Pleiiro-Pncumonia anioiif/st Cattle. 
353 
of coagulated lymph adliering to the outer surface of the pleura, 
inasmuch as it is firm, indurated, and more or less beset with 
cells. In that respect it closely resembles the interlobular 
cellular tissue, and ought to be considered in association with the 
diseased state of the lung; but that it may be partly the means of 
communicating the inflammation of the pleura to the lung is a 
consideration not to be overlooked. 
The changes which occur in the parenchyma of the lung in 
this disease may be considered in reference to two tissues, the one 
the vesicular or proper structure of the lung — the other the in- 
tervening cellular tissue, diffused through it in areolar webs, and 
separating the pulmonary tissue into lobules ; hence it may be 
termed interlobular areolar tissue. It will simplify the study of 
the effects of this disease to consider the latter first, and if we 
refer to fig. G, which represents a piece of healthy lung, we shall 
find the interlobular tissue (c) but indistinctly marked ; but if we 
pass to fig. 5, which is a drawing of a piece of lung affected with 
emphysema, we may perceive that this interlobular cellular tissue 
is dilated by air (b and c), but still retaining its areolar, glisten- 
ing, and semi-transparent character. If we pass to fig. 2 (c?), we 
shall find this offering a white or yellow colour, and assuming a 
firmer structure, interspered with small cavities : that interlobular 
tissue, however, is seated amidst nearly healthy lung ; but in the 
same drawing we may observe at letter (a) the pulmonary tissue 
in apparently the first stage of inflammation, and in that part 
the interlobular cellular tissue (e) presents a degree of thickness 
much greater than what it did in the healthy portion. But if 
we next proceed to fig. 1 (c), or fig. 4 (c), we find this interlo- 
bular cellular tissue offering such a degree of thickness, as to 
give it the appearance of entering in a large proportion into the 
structure of the lung itself, and its continuity with the subpleural 
cellular tissue is such as to warrant the conclusion that they are 
identical in character. 
Whatever may be the form of the pulmonary cells and their 
relative arrangement, it is quite evident that in that stage of 
inflammation called hepatization, those cells become obliterated. 
This obliteration is due, in our opinion, to a change which has 
taken place in the walls of those cells which have become thick- 
ened, through an addition of organic matter, in the same manner 
as the inter-lobular cellular tissue had become increased in 
volume. 
A question has been mooted whether the tissue of the lung 
swells in inflammation, seeing that its volume is limited to the 
capacity of the thorax, but the swelling takes place inwards, 
i. e. the walls of the cells, by increasing in thickness, obliterate the 
