162 DISEASES OF THE PARENCHYMA OF THE LUNG. 



come incapsulated, and its contents may thicken into a cheesy or calca- 

 reous mass. 



Gangrene of the lung, as a result of haemorrhagic infarction, will be 

 described in Chapter XII. 



In explaining the pathogeny of metastatic infarction, we have already 

 alluded to the small volume, the cuneiform shape, and superficial situa- 

 tion which it generally assumes. In color, consistence, and friability, 

 metastatic infarctions are entirely similar to those which arise from dis- 

 ease of the heart. The microscope also gives the same appearances. 



When metastatic infarction terminates in metastatic pneumonia or 

 abscess, discoloration and disintegration generally commence in the 

 middle of the diseased part ; cavities form, filled with a yellow mass, 

 which consists of debris of the pulmonary substance, and of molecular 

 decay of the extravasated blood and fibrin, but which at first does not 

 contain any pus. Upon pouring water over its cut surface, we can see 

 the vestiges of the lung floating in the hollow. The disintegration 

 spreads gradually until scarcely a trace is left of former thickening, 

 even at the periphery of the abscess. When situated immediately under 

 the pleura, yellow croupous deposits form upon the latter, which cause 

 the pleural sui faces to become adherent, and beneath it lies the infarc- 

 tion, " forming a rounded-nodular prominence like a furuncle " (RoJci- 

 tansky). 



SYMPTOMS AND COURSE. We shah 1 treat separately of the symp- 

 toms of haemorrhagic infarction arising from diseased heart, and of those 

 of metastatic infarction ; since the appearance of the two forms of dis- 

 ease, in spite of their anatomical identity, varies in many respects on 

 account of the difference in the diseases which cause them. 



Ik many cases of chronic disease of the heart, haemorrhagic infarction 

 sets in with such well-marked and unequivocal symptoms, that its exist- 

 ence can be demonstrated with perfect certainty. In other cases the 

 proof is difficult, or quite impossible. 



The characteristic symptoms, from which we can infer the formation 

 of one or more haemorrhagic infarctions in a case of disease of the heart, 

 are, a sudden dyspnoea, which may threaten suffocation, and a cough 

 with a peculiar sputum tinged with blood. In many instances there are 

 the signs of a circumscribed condensation of the lung, which are not un- 

 frequently followed by those of pneumonia or of pleurisy. It is manifest 

 that the stoppage of one or more branches of the pulmonary artery will 

 produce extreme dyspnoea. As the process of respiration can only be 

 carried on normally, when both the air in the vesicles and the blood in 

 the capillaries are properly renewed, the arrest, either of access of blood, 

 or of entrance of air into part of the lung, the obstruction, either of a 

 bronchus, or of an arterial branch, must have an equal and extremely 



