PRIZE ESSAY: — PLEURO-PNEUMONIA AMONG CATTLE. 411 
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 intervening 
cellular tissue, diffused through it in areolar webs, and separating 
the pulmonary tissue into lobules : hence it may be termed in- 
terlobular areolar tissue. It will simplify the study of the effects 
of this disease to consider the latter first; and if we refer to fig. 6, 
which represents a piece of healthy lung, we shall find the in- 
terlobular 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, glistening, and semi- 
transparent character. If we pass to fig. (2 d ), we shall find this 
offering a white or yellow colour, and assuming a firmer structure, 
interspersed 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. ] (c), or fig. 4 (c), we find this interlobular cellular tissue offer- 
ing such a degree of thickness, as to give it the appearance of en- 
tering in a large proportion into the structure of the lung itself, 
and its continuity with the sub-pleural 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, these 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 
latter. As the middle lobe of the right and the anterior part of 
the posterior lobe of the left lung are the parts which the inflam- 
mation seems usually to affect first, it would be advisable, when 
examining the chest of an animal, to direct our attention to the 
middle part of the back in the region corresponding to the angles 
of the ribs. 
In the last case described (15), a morbid product was found not 
only in the anterior lobe of the lung affected with the disease, but 
