In most cases there will be limitation of expansion on the invaded side, even though the foreign body is of such a shape as to cause no bronchial obstruction. It has been noted frequently in conjunction with the presence of such objects as a common straight pin in a small branch bronchus. This peculiar phenomenon was first noted by Thomas McCrae in one of the author's cases and has since been abundantly corroborated by McCrae and others as one of the most constant physical signs. To understand the peculiar physical findings in these cases it is necessary to remember that the bronchi are not tubes of constant caliber; there occurs a dilatation during inspiration, and a contraction of the lumen during expiration; furthermore, the lumen may be narrowed by swollen mucosa if the foreign body be of an irritant nature. The signs vary with the degree of obstruction of the bronchus, and with the consequent degree of interference with aeration and drainage of the subjacent portion of the lung. We have three definite types which show practically constant signs in the earlier stages of foreign body invasion. 1. Complete bronchial occlusion. 2. Obstruction complete during expiration, but allowing the passage of air during the bronchial dilatation incident to inspiration, constituting an expiratory valve-like obstruction. 3. Partial bronchial obstruction, allowing to-and-fro passage of air. 1. _Complete bronchial obstruction_ is manifested by limitation of expansion, markedly impaired percussion note, particularly at the base, absence of breath-sounds, and rales on the invaded side. An atelectasis here exists; the air imprisoned in the lung is soon absorbed, and secretions rapidly accumulate. On the free side a compensatory emphysema is present.