718 THE RESPIRATORY TRACT. 



deries and in brass f ounderies, all show differences in color. The 

 pigment in the alveolar epithelia consists of minute black gran- 

 ules, and in the interlobular connective tissue it is present in 

 clusters. The bronchial lymph-ganglia are found jet-black in 

 persons with pigmented lungs, owing to the coloring matter 

 carried into the lymph-tissue from without. There is no founda- 

 tion, however, for the assertion that such an accumulation of 

 pigment causes serious diseases of the lungs, although it is 

 unquestionably a morbid condition. 



Emphysema is another morbid condition of the lungs of very 

 frequent occurrence. It consists in a mere dilatation of the alve- 

 oli, vesicular emphysema, or in a rupture of the septa and a 

 union of a number of alveoli lobular emphysema. It is caused 

 by forced inspiration and impeded expiration due to obstructions 

 of the air-passages, and their consequent dilatation by coughing, 

 in chronic laryngitis and bronchitis. Emphysema is found most 

 commonly along the anterior borders of the lungs. The over- 

 distention of the alveoli gradually leads to a loss of the elasticity 

 of the wall, and to a permanent dilatation of the alveoli. In 

 higher degrees there is a rupture of the distended septa without 

 haemorrhage, as the blood-vessels become obliterated before the 

 rupture takes place. Higher degrees of emphysema invariably 

 lead to hypertrophy of the heart, interstitial hepatitis, and 

 catarrh al or croupous nephritis, with general anasarca and fatal 

 termination. (See Fig. 320.) 



Inflammation of the lung (pneumonia) appears in two principal 

 varieties : croupous or fibrinous or lobar pneumonia, and catarrhal 

 or lobular pneumonia. The former involves, nearly uniformly and 

 in a comparatively short time, large portions of the lung-tissue, 

 whole lobes, or the entire lung ; the latter is located in single 

 lobules or in groups of lobules, and runs a more protracted 

 course. Children under five years of age are very rarely affected 

 with croupous pneumonia, but the catarrhal form is of frequent 

 occurrence in early life. Under the microscope the distinguish- 

 ing features are as follows : In croupous pneumonia the intersti- 

 tial connective tissue is not markedly changed or increased ; the 

 alveoli are slightly distended and filled with an interlacing coag- 

 ulum of fibrine, in which are entangled red blood-corpuscles, 

 inflammatory corpuscles, and detached alveolar epithelia in vary- 

 ing numbers. In catarrhal pneumonia the interstitial tissue is 

 increased and crowded with inflammatory corpuscles ; the alveoli 

 are distended by a finely granular, albuminous exudate, contain- 



