184 Report on the Pathological Anatomy of Pleuro-pneumonia. 
the line of demarcation is often very distinct between this clear 
exudation and perfect consolidation, there are so many degrees 
of the former, that it seems capable of passing into more dense 
forms of induration, and it is difficult to find any characteristic 
which would serve to distinguish all grades of this change from 
that about to be described, but, as will be seen, the two must be 
kept quite distinct. The more dense the affected parts the more 
perfectly marked is the exudation into the interlobular spaces, 
and therefore the more perfect is the development of the 
marbling. 
The microscopic examination of this translucent spongy kind 
of condensation of the lung tissue shows that, in the earlier 
stages, there is but little change in the characters of the 
tissue-elements. The cavities of the air-cells are filled with a 
material which is obviously recently clotted serous exudation. 
It consists of delicate threads of fibrin and a few granular cor- 
puscles. The fibrin threads are variously knotted and granular, 
and appear to radiate from the corpuscles. The very same 
kind of material is found to fill the lymph-passages of the 
interlobular spaces, and the small bronchioles contain some 
similar fibrinous fluid. The network of capillary vessels around 
the air vesicles is quite empty of blood, and therefore cannot be 
well seen in this stage of the disease. The number of cell 
elements differs very much in different cases. They are chiefly, 
to all appearance, ordinary white blood corpuscles. In the 
cases where the exudation is more abundant, however, there is 
also a number of cells, which are much larger and more granular, 
and in the midst of them a very distinct nucleus is obvious. 
The more solid and brawny the tissue, the more numerous these 
large coarsely granular cells are found to be, and the more 
thick-set is the network formed of the granular threads of fibrin. 
In the denser forms of disease the epithelium, lining the alveoli, 
appears to be changed. The cells are granular and thick, and 
their nucleus becomes prominent, so that the cells, which in the 
normal lung are so very difficult to see, become so obvious as 
to attract the attention of the most thoughtless observer.^ 
Opaque Consolidation. — The kind of induration next to be 
noticed may, as I have already said, closely resemble the result 
of a long-continued state of the clear exudation just described, 
which seems gradually to pass through a series of changes, each 
being more dense than the preceding, until a condition is arrived 
at which deserves the name of perfect consolidation. But this is 
not to be confounded with what I call opaque consolidation, 
from which it differs in its mode of origin, its development 
not being preceded by the last-described infiltration. It is 
invariably less resilient, and is more granular in appearance. 
