Page:Popular Science Monthly Volume 9.djvu/414

390 in an appendage called the uvula. When the velum palati, or soft palate, does not discharge its functions properly, the voice assumes a specially disagreeable character—it becomes nasal. The two rows of teeth act a part in producing speech; a breach once made in this rampart, the pronunciation becomes defective, the air escapes through the unguarded space, and the result is a hissing sound.

The plan of action of the whole vocal apparatus being under investigation, in the absence of the means of direct observation, recourse has been had to endless stratagems, in order to have a glimpse of the play of the organs and to explain the mechanism of voice-production. It has been a struggle with incredible difficulties, in which the human mind, though it has not won a complete victory, has nevertheless acquitted itself with honor. Some of the investigators succeeded in forming theories which are not very far from the truth, but these theories are now only the monuments of a period whose science is antiquated.

Galen, in comparing the organ of voice to a flute with double mouth-piece, referred the production of the sound to the vocal cords. Fabrizio d'Acquapendente, the famous professor of the University of Padua, held that the dilatation and contraction of the glottic orifice determined whether sounds shall be grave or acute. Dodart, a member of the old Académie des Sciences, held that the tone depends upon the greater or less number of vibrations of the vocal cords. Ferrein, one of the famous anatomists of the eighteenth century, conceived the idea of causing the larynx of a dead body to produce sounds by blowing through the trachea. He affirms that the lips of the glottis vibrate and emit sound like the strings of a violin. Magendie made experiments upon living animals; having laid bare the glottis, he saw the vocal cords vibrating when the animal uttered a cry. Savart, famed for his researches in acoustics, compared man's vocal apparatus to an organ-pipe. Lehfeld, a German author, laid stress upon the special effects of the cords, as vibrating through their entire substance, or only at their free edges. Cagniard de Latour constructed artificial larynges with mouth-pieces of membrane. John Müller, the physiologist, after a series of diversified researches, was of the opinion that "the vocal organ is a mouth-piece consisting of two lips, and that the vibrations of these is the chief cause of the sound—the pitch being determined by the width and length of the orifice of the glottis." Longet, who made numerous experiments on the actions of the muscles of the vocal organ, threw new light upon the conditions modifying the vibrations. In short, the result of all these researches, made by investigators who never had seen the larynx of a living man, was firmly to establish one point, namely, that the voice is formed in the glottis. The proofs of this are conclusive, for, if an opening be made in the trachea, the voice ceases; it reappears when we close the opening again; it persists though the superior parts