Report on the Pathological Anatomy of Pleuro-pneumonia. 183 
In every case there are to be seen different shades of this 
marbling, which correspond to different stages in the disease, or 
are quite distinct morbid processes. I think it will simplify the 
description of the morbid anatomy of the lung, and render the 
steps in the progress of the disease more easily understood, 
if these various forms of pathological change be considered 
separately. 
Clear Exudation. — The first which I shall mention may be 
called simply exudation, or the infiltration of the tissues with a 
clear material. This condition is generally found in the peri- 
phery of the diseased region, and forms a very complete case, 
enclosing the dense forms of consolidation to be described here- 
after. This can be particularly well seen where but a small 
nodule exists. Thus, in one case, where only three lobules were 
in an advanced state of disease, all the lobules lying in imme- 
diate apposition to them were in a condition of pale cedematous- 
like thickening. When a great extent of the lung is engaged, 
the boundary of this transparent exudation is irregular and badly 
defined ; but when a limited area only is affected, its margin 
is sharply marked, and corresponds to the lines separating the 
lobules. 
There seems to be no increase in the amount of blood in the 
I lung in this condition. On the contrary, the blood-vessels 
appear, for the most part, empty, and the tissue anaemic. The 
pink colour is replaced by a pale yellow, or dull buff, and at the 
same time the tissue gets a peculiar semi-translucent look. A 
I clear fluid escapes from the cut surface. This is often mixed 
i with a little frothy fluid, but as a rule the tissue seems quite 
{ airless, and does not crepitate. The interlobular spaces are filled 
' with a clear fluid, which widely distends the interstices of the 
delicate connective tissue. Except in the cases where the disease 
II is very limited, the part filled with clear exudation does not 
I appear to have any very definite shape, as it easily spreads beyond 
the limits of the broncho-vascular territories, passing from one 
; interlobular space to another. When the pleural inflammation is 
I very intense, some of the lung tissue situated immediately under 
' it is affected with this infiltration, but it seldom reaches to a 
i depth of more than an inch or so from the pleural surface. 
: This mode of extension of the exudation, under the inflamed 
«l pleura, is of great importance, as it causes destruction of a large 
i part of the lung, and seems to spread the disease with great 
■I rapidity over an extensive area of the organ, giving rise to 
those cases where nearly the entire lung is implicated. 
A great variety of intensity of this exudation exists. The tissue 
appears at first to be soft and spongy ; the air is then gradually 
diminished, and the part becomes brawny and tough. Although 
