Transactions of the Medical Society of King's College, London.

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Credit: Transactions of the Medical Society of King's College, London. Source: Wellcome Collection.

    124/262 (page 114)
    the production of sound; and where a stethoscope is placed over the trachea, the sounds of the voice are transmitted to the ear, as if the mouth of the speaker were applied to the ear.— 3. As the pitch of the voice varies, the dimensions of the vocal tube also vary.—4. The pitch of the voice, like that of flute pipes, varies with the density of the gas which we respire; thus, a person who has inhaled some hydrogen speaks several tones higher than his natural voice. These facts, I think, amply show that the trachea and its contained column of air participate in the production of the voice. It ought to be observed, that, in tubes composed of flexible material, like the trachea, the parietes of the tube vibrate conjointly with the enclosed air, and give forth much graver sounds than rigid tubes of the same length in which the column of air alone vibrates. This explains how the short tracheal tube can yield the deep notes of the human voice. In many birds, the voice is entirely due to the vibrations of the column of air in the trachea, excited by friction against the lips of an opening. M. Savart compared the human larynx to a bird-call, which is considered to belong to this class of instruments. It is formed of a very short cylinder of ivory or metal, covered at each end with a perforated plate: by blowing through one aperture, the wind contained in the cavity of the instrument is thrown into vibration, and sound produced. The larynx certainly bears a considerable resemblance to this instrument. The true and false vocal cords, with the chink between each of them, are analogous to the perforated plates; while the ventricles form the cavity of the instrument. M. Savart con¬ sidered that the air rushing between the vocal cords set in motion the air in the ventricles, which produced the sounds of the voice. This theory is quite untenable; since, in many ruminantia which have remarkably sonorous voices, the upper