The distinguished physiologist Johannes Mueller demonstrated the working of the larynx by special experiments. He fixed into the windpipe a bellows, and showed, in the dead larynx, of course, that the blast from this source could cause the vocal bands to vibrate and thus produce sounds, which by varying the strength of the force, etc., were made to vary in pitch. While such experiments indicate the essential principles of a possible voice-production, as the conditions in life were not and could not be fully met these results were rather suggestive than demonstrative of Nature's methods. These investigations served a good purpose, but they were manifestly inadequate, and this was felt by one thoughtful vocal teacher so keenly that he pondered much on the subject, in the hope of finding a method of observing the larynx during actual phonation. To this distinguished teacher, Manuel Garcia, belongs the honor of inventing the means of observing the vocal bands in action. This was accomplished in 1854, and, soon after, Garcia read an account of his observations to the Royal Society of London; and though much in this paper required correction by subsequent observations, it remains to this day the foundation of our knowledge of the action of the larynx in voice-production. [Illustration: FIG. 38 (Bosworth). Intended to illustrate the optical principles involved and the practical method of carrying out laryngoscopic examination. The dotted lines show the paths of the light-rays.] As usually employed, the laryngoscope consists of two mirrors, the head-mirror, so called because it is usually attached to the forehead by an elastic band, and the throat-mirror, which is placed in the back part of the mouth cavity. The purpose of the head-mirror is to reflect the light that reaches it from a lamp or other source of illumination into the mouth cavity so perfectly that not only the back of the mouth, etc., but the larynx itself may be well lighted up; but inasmuch as this illumination may be accomplished, under favorable circumstances, by direct sunlight, the head-mirror is, though mostly indispensable, not an absolutely essential part of the laryngoscope. There is, indeed, one advantage in the use of direct sunlight, in that the color of the parts seen remains more nearly normal. Lamplight tends, because of its yellow color, to make parts seem rather of a deeper red than they actually are; but this to the practised observer, always using the same source of illumination, is not a serious matter--his standards of comparison remain the same. Moreover, this objection does not apply equally to electric light, now so much used.