It is only within relatively recent years that the importance of bronchial obstruction for the production of a wide variety of pulmonary diseases has come to be more generally recognized. True, in frank foreign body obstruction of a bronchus, it has been known that absorption of the air and atelectasis can ensue. Aside from advancing the therapy of this type of obstruction, Chevalier Jackson was the first to recognize atelectasis as a symptom of bronchial obstruction by diphtheritic membranes and to cure so-called diphtheritic pneumonia by bronchoscopic aspiration. William Pasteur in 1890 had noticed the frequent occurrence of atelectasis ("massive collapse") of the lung in diphtheria, but ascribed it etiologically to paralysis of the diaphragm, which he thought could bring about the airless state of the lung. In Pasteur's cases the high diaphragm was the result and not the cause of the condition; for it is well known today that