22 CANINE MEDICINE AND SURGERY 



communicating with them gradually become filled 

 and finally distended with this exudate, the air in 

 them is expelled or absorbed by degrees, and the 

 affedted lung tissue becomes solid and heavy. If 

 the parts be now examined microscopically, the 

 dilated blood vessels will be found crowded with 

 their corpuscular contents, and the alveoli full of 

 cells, all blended together into a common mass 

 either by an amorphous, glutinous cement, or by 

 a delicate, fibrillated network. With the progress 

 of the disease the contents of the air vesicles 

 liquefy and acquire a purulent character. This 

 liquefied exudate is removed partly by expectora- 

 tion and partly by gradual absorption. Occasion- 

 ally, however, this breaking up of the exudate is 

 followed by a breaking down of the lung substance, 

 abscess formation, and gangrene. 



The progress of a case of pneumonia through its 

 various phases is quite gradual, but there are at 

 least three stages that are more or less well 

 marked. The first of these is the stage of en- 

 gorgement (congestion, hyperemia), the second that 

 of red hepatization, the third that of gray hepatiza- 

 tion. In the first stage the lung still contains air, 

 .though in diminished quantity; it is deeply con- 

 gested, exudes more moisture than is natural, is 

 increased in weight, and is more friable than nor- 

 mal lung tissue. This condition of the lung tissue 

 is difficult to distinguish from hypostatic conges- 

 tion, for which it must not be mistaken if found 

 on autopsy. In the .second stage the lung is con- 

 solidated; the cells have lost their air and the 

 cavities are filled with adherent masses of cells; 

 it is distended to its full size, and its constituent 

 lobules are distinctly mapped out upon the sur- 

 face. In this stage the lung will sink in water 



