears, so to speak; they treat us as persons of mean understanding--dull intellects; the thing is essentially vulgar.
The _quality_ of a sound is determined by the form of the vibrations.
A sound of good quality is to the ear what a beautiful statue or picture is to the eye. As will be explained later, the form or quality depends largely on the shape, etc., of the resonance-chambers above the vocal bands.
Much discussion has taken place from time to time as to the nature of the larynx as a musical instrument, some being inclined to regard it as most closely allied to a stringed instrument, others to a wind-instrument. It has obviously points of resemblance to both, but the most recent researches make it clearer than ever that it is neither one nor the other, strictly speaking, but that it stands in a cla.s.s by itself. It is, however, helpful, in considering many questions, to bear in mind its resemblances to both wind and stringed instruments. The vocal bands are not wholly free throughout their length, like the strings of a violin, nor do they bear any great resemblance to the reed of such an instrument as the clarinet, but as in the latter the force causing the vibrations is a blast of air. We have already pointed out that the vocal bands are set into vibration solely by the _expiratory_ blast of air.