s to
pleuropneumonia and which may therefore be confused with it in some of its
phases.

If we kill an animal affected with acute pleuropneumonia and examine the
cavity of the chest and lungs, the following appearances will be noted:

The thorax may contain more or less serum, which may be clear or clouded.
There may be firm adhesions of different parts of the lungs to the chest
wall, the extent of which depends on the stage and severity of the disease.
The diseased lobes are unusually large and exceedingly firm to the touch.
The weight of a single large lobe may reach 40 pounds. Usually only one
side is affected, often but a single lobe, and this most commonly the large
or principal lobe. The pleura may be covered with one or more layers of a
firm, elastic, grayish membrane, which varies in thickness and which
sometimes may be pulled away entirely. Sometimes it is absent. The pleura,
however, is opaque and apparently very much thickened. This is owing to the
diseased condition of the connective tissue beneath the pleura, as will be
explained later. When an affected lobe is cut through at right angles to
its long diameter, the cut surface presents a variety of interesting
changes. In the first place the spaces between the small subdivisions of
the lung (the lobules), which in the healthy lung are barely visible, are
distended with a yellowish-white, usually quite firm, substance, which is
coagulated fibrin. The cut surface thus appears divided into small fields
by yellowish-white bands of varying thickness running in various directions
through the lung tissue and beneath the pleura. (Pl. XXXI.) These bands may
appear honeycombed and the spaces filled with yellowish fluid (serum) or
they may be uniformly solid. It will also be noticed that the space
immediately outside of and around the artery, vein, and air tube is
similarly broadened by fibrinous deposits. Some authorities look upon these
bands as constituting the so-called "marbling" of pleuropneumonia.

In addition to these changes which have taken place in the connective
tissue between the lobules, the lung tissue itself may be markedly altered.
Certain areas of the cut surface may be very firm in texture and of a
brownish-red color. The cut surface is granular or roughened, not smooth to
the eye. Other areas equally firm may be more grayish yellow and still
others may be blackish. (Pl. XXXII.) Besides these areas which represent
solidified (hepatized) lung tissue