188 Report on the Pathological Anatomy of Pleuro-pneumonia. 
and filled every available corner of the air vesicles. The larger 
blood-vessels are also filled with plugs of clotted blood, which 
adhere to their walls. 
This form of black consolidation, which obviously is the con- 
dition known as haemorrhagic infarction, is never found alone ; 
it is always associated with, and preceded by, the other lesions, 
which seem to be of much longer standing. 
Like the other morbid changes, this appears to pass through a 
series of stages, which depend on the changes taking place in 
the effused blood and in the nutrition of the tissue. The first 
step must occur with great rapidity, for one never meets with 
any initial state of hyperaemia. Where the lesion has lasted 
for some time, the tissue is found to have lost its elastic tough- 
ness, and become hard, dry, and friable, and at the same time 
its colour has faded to a dull brown. The friability of the part 
may increase, so as to form a dry crumbling mass, which ultimately 
undergoes caseous degeneration. In other cases the death of the 
tissue occurs more suddenly, and the part becomes gangrenous. 
The dead tissue may be surrounded with a kind of fibrous case, 
so as to remain shut off from the neighbouring parts. Some- 
times this completely separates, and remains in the chest as a 
cyst, containing a mass of cheesy degeneration. These cases only 
occur where the cure of disease has been attempted instead of 
the animal being slaughtered. 
To sum up the more important of the foregoing facts. 
1. The lung parenchyma is usually the seat of various forms 
of irregularly arranged exudation, which give it a mottled look. 
2. The interlobular spaces are always the seat of more or less 
exudation, which gives their sections the appearance of pale 
yellowish lines. 
3. These pale lines subdivide the mottled surface into irre- 
gular small fields, and thus give the effect which is deemed so 
characteristic — marbling. 
4. Three kinds of lesion must be distinguised in the lung. 
(a) A more or less fluid exudation, making the paren- 
chyma airless, though soft and translucent ;' this is 
diffused superficially, and wide-spread. 
(J) A dense, opaque consolidation, which is generally 
the central focus of disease, and is wedge-shaped 
and defined. 
(c) Black consolidation — haemorrhagic infarction. 
5. (a) or {!)) May pass into consolidation of a dense kind, and 
ultimately may form tissue of cicatricial hardness : 
6. (c) May produce gangrene, caseous degeneration, or fibri- 
nous crumbling. 
