PNEUMONIA. 489 
be given to it. It would be necessary to select at random a number of 
roaring sires and dams, and compare their stock with that of an equal pro- 
portion of sound animals, which would be a Herculean task, beyond the 
power of any private individual. Nothing short of this could possibly 
settle the dispute; but, as far as opinion goes, it may be assumed that 
there are strong authorities against the hereditary nature of the diseases 
which produce roaring. That it is often the result of ordinary inflam- 
mation, which in itself can scarcely be considered hereditary, is plain 
enougb.; and that it is also produced by mismanagement in tight-reining 
is also admitted, which latter kind can scarcely be supposed to be handed 
down from sire to son; but that it is safer, when practicable, to avoid 
parents with any disease whatever, is patent to all. 
PNEUMONIA AND CONGESTION OF THE LUNGS. 
THE THEORETICAL DEFINITION OF PNEUMONIA is that it consists of inflam- 
mation of the parenchyma of the lungs, independently both of the mucous 
lining to the air passages, and of the serous covering of the whole mass. 
On turning to page 423, it will be seen that the mucous membrane ceases 
abruptly at the terminations of the bronchial subdivisions, and conse- 
quently that the air cells are not lined with a continuation from it. Hence 
there is an extensive cellulo-tibrous area, which may be the subject of 
inflammation, without implicating the mucous surface. Until within the 
last fifteen or twenty years, it was commonly supposed that the air cells 
were all lined by mucous membrane, and that the parenchyma was con- 
fined to an almost infinitesimally thin structure, filling up its interstices ; 
but the microscope has revealed the true structure of the lungs, and has 
shown that there is a well-founded distinction between bronchitis and 
pneumonia, upon the ground of anatomy, as well as observation. Still, it 
cannot be denied that the one seldom exists to any great extent, or for 
any long period, without involving the adjacent tissue; and broncho- 
pneumonia as well as pleuro-pneumonia are as common as the pure 
disease. 
PNEUMONIA, OR PERIPNEUMONY, must be examined, with a view, first, to 
its intensity, whether acute or swb-acute ; and secondly, as to its effects, 
which may be of little consequence, or they may be so serious as to com- 
pletely destroy the subsequent usefulness of the patient. It is not, there- 
. fore, alone necessary to provide against death by the treatment adopted, 
but due care must also be taken that the tissue of the lungs is not dis- 
organised by a deposition of lymph, or of matter, so as to lead, in the one 
case, to a consolidation of the air cells, and, in the other, to the formation 
of a large abscess, and consequent destruction of substance. The former 
is Avery common sequel of pneumonia; and probably there are few attacks 
of it without being followed by a greater or less degree of hepatization, by 
which term the deposit of lymph is known from its causing the lungs to 
assume the texture of liver (jap). In very severe cases, gangrene of the 
lungs is induced ; but as death almost always speedily follows this con- 
dition, it is not necessary to consider it, excepting as bearing upon the 
fatal result. 
The cause of pneumonia may be over-exertion, as in the hurting-field, 
especially in an unprepared horse ; or it may come on as a primary disease 
after ex osure to cold ; or it may follow upon bronchitis when neglected 
and ally wed to run on without check. In the two first cases it appears to 
be projiuced by the great congestion of blood which takes place in the 
