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A detailed account of the various existing theories of the produc­tion of the respiratory sounds may be found in Dr. Paul Niemeyer’s “Handbuch der Percussion und Auscultation” (Erlangen, 1870). The various theories, though differing in minor points, may be arranged under three principal heads. A. According to the first the sounds are produced all along the respiratory tract by the friction of the air against its walls. B. According to the second the sounds are produced at the glottis alone, and the differences in the sounds heard over the trachea and lungs are attributed to the greater or less conducting power of the structures through which they are heard at each spot. C. According to the third theory the sounds are produced at those parts of the respiratory tract where the air passes from a narrower to a wider space. Thus during inspiration one sound is produced at the glottis, and another at the points where the smallest bronchioles open into the vesicles; During expiration a sound is produced at the glottis only.

II. Experiments to determine the origin of the respiratory sounds