HYPERJ2MIA OF THE LUNG. 137 



take place in the alveoli in all cases of severe hyperaemia. Here, too, 

 the walls swell up, become more moist and succulent, but the secretion, 

 or, more properly, the transudation, which is poured into the cells differs 

 from the bronchial secretion, being liquid and serous. If we bear in 

 mind that there are but few mucous follicles even in the finer bronchi, 

 and none at all in the air-cells, and that the structureless cell-wall is cov- 

 ered merely by imperfect pavement epithelium, it must be evident that 

 the secretion from the vesicles, which have no mucous membrane proper, 

 must be very different from bronchial mucus. While, in other organs, 

 the term oedema is applied to an effusion of serum into the interstitial 

 tissues, the term oedema of the lung is only used in cases where such 

 infiltration is combined with an effusion upon the free surface of the 

 lung, i. e. y into the pulmonary vesicles. 



(Edema of the lung, however, is not, in all cases, a consequence of 

 hyperaemia, or of increased pressure of the contents of the capillaries upon 

 their walls, but, as in other organs, serum filters out of the pulmonary 

 capillaries into the tissue and into the vesicles, under slight pressure, 

 whenever the serum of the blood has but very little albumen in solution, 

 or whenever a dropsical crasis has developed. We shah 1 consider this 

 subject more fully in treating of Bright's disease. 



If oedema arise from a hypostatic hyperaemia, it is called hypostatic 

 cedema. As we have learned, however, there is a double reason for the 

 vascular engorgement in hypostatic hyperaemia, and hence it is easy to 

 understand that in this form the capillaries become extremely overfilled, 

 and that their walls undergo an excessive pressure. In this form of 

 hyperaemia it is not merely a transudation of a solution of dilute albu- 

 men which takes place, but all portions of the serum of the blood, even 

 the fibrin, pass through the now porous wall of the vessels, and we call 

 this condition hypostatic pneumonia, a process which takes place simply 

 from stagnation of the blood, and has nothing in common with inflam- 

 mation proper. 



ANATOMICAL APPEARANCES. When the hyperaemia is moderate, 

 the lung is bloated, dark red in color, and its vessels are filled to bursting. 

 The tissue is succulent, relaxed, crackles but little, blood flowing freely 

 over the cut surface ; a bloody, foamy liquid is contained in the bron- 

 chi. When of longer duration and greater intensity, the parenchyma 

 looks dark, bluish red or blackish red. The interstitial tissue and the 

 alveolar walls are so much swollen that the condensed parenchyma 

 scarcely gives any indication of its cellular structure. The lung, thus 

 solidified, presents a certain similarity of appearance to the tissue of the 

 spleen, and is therefore said to be splenified. 



If cedema have developed in the lung, it seems swollen, does not 

 collapse when we open the chest, and is tense to the touch. If recent, 





