CROUPOUS PNEUMONIA. 160 



[able. The liepatized portion then is softer, its cut is smoother, and 

 without distinct granulation. This is most common in the secondary 

 pneumonia of typhus, and in that of old persons. When the pneu- 

 monia passes into the third stage, that of purulent infiltration, cell-for- 

 mation assumes prominence, while the fibrin undergoes disintegration 

 as in other cases. The granulated appearance is lost, the cut-surface is 

 of a pale gray, or grayish yellow. A reddish-gray matter bathes its 

 surface, and may be expressed in large quantities. The tissues are ex- 

 ceedingly tender, and are easily torn by the pressure of the finger. The 

 minuter structure of the lung, however, is unaltered ; the pulmonary 

 tissue itself is still intact. Here, too, therefore, complete recovery may 

 take place. The purulent contents may be ejected in part, and in part 

 may undergo fatty degeneration and become absorbed. 

 The rarer sequelae of pneumonia are . 



1. Formation of abscess. The purely croupous form of inflamma- 

 tion with which we have here to do essentially excludes the idea of a 

 destruction of the inflamed tissue. When abscesses form, the process 

 has more of a diphtheritic nature. The proper tissue of the lung be- 

 comes infiltrated, and sloughs from the pressure of the fibrinous infiltra,- 

 tion. In this way small cavities, filled with pus and debris of the pul- 

 monary substance, form in the lung, which itself is infiltrated with pus. 

 Sometimes they are solitary and sometimes they exist in great number. 

 These collections of pus may increase in size from continual melting 

 down of the tissues ; several of them may coalesce, so that finally a 

 huge abscess may occupy the greater part of the lung. These abscesses 

 either end fatally through ulcerous phthisis, or else, in rarer instances, 

 they open into the pleural sac. In other cases, a reactive interstitial 

 pneumonia is set up in the parts adjacent, by which the abscess is in- 

 capsulated in a firm cicatricial tissue, its inner wall becoming smooth. 

 Should a communication with the bronchi remain, its contents are evacu- 

 ated from time to time, but are replaced by fresh matter generated by 

 the interior surface. Should the cavity be closed, the pus may become 

 thickened, and be converted into a cheesy paste, or, after disappearance 

 of the organic substance, may change into a mortar-like or chalky con- 

 cretion, which lies imbedded in an indurated firm scar. 



2. Gangrene of the lung is a still rarer sequel to pneumonia. It ap- 

 pears only to occur when the supply of blood has been completely cut off 

 from the inflamed portion of the lung by the formation of large coagula in 

 the pulmonary arteries, and more especially when they form in the bron- 

 chial arteries, by whose means nutrition of the lung is carried on. The lung 

 may become gangrenous even in the stage of red hepatization. The exu- 

 dation then changes into a grayish ichorous liquid, and the pulmonary 

 tissue breaks down into a blackish pulp. (See Chapter XII.) 



