1C8 DISEASES OF THE PARENCHYMA OF THE LUNG. 



curious that in old persons and in cachectic individuals the mode of extern 

 sion is usually different, as here the upper lobes are generally the firs! 

 to be attacked, the lower not becoming involved until a later period of 

 the disease. We distinguish three anatomical stages in pneumonia: 

 1st, the stage of engorgement with blood (engouement] ; 2d, the stage 

 of hepatization ; 3d, the stage of purulent infiltration. 



In the first stage the pulmonary parenchyma is dark red, often red- 

 dish brown. It is heavier and firmer, has lost its elasticity, and pits upon 

 pressure. Upon section, the inflamed portion of the lung does not 

 crackle much, and a brownish or reddish liquid, of a strikingly viscid 

 and tenacious nature, bathes the surface of the cut. 



In the second stage, the air has disappeared from the air-vesicles, 

 and the latter are filled by small, firm plugs of coagulated fibrin, to 

 which an admixture of blood imparts a reddish color. A similar exuda- 

 tion has taken place in the extremities of the bronchi. The lung has 

 now become remarkably heavy, sinks in water, does not crackle, is firm 

 to the touch, but is very tender and friable. The appearance of its cut 

 surface is granulated, especially when viewed by oblique light, and this 

 is most distinct where the air-vesicles are large; less so in children, 

 where they are small. The granules (which are merely the fibrinous 

 plugs so often mentioned) can no longer be extracted from the lung by 

 scraping with the scalpel, but adhere firmly to the walls of the air-cells. 

 The granulated aspect of the cut-surface, the rigidity, the friability, the 

 redness of the condensed lung, impart to it a considerable resemblance 

 to liver, and thus the generally-adopted name of red hepatization has 

 arisen. 7 Sometimes, owing to spots of lighter color, and to deposits here 

 and there of the black pigment which is secreted in the lung, together 

 with the whiteness of the interior of the bisected bronchi and vessels, 

 the section, instead of a uniform red, presents a variegated, " marbled," 

 granite-like appearance. Afterward the redness fades more and more, 

 either from cessation of the hyperaemia, or from disintegration of the 

 haematin. The lung assumes a gray or yellowish appearance, while the 

 texture continues in other respects the same, the pulmonary substance 

 remaining rigid and granular (yellow hepatization). Besides the amor 

 phous fibrin which fills the air-vesicles, the microscope reveals a very 

 active formation of new cells, which probably spring from the epithe- 

 lium of the vesicular walls. Should resolution set in, in the stage of 

 hepatization, the fibrin and the young cells entangled in it undergo fatty 

 metamorphosis and disintegration. An albuminous serum transudes 

 from the walls of the vesicles; their contents become liquefied, con- 

 verted into an emulsion, and finally are eliminated, partially by absorp- 

 tion, partially by expectoration. There is a slight deviation from the 

 above when the pneumonic exudation is less fibrinous and less coagu- 



