Report on the Pathological Anatomy of Pleuro-pneumonia. 185 
In the earliest stages of the disease the two forms of lesion can 
be easily distinguished one from the other. 
This opaque condition is always more vascular than the clear 
exudation, but cannot be said to be much engorged, although 
here and there the blood-vessels are more or less distended with 
blood, so as to give the tissue a bright reddish-brown colour. 
This is the exception rather than the rule, for the usual colour of 
the section-surface is a pale brownish-red. The parenchyma 
is not at all translucent, the tissue being quite opaque as well 
as solid. The spaces between the lobules are densely filled with 
an opaque dry exudation, which in places can be turned out of 
the lymph-vessels, as distinct casts of their internal conformation. 
The air vesicles are filled with a somewhat similar material, 
which, under the microscope, proves to be composed of great 
numbers of cells, entangled in a dense felt-work of delicate 
granular fibrin threads, united into a dense solid mass. The 
swelling of the entire part is much greater than in the translu- 
cent form, and the spaces between the lobules are much more 
distended ; at the same time they retain their pale straw- 
colour, and form the striking system of markings seen in the 
" marbling." 
Every part of this true consolidation is hard, heavy, and 
resisting, but not so elastic as the parts which are translucent 
and soft. In a few instances the tissue has been found to be 
friable, apparently from a tendency to necrosis, caused by want 
of nutrition, the blood-vessels being pressed upon by the swell- 
ing. This is an exceptional case, however, for, as a general rule, 
the nutrition of the part is not at all interfered with, and the 
tissue not only retains its firmness, but continues to become 
more and more solid, until an almost cartilaginous consistence 
is attained. The bronchial arteries supply the nutrition, and 
are much enlarged. This induration is associated with a dis- 
tinct increase of the tissue elements, of the connective tissue 
septae between the lobules, and also of the tissue of the lobules 
themselves. In some cases, where the animal has been allowed 
to live a long time, the fibrous thickening of the interlobular 
spaces increases to such a degree, that the lobules are greatly 
encroached upon, and the vesicular tissue becomes so altered 
that the lung parenchyma can hardly be recognised. In this 
stage, which is now rarely met with, the animal being slaughtered 
when first the disease is recognised, the lung is nearly as dense 
as fibro-cartilage, creaking under the edge of the knife like 
gristle. Most of the smaller bronchi are obliterated, and even 
tubes which should normally admit the little finger have been 
found closed and impervious, their existence only being re- 
cognised by the cartilage of their wall remaining unaltered 
