484 THE RESPIRATORY SYSTEM. 



there is usually a new formation of fibrous tissue, so that the lung be- 

 comes indurated, leathery, and dry, and collapses less readily than nor- 

 mal. This condition is often called brown induration of the lung. This 

 formation of fibrous tissue is analogous with that which occurs in other 

 organs, such as the kidney and liver in chronic congestion. Emigration 

 of leucocytes is not infrequently associated with diapedesis from the 

 dilated capillaries, and these, with the desquamated epithelium, may 

 accumulate in the air vesicles. 



In oedema of the lungs the vesicles contain a clear, sometimes foamy, 

 fluid, occasionally tinged with blood, usually mixed with exfoliated ves- 

 ical epithelium. The cedematous fluid may be present in the bronchi 

 and in the interstitial tissue of the lungs. (Edema is often associated 

 with hyperaemia, and like this may vary in different parts of the lung. 

 On the other hand, there may be extensive oedema without overfilled 

 blood-vessels; these in excessive oedema may indeed be nearly empty and 

 compressed. (Edema of the lungs may occur in general infections and 

 intoxications, or in association with local inflammatory processes. Fatal 

 oedema of the lungs may be associated with fat embolism. 



The studies of Welch ! show that with diminished force exerted by 

 the left side of the heart, the vigor of the right remaining unimpaired, 

 oedema of the lungs may follow. 2 



HEMORRHAGE AND INFARCTION. 

 HAEMORRHAGE. 



Haemorrhages into the lung tissue and air spaces of the lungs may 

 occur from trauma, from rupture of aneurism, in acute infectious dis- 

 eases and intoxications, in scurvy and haematophilia, in asphyxia from 

 brain lesions or other conditions, from tuberculous ulcerations involving 

 the blood-vessels. Multiple ecchyuioses may occur in fat embolism. 



Haemorrhage is of frequent occurrence in excessive hyperaemia of the 

 lungs, notably in connection with mitral stenosis and insufficiency. Un- 

 der these conditions the extravasation of blood may take place by diape- 

 desis or by rhexis. The accumulations of blood may be single or mul- 

 tiple, localized or diffuse, dense and firm, or when oedema is present, 

 soft and fluid in character. During the last hours of life, owing to eu- 

 feeblement of the heart, extravasation of blood may occur which sinks 

 to the posterior dependent portions of the lungs. 



INFARCTION. 



As a result of thrombosis or embolism of the pulmonary artery, dense 

 collections of extravasated blood may form, called hcemorrhagic infarc- 



1 Welch, Virchow's Arcliiv, Bd. Ixxii., p. 375. 



2 For a study of the disturbances of circulation in the lungs under various abnormal 

 conditions see Esser, Centralbl. f. ges. Med., January 26th, 1901, bibliography. 



