The causes of obliteration of the bronchial tubes is not well understood, yet, they are more frequently observed in persons who have suffered repeated attacks of bronchitis, or of chronic pneumonia. =Dilatation of the Bronchial Tubes.= This condition of the bronchial tubes is more frequent in its occurrence than obliteration. It takes place in two forms, either several tubes are uniformly dilated, like the fingers of a glove, or a single tube may form a cavity, by undergoing a sacular enlargement. Some mechanical obstruction, by interfering with the free passage of air through the tubes, will usually have caused the difficulty, as an enlarged bronchial gland, pressing one of the bronchi. Here the free exit of the respired atmosphere being prevented, an accumulation of air takes place behind the narrowed point. Any impediment to the entrance or exit of the air into the lungs will produce irregular and forcible breathing, and throw a greater strain upon those parts especially which are in the vicinity of the obstacle. If, at the same time, the patient suffers an attack of asthma, bronchial catarrh, or whooping-cough, the violence of the cough materially aids in developing the dilatation. The degree of dilatation is greatly variable. Tubes which, in their natural state, are not larger than a crow-quill, may, especially in the lower and middle lobes, reach the size of the finger, while at various points, sacular dilatations may occur, which at first sight may appear as vomicæ, but which upon more careful inspection, prove to be dilated portions of the bronchial tubes. The tubes in this state are usually filled with a puriform fluid, upon the removal of which the lining membrane is seen to be reddened and softened, or perhaps ulcerated. This condition of the bronchial tubes may frequently be detected during life. The voice is hoarse, like a person in croup. The cough is also hoarse and brazen, while the breathing is difficult, and mucus rattling is heard in the middle or lower portion of the lung. The post-mortem appearances in cases of _foreign bodies_ in the bronchial tubes, may be readily anticipated and easily recognized. The Mediastinum. _Inflammation_ may arise in the anterior mediastinum, from fracture or caries of the sternum; and in the posterior, from injury, inflammation, caries, or necrosis of the vertebræ. This inflammation may also result in the formation of an _Abscess_; or, ulceration and perforation of the œsophagus, or inflammation of the lymphatic glands may lead to the same results. These abscesses may reach large size, resulting in displacement of the heart, and may rupture into the pleural cavity, the trachea or œsophagus. _Tumors_ of various kinds, may also develop within this space, including the several forms of _cancerous growths_. The latter will frequently have their origin in the bronchial or lymphatic glands, or, perhaps, in the remnant of the thymus gland.