This section is from the book "Human Physiology For The Use Of Elementary Schools", by Charles Alfred Lee. Also available from Amazon: Human Physiology, for the Use of Elementary Schools.
14. The strength of the voice depends on the extent of the vibrations, of course on the size of the larynx, and partly also on the fores with which the air is sent from the lungs. Thus the voice of men is much stronger than that of women and children ; and that of a well person stronger than that of a feeble individual. The change of voice at the period of manhood, is owing to the increase in size of the larynx.
15. The tone of the voice can be almost infinitely varied : indeed, nothing can exceed the human organ of voice in variety and execution. We may perhaps safely calculate the number of changes that can be produced in the organ, at least to be equal to the number of muscles employed, together with all the combinations of which they are capable. Now, the muscles immediately concerned in the function of voice are seven pair. Besides these, however, there are fifteen other pair, which are connected with the larynx, and have more or less to do in regulating the motions of the cartilages, keeping them steady or moving them in different directions.
16. Now, if there were only seven pair of muscles concerned, the different movements which their varied action would produce, will amount to more than sixteen thousand. Taking the whole number of muscles into account, the different combinations will be more than one thousand million. But besides these, there are the midriff, or diaphragm, the ahdominal, and the intercostal muscles, all of which are concerned in the production of voice ! " How wonderful is man! How passing wonder, He that made him such !"
17. The precise manner in which such an infinite variety of tones is produced, is unknown ; physiologists explaining the matter according to.their respective theories, whether the larynx be a wind or stringed instrument. The glottis doubtless contracts for the production of acute or sharp tones ; but how grave ones are produced, admits of doubt, whether it be owing to a lengthening of the trachea, or the relaxation of the vocal chords. Perhaps it would be near the truth to say, that both these circumstances take place, but that the grave notes are chiefly caused by the latter.
18. Ventriloquism consists in making the voice appear to proceed from other persons in various places, either in or out of the room. To do this with success the performer first directs the attention of the audience to the place from whence he wishes to have his voice appear to proceed; he then changes his voice in such a manner as makes it sound like that of another person, or the noise of the animal he designs to imitate, and in doing so, avoids all the words which have labials, or which require the use of the lips. This modification of voice is supposed to be performed by the muscles of the larynx, and this is known to be the sole organ of all the natural cries.
19. There are generally considered to be two kinds of voice, the natural and acquired. The former is possessed in common with man, by the inferior animals, but the latter is enjoyed by man alone to any extent. The natural voice consists in mere cries, and is possessed by the infant as soon as it is born, and also by idiots, and by those who are born dumb. It is seated entirely in the larynx, and does not depend on intellect, or hearing.
20. The acquired voice, on the contrary, is the result of imitation, and enables us to express our ideas in words or articulate sounds. In this way the child learns to imitate the sounds which he hears, and if he is deaf, of course he will never learn to speak : children therefore are dumb, because they are deaf. Idiots also are dumb, although they can hear; intellectual faculties, therefore, are necessary to speech as well as hearing; and it is probably owing to a want of intellect that infants do not speak at an earlier age. For the same reason, the ourang outang cannot acquire the faculty of speech. In the acquired voice, the tongue and lips are brought into exercise, but neither of them can be regarded as absolutely essential to the faculty of speech.
21. Whistling is caused by the expired air being broken or divided by the lips, which act the part of the glottis in the production of the voice. Whispering consists in the articulation of the air of expiration, and is wholly performed in the vocal tube ; hence the impossibility of singing in a whisper-singing being produced in the glottis. Sighing is produced by the rushing of the air along the air passages; and the voice is also concerned in laughing, crying, coughing, sneezing, yawning, and sobbing, modified by the mode of respiration.
22. Singing is a very useful art, and ought to be learned by every person. It not only contributes to our intellectual gratification, but is also of essential benefit to the bodily health. For these reasons, and because it conduces to beget an habitual cheerfulness of mind, it ought to be taught in all schools and academies, and made a part of the daily exercises, as it is in Germany, and in our own infant schools.
What is voice ? Where is its seat ? What is the larynx composed of ? What is the shape of the thyroid cartilage ? Describe its structure ? The cricoid ?-its structure and situation ? Describe the arytenoid cartilages ? What is the glottis ?-the epiglottis ? What is the thyroid gland ?-its use ?-the seat of what disease ?
What does the whole vocal apparatus comprise ? What is essential to the production of voice ? What effect has cutting the nerves which go to the larynx ? What part of the larynx can be removed without effecting the voice ? What are chiefly concerned in the production of voice ? Is the larynx a wind or stringed instrument ? What does the strength of the voice depend on ? What is a change of voice owing to ? What is said of the tone of the voice ? How many muscles are concerned ? How many combinations can they produce ? How are acute sounds produced ? How grave ones ? What is ventriloquism ? What is natural voice ? What acquired ? Why are deaf children dumb ? Why are idiots ? What is whistling ?-whispering ?-sighing, &c? What is said of singing ?