PNEUMONIA. 4! 
CHAPTER II. 
PNEUMONIA. 
Tue lungs are rightly termed “ spongy organs,” for they abound in cavities, 
and have but comparatively little weight. In fact, a healthy lung will float on 
water; and it has been estimated that the number of air-cells in the lungs of a 
man is not less than six hundred millions. 
Pneumonia is an inflammation of the lung substance, characterized by pecu- 
liar changes which enable it to be divided into three distinct stages. 
In the first, that portion of the lung affected is engorged with blood and con- 
gested, and there commences an exudation, something like clotted blood, into 
the air-cells and little tubes. 
In the second, these air-cells and tubes are quickly filled with this exudation, 
which is now abundant; and by the means of it that part of the lung inflamed 
is rendered solid and impervious to air. Physicians term this the stage of “red 
hepatization,” because of the color of the lung involved, and its resemblance to 
liver. 
In the third stage, termed resolution, the coagulable exudation dissolves, as 
it were, and is absorbed. When this change goes on favorably and is com- 
pleted, the lung is restored to its natural condition; but if the resolving process 
is interfered with, or does not take place, the affected lung-substance may 
undergo a purulent change, as when abscesses form, which result in its destruc- 
tion or death of the sufferer. Another possible accident is gangrenous degenera- 
tion or gangrene of the lungs. And still another is chronic pneumonia, in which 
there eventually takes place hypertrophy of certain tissues of the lungs. But 
none of these changes often occur in dogs; and with them the rule is that 
either recovery or death speedily results. 
Pneumonia may be limited to a small area, but soon, if not at first, from one- 
third to one-half of a lung is generally included in the inflammation. Less 
often an entire lung is involved; and much more rarely are portions of both 
lungs inflamed during the same attack. Generally, also, there is a decided ten- 
dency for the inflammation to extend. That is, although only one-third or one- 
half of a lung be first affected, the remaining portion of it is quite liable to 
become inflamed and experience the same changes as the part first invaded. 
To ascribe this disease to accidental causes, especially to a sudden chill in 
consequence of wet and cold, is traditionary ; consequently when the theory was 
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