EMPHYSEMA. 319 



limited to childhood, for only at that period of life does the 

 interstitial tissue form any considerable bulk of the organ. 



Hypertrophic emphysema is the form of emphysema most 

 commonly met with. In this form the lungs are actually increased 

 in bulk. The emphysematous dilatation of air cells is chiefly 

 found in the thin and unsupported parts of the organs, i.e., along 

 the anterior edges, around the sharp basal margins and near 

 the roots. The accompanying increase in bulk is accommodated 

 in part by invasion of the spare pleural space and in part by 

 the inspiratory position assumed by the thorax, together with 

 exaggeration of the dorsal curve of the spine. The spare pleural 

 spaces which can accommodate the enlarged lungs are the 

 phrenico-costal and the pleuro-pericardial portions of the pleural 

 sinuses. The phrenico-costal sinuses, which lie below the lower 

 edges of the lungs between the diaphragm and the chest walls, 

 are of considerable potential capacity, and attain a vertical 

 measurement of nearly four inches in the axillary regions. In 

 this position the lower border of the lung normally reaches to 

 the. eighth rib whilst the pleural reflexion corresponds to the 

 tenth rib or intercostal space. The pleuro-pericardial sinus is a 

 part of the left pleural sac which passes further forwards over 

 the heart than the corresponding lung does. It is easy to see how 

 the emphysematous lungs by encroaching on these sinuses cause 

 the upper limits of the hepatic and splenic dulness to be depressed 

 and may diminish or obliterate the area of cardiac dulness. 

 When the chest wall assumes an inspiratory position, in addition 

 to the increase in its diameters which gives rise to the so-called 

 barrel outline, there is a certain amount of gliding upwards of 

 the ribs beneath the skin so that the surface relations become 

 altered. The nipple may lie on the fifth instead of the fourth 

 rib and the cardiac impulse may appear in the sixth space. In 

 emphysema, this altered relation tends to be permanent, and 

 must be taken into account in estimating cardiac enlargement 

 and displacement. 



The destruction of alveolar septa which takes place in 

 emphysema considerably reduces the capillary area of the 



