VOICE (Lat. vox) may be defined as an audible sound produced by the larynx, and may be produced by any animal possessing that organ; while speech or articulate lan guage may be regarded as voice modified in the cavity of the mouth. The larynx (q.v.) is the organ by which the so-called vocal sounds (or primary elements of speech) are pro duced. In the article LARYNX, it is shown that there are two groups of muscles, which respectively govern (1) the pitch of the notes, and (2) the aperture of the larynx. Those which affect the pitch of the notes are divisible into two antagonistic sub-groups, viz., (a) those which depress the front of the thyroid cartilage on the cricoid, and stretch the vocal ligaments; and (b) those which elevate the front of the thyroid cartilage, and relax: the vocal ligaments; while those which control the aperture of the glottis are divisible into (c) those which open it, and (d) those which close it. It is only the first of these groups, viz., the muscles which stretch or relax the vocal ligaments, that is concerned in the production of voice. In the ordinary condition of rest there is a wide opening between the vocal ligaments, which are in a state of complete relaxation, and the air passes freely between them. For our knowledge of the appearances presented under varying conditions by the interior of the larynx, we are mainly indebted to prof. Czer mak, the inventor of the laryngoscope (q.v.); and the reader who wishes to enter fully into this subject is referred to his work on that instrument, of which a translation was published by the New Sydenham society in 1861. The movements of the arytenoid car tilages during the production of vocal sounds can be distinctly seen—the views that had been previously deduced, from theory and experiments on the dead subject, being thus confirmed by ocular proof. As soon as we wish to utter a sound, the two arytenoid car tilages raise themselves in the fold of mucous membrane which covers them, and approach one another with surprising mobility. This movement effects the approxima tion of the vocal cords, and consequently the contraction of the glottis. It is impossi ble to study with the laryngoscope the mode of formation of the gravest chest-sounds, because the arytenoid cartilages become so raised that they almost come in contact with one another, while they bend under the border of the depressed epiglottis, and thus con ceal the interior of the larynx. During the emission of the most acute sounds, the glot tis contracts into a mere line,on each side of which the vocal cords may be recognized by their whitish-yellow color; while further outward, and separated from the former by a narrow groove, are the false or superior vocal fiords of either side. The arytenoid car tilages are raised, and come in contact in the median line, the epiglottis is drawn outward, and a short stiff tube is then formed above the glottis; all these parts being, as we learn. from our sensations during the experiment, in a state of very great tension. Independ ently, however, of such observations as those we have recorded from Czermak's inter esting memoir, any one may easily prove for himself that the aperture of the glottis is much contracted during the production of sounds by comparing the time occupied by an ordinary expiration with that required for the passage of the same quantity of air during the maintenance of a vocal sound; moreover, the size of the aperture varies with the note that is being produced, as may be readily seen by any one who compares the time during which he can hold out a low and high note. When the distance between the vocal cords exceeds one-tenth of an inch, uo sound can be produced.
How the vocal cords produce sounds is a question which has long attracted the atten tion of physiologists and physicists. To answer it they were compared with various musical instruments. More than a century ago Ferrein (De la Formation de la Voix de
Ukraine, 1741) compared them to vibrating strings; and, at first sight, there is an appar ent analogy; hot on further investigation (for reasons which may be found in Carpenter's Human Phyx. logy, 6th ed. p. 715), this view was found to be untenable. The ana logues between the organ of voice and the flute-pipe, in which the sound is produced by the vibration of an elastic column of air contained in a tube, were then investigated, but found to fail. The third class of instruments with which the human organ of voice has been compared are vibratory reeds or tongues, which may either possess elasticity in themselves, or be made elastic by tension. From the experiments of Weber it appears that the action of the larynx has more analogy to that of reed-instruments than to the instruments previously named, and though there would seem at first sight to be a marked difference between the vocal ligaments and the membranous tongue of any reed-instrument, this difference is not very. great. Miler ascertained that membranous tongues made elastic by tension may have three different forms, of which the following, which alone.eoncerns us, is one: "Two elastic membranes may be extended across the mouth of a short tube, each covering a portion'of the opening, and having a chink left open between them." Here there is clearly an approximation to the human glottis, which may be increased by prolonging the membranes in a direction parallel to that of the current of air, so that not merely their edges but their whole planes shall be thrown into vibration. Prof. Willis has, upon this principle, invented an artificial glottis, in which the vocal ligaments are imitated by leather, or preferably by sheet It is composed of a wooden pipe of the form of having a foot, C, like that of an organ pipe, and an upper opening, long and narrow, as at B, with a point, A, rising at one end of it. A piece of leather or sheet India-rubber doubled round this point, and secured by being bound at D with strong thread, will form an artificial glottis, b, while its upper edges, G, H, are capa ble oi! vibrating or not by inclining the planes of the edges. Two pieces of cork, E and F, are glued to the corners to make them more manage able. From this machine various notes may be obtained by stretching the edges of the leather in the directions of their length, G, H; the scale of notes yielded by leather is much more limited than that yielded by india-rubber; and other observers have found that the middle coat of the arteries in a most state (as being more elastic, and almost identical in structure with the vocal ligaments), yields more satisfactory results even than india-rubber. "It is worthy of remark," as Dr. Carpenter observes, "that in all such experiments it is found that the two mera branes may be thrown into vibration, when inclined toward each other in various degrees, or even when they are in parallel planes, and their edges only approximate; but that the least inclination from each other (which is the position the vocal ligaments have dur ing the ordinary Mate of the glottis) completely prevents any sonorous vibrations from being produced."—Op. cit., p. 718. The pitch of the notes produced by membranous tongues may be affected in various ways (as by the strength of the blast, the addition of a pipe, etc), and is mainly governed by their degree of tension, while the foregoing statements show that the sound of the voice is the result bf the vibrations of the vocal ligaments which take place according to the same laws with those of elastic tongues generally. Little is, however, known with certainty regarding the mode and degree in which the tones are modified by the shape of the air-passages generally, the force of the blast of air, and other circumstances.