Page:Popular Science Monthly Volume 64.djvu/268

264 In the voice, as in other forms of sound, we must have, first, a vibrating body to initiate the sound. This we have in the vocal cords of the human body. The vibrations set up in the vocal cords (Fig. 1) are not due to a violent impact, as in the case of the tuning fork, as this would injure the delicate tissues of the sound-producing organs, but are caused by the air passing between the vocal cords very much as the current of air sets up vibration in a reed instrument such as the clarionet. In the human voice this current of air is furnished by the lungs, which have therefore the double duty of supplying the oxygen to the blood and setting up vibrations in the vocal cords for the voice.

The chest is supplied with the most perfect mechanism for obtaining this current of air. The main support is furnished by the ribs, which give firmness to the chest. These are held together and supported by muscles of great strength which raise the ribs in the act of inspiration. The lower part of the chest is enclosed by a broad flat muscle known as the 'diaphragm,' which materially assists in giving its bellows-like faculty to the chest. In the act of inspiration, the diaphragm is lowered and the ribs are raised, thus creating a space in the lungs which is filled by the air entering through the nose and throat. In expiration, however, this is reversed, the ribs being lowered and the diaphragm raised, the process being assisted by the natural elasticity of the lung tissue. The thorough understanding of this function of the lungs should impress us with the importance of not hampering their action by tight clothing or lacing, which necessarily interferes with their freedom of action, and, by thus lowering the resistance of the body, make it more liable to the entrance of disease.

The two vocal cords, whose vibration forms the essential factor in the voice, are situated within the larynx, the most prominent point of which is known as the 'Adam's apple.' The larynx has several plates of cartilage which, while protecting the delicate organs within, make it less liable to fracture or injury than if they were made of bone. By removing one of the plates of the larynx, we see the edge of one of the vocal cords, which consists of a narrow band of rather hard tissue, whitish in color in health, and surmounted on a band of muscles which not only gives it support but also enables it to adjust the tension necessary for tone-formation. The vocal cords, during