A note on the elastic membrane of the bronchial tree of mammals, with an interpretation of its functional significance

A note on the elastic membrane of the bronchial tree of mammals, with an interpretation of its functional significanceThe network of longitudinal elastic fibers which forms a inembrane in the tunica propria of the entire bronchial tree of maininals may be dissected off en niasse from the fresh trachea and larger bronchi, and the specimen so obtained may be stained, cleared, and mounted.Stout in the trachea, and especially in the larger bronchi, this elastic membrane becomes thin and delicate in t8he terminal twigs, where it unites with the elastic tissue of the air chambers.Considered in toto, its form reproduces that of the entire bronchial tree.The limbs and trunk of the bronchial tree constitute a system of extension and contraction axes for the movements of expansion and contraction of the lung.The filling and emptying of any considerable area of lung is inseparable from the stretching and contraction of the airway.The elastic membrane is by far the most efficient part of the recoil mechanism of the bronchial tree, and is a very important, if not the most important, part of the recoil mechallisin of the entire lung.Downward shifting of the lower part of the lung is necessary to free expansion of the upper part, and is associated with downward movement of the lung root and stretching of the bronchi and trachea.Pathological changes which tend to immobilize the lung roots or stiffen the bronchial tree will impair normal lung function, particularly in the upper lobe, and such changes may go far to account for the susceptibility of this part of the lung to tuberculosis.