196 The Lungs 



The muscular tissue, which in the trachea lay only behind, in the small 

 bronchi completely encircles them, and may be traced even into the 

 divisions of the air-tube which are too small to possess any cartilage. 

 The columnar epithelium which lines the tubes is rarely expectorated, 

 even when bronchial catarrh is severe. 



Ultimately the small bronchial tubes lose both cartilage and muscle 

 and expand into air-cells, which are lined with flattened epithelium. 

 Between these cells are crevices (stomata) which open into an alveolar 

 lymph-space ; through them germs, particles of soot or grit, may 

 reach the lymphatic vessels. The group of air-cells into which an 

 ultimate bronchial tube expands is cone-shaped and is called a lobule. 

 The lobules are distinct, and are separated by a delicate fibrous tissue 

 which is connected with the sub-pleural coat. 



Emphysema (cv, in ; cfrvo-au, blow) is just that condition which 

 would be induced by inserting the nozzle of bellows into the trachea 

 and vigorously ' blowing into ' the lungs. Some of the air-cells burst, 

 and allow air to escape into the connective tissue of the lungs (extra- 

 vesicular or interlobular emphysema], whilst others are over-stretched, 

 and in some places many cells are blended into one large cell 

 (vesicular emphyse?)id], Interlobular emphysema is especially apt to 

 occur in the delicate chest of a child with severe whooping-cough. 

 When emphysema is imitated on the cadaver the anterior edges of 

 the lungs glide over the heart, and their bases depress the diaphragm, 

 liver, stomach, and spleen ; the ribs are raised, the upper ones notably 

 so, the chest becoming high and barrel-shaped, and the neck being 

 shortened by the elevation of the sternum, the first rib, and the clavicle. 

 And, if only the bones were soft enough, the expanding lungs would 

 make the spine bow forwards, rendering the subject round-shouldered. 



The chest of the emphysematous man is hyper-resonant, even to 

 the twelfth rib, and on opening \\.post mortem the lungs do not collapse, 

 for much of their elasticity has been destroyed in the vesicular dilata- 

 tion, and the tubes are plugged with bronchitic mucus. The border of 

 the lung generally has, moreover, a bubbly fringe, and if during life 

 some of the bubbles had burst pneumothorax would have resulted. 



The trombone-playe ', by his forcible blasts, over-stretches the air- 

 cells and becomes emphysematous. So does the man with chronic 

 cough, for emphysema is developed during expiration. But there is 

 an additional reason for the subject of chronic bronchitis being emphy- 

 sematous, for many of his small bronchial tubes become permanently 

 plugged, the lobules associated with them collapsing ; but at each inspi- 

 ratory act the chest must still be filled, so the adjacent lobules undergo 

 double expansion, for when a part of the lung is permanently thrown 

 out of working order the air-cells in the healthy neighbourhood struggle 

 to fill its place, and suffer in the act. The emphysema thus produced 

 is called vicarious ; it is likewise a constant accompaniment of chronic 

 pneumonia. 



