THOUGHTS ON BROKEN WIND. 
13 
the contrary, they vary most remarkably, from being dependent 
on a variety of circumstances, some of which are capable of 
explanation, while others baffle inquiry. Medical treatment, 
dieting, exercise, and change of temperature and air, produce 
the most marked effects on it; and sometimes, without any 
assignable reason, the most surprising changes for the better 
or worse take place. 
We will now compare the state of things in the living animal 
with what is presented to us after death. Firstly, I will detail 
the ordinary appearances; secondly, the varieties. 
Firstly.—The lungs are generally found to be in an emphy¬ 
sematous state; which, be it the cause or effect of the disease, 
produces a difficulty (more or less, according to the degree in 
which they are so affected) in the expulsion of the inspired air. 
Emphysema is of two kinds,—vesicular, or pulmonary and 
interlobular. The first of these has been most frequently 
noticed, and consists either simply in the dilatation of the 
minute bronchi and air-cells, or in the rupture of the parietes of 
several contiguous cells, and their consequent dilatation into 
one. This may occur only partially or through the entire 
structure of the lung, and is evidenced by the raised tubercular 
feel on the substance of the lung, and by its semi-transparent 
colour at these places. The other kind of emphysema, and 
which has not been so frequently observed, is the interlobular; 
which consists in the infiltration of air in consequence of the 
rupture of the membranous partitions between the lobules of the 
air-cells into the cellular tissue interposed between the lobules, 
and connecting them together. . Another appearance is some¬ 
times found on the lungs of horses which must not be con¬ 
founded with the two real forms, viz. sub-pleural vesicles, or 
air confined beneath the pleurae. This has often been noticed 
to exist in animals that have died or which have been slaugh¬ 
tered, though apparently quite free from any affection of the 
lungs. The nature of this emphysematious sac or bladder of 
air is different from the two true forms first named; and 
whether it consist simply in the bursting of an air-cell, or 
whether the air be secreted from the blood, is not very clear. 
In pulmonary emphysema the contained air, by the pressure of 
the finger, is with much difficulty made to leave its place; whereas, 
in the sub-pleural variety, it readily traverses the surface of the 
lung. In interlobular emphysema the partitions between the 
lobules are strongly defined and transparent, and the air may 
be made to traverse through the cellular membrane between the 
lobules. The pulmonary variety, on account of the thinness of 
substance along the edges of the lobes, is usually very plainly 
seen at those parts. When these vesicles are cut into, their 
