Page:Popular Science Monthly Volume 36.djvu/110

100 case of the muscles moving the chest and the vocal cords naturally produced sound—that is to say, voice. These movements, at first accidental and purposeless, in time became inseparably associated with the emotional state giving rise to them, so as to coincide with it, and thus serve as an index or expression thereof. From this to the voluntary emission of vocal sounds is an easy step, and it is probable enough that the character of those sounds was primarily due to the "imitation and modification of different natural sounds, the voices of other animals, and man's own instinctive cries."

The mechanism of the voice is extremely simple in its general principles, though highly complex in its details. Fortunately, a knowledge of the latter is not required for the comprehension of the main facts relative to the production of the voice, and I shall not further allude to them here. Vocal sound is produced solely in the larynx, an elementary fact which must be thoroughly grasped, as many absurd notions are current even among people who should know better, such as that the voice may be produced at the back of the nose, in the stomach, and elsewhere. The larynx is a musical instrument of very complex structure, partaking both of the reed and the string type, the former, however, distinctly predominating. It is essentially a small chamber with cartilaginous walls, which is divided into an upper and a lower compartment by a sort of sliding floor, or double valve, formed by the two vocal cords. In breathing this valve opens, its two lateral halves gliding wide apart from each other, so as to allow a broad column of air to pass through; in speaking or singing, on the other hand, the valve is closed, but for a narrow rift along its middle. Through this small chink the air escaping from the lungs is forced out gradually in a thin stream, which is compressed, so to speak, between the edges of the cords, that form the opening technically called the "glottis," through which it passes. The arrangement is typical of the economical workmanship of Nature. The widest possible entrance is prepared for the air which is taken into the lungs, as the freest ventilation of their whole mucous surface is necessary. When the air has been fully utilized for that purpose, it is, if need be, put to a new use on its way out for the production of voice, and in that case it is carefully husbanded and allowed to escape in severely regulated measure, every particle of it being made to render its exact equivalent in force to work the vocal mill-wheel. When the air is driven from the lungs up the windpipe it strikes against the under surface of the floor or double valve formed by the vocal cords, which are firmly stretched to receive the shock, forces them apart to a greater or less extent, and, in rushing out between them, throws them into vibration.