218 THE LARYNX, BRONCHI AND OESOPHAGUS chewed nut, or a tack, for example, may only reach a major subdivision of a main bronchus, while a larger object, such as a peanut or a tooth, will be held up in the main bronchus itself. When a foreign body enters a bronchus, either the object so occludes the lumen that air entry to the distal segment is inadequate and segmental collapse takes place, or the foreign body becomes so lodged in the lumen that it allows the more powerful inspiratory stream of air to pass but it obstructs the expiratory stream, which is less strong and is impeded by bronchial contraction, with a resultant emphysema of the distal segment (Fig. 109). Fig. 109. Emphysema of left lobe due to a piece of nut in the lower lobe bronchus. On clinical examination the features of collapse are dullness on percussion and lack of air entry, while if decomposition has taken place with the produc- tion of an inflammatory reaction moist sounds will be heard. If there is distal emphysema there will be a prolongation of expiration in the affected lobe, and later hyper-resonance over that lobe. Radiography may be diagnostic. A radio-opaque foreign body will be seen (ftg. 110), and if anteroposterior, lateral and oblique views are taken its position may be accurately determined. A non-opaque foreign body, such as plastic or vegetable matter, is much more difficult to diagnose radiographically, and in the early stages the films may show no abnormality. It is important to realize this, and not to dismiss the possibility of an inhaled foreign body on the strength of a negative radiograph. Later there may be emphysema of a lobe CRj£. 109) or of a lung, while an occlusive non-opaque foreign body will eventually show the typical radiographic appearance of a collapse of one or more lobes of a lung, with a shift of the cardiac shadow to that side.