Since Baas1 proposed the theory that vesicular breathing was only modified bronchial breathing, two different opinions have prevailed as to the origin of the breath sounds. According to one theory, the specific vibration of the porous tissue of the lung put in motion through respiration causes vesicular breathing; the second theory, like that of Baas, maintains that the vibrations of the bronchial system alone force their specific frequency on the tissues of the lungs and on the chest wall, respectively, being there either weakened or strengthened, according to the physical conditions of the vibrations of the air and of the conducting tissue of the lung. To the latter process, the laws of the so-called forced vibrations, as first proved by O. Frank,2 should be applicable. These laws may be of interest:
1. A correct conduction of the sound is possible only if the specific sound and the specific frequency,3 respectively, of