For the purposes of this paper bronchiectasis is considered primary when the ulceration and dilatation of the bronchial tree cannot be ascribed to any preceding or underlying pathologic process in the lungs or bronchi. Thus I have excluded from consideration all lesions occurring in the course of tuberculosis: both the true tuberculous ulcerations of the bronchial wall and the more common forms of bronchial dilatation seen in chronic fibroid phthisis, in lungs collapsed by artificial pneumothorax or by thoracoplasty, and in old atelectatic lungs. The latter lesions are usually mere mechanical dilatations due to the stretching and distortion of the bronchi by fibrous tissue, and, on section, the bronchial wall is seen to be intact, in contrast to primary bronchiectasis in which ulceration and destruction of the elastic tissue are conspicuous. The definition also excludes bronchiectasis secondary to stricture of the bronchus due to aneurysm, neoplasm or foreign body, as