EASTERN COUNTIES VETERINARY MEDICAL ASSOCIATION. 785 
by entering into lengthy argument as to the year and manner of its 
introduction ; suffice it to say, that from that time down to the 
present, it has continued to decimate our herds, sometimes ravaging 
with greater virulence than at others, now spreading rapidly over 
the country, and again being little heard of; but whether existing 
much or little, always proving fatal in a large majority of cases. 
Pleuro-pneumonia is an epizootic disease, depending upon a 
peculiar animal morbific poison, which, entering the blood through 
the medium of the respiratory organ, is for a certain time incubated 
in the system, during which period it continues to increase more or 
less rapidly, thus varying the incubative stage, which may last from 
three to several weeks. The effect of the poison appears to be to 
cause an excess of w'ater in the blood, and having grown, if I may 
so term it, and produced such changes that it cannot longer be con¬ 
tained by the blood-vessels (they being incapable from some cause of 
long containing blood in an impure state, or having any of the con¬ 
stituents of the fluid in excess) it localises itself in the lungs; 
although why the effect of one poison should spend its force upon 
one particular organ of the body, and another leave it free to attack 
some distant one, is at present a mystery, and is likely to remain 
so until we can arrive at some means of becoming better acquainted 
with these blood-poisons. That the morbific matter often exists in 
our atmosphere is, I think, beyond doubt, else how should we be 
able to explain the cause of severe outbreaks of the malady; for it 
is clear that although it is both contagious and infectious, it does 
not spread from animal to animal, as is the case with cattle plague. 
That at certain times the atmosphere is loaded with poisonous vapour 
or miasma, which may be caused by the decomposition of animal 
or vegetable matter, destructive or injurious to animal or vegetable 
life, is a fact admitted by all scientific men; but little further 
than this can be said ; it is not always possible to tell when such 
a state of things exists, although it is often apparent; for who of us 
has failed to observe what is called commonly a blight spread over 
a certain tract of country, to find on the following day that vegeta¬ 
tion in some form has been considerably injured; if in spring, by 
the cutting off of the blossom or newly set fruit of apple, pear, or 
other trees; if later in the year, by the withering up of foliage. 
The morbific matter then, or a part of it, having left the blood¬ 
vessels, or rather a part of it having done so (as I think, after the 
localisation of the disease, it continues to develop so as to keep up 
the supply), may attack the whole or a portion of the lungs; an 
exudation of fluid containing a quantity of impure fibrin takes place 
into the interlobular and interstitial cellular tissue, the amount and 
extent of lung affected depending upon the quantity of morbific 
matter in the system, which, becoming partially solidified and com¬ 
pressing the lobules, prevents the free passage of air, and also from 
compression the blood-vessels become surcharged with dark blood; 
secondly, the vessels become ruptured, some light spots being 
accounted for by the breaking up of the constituents of the blood, 
at the same time effusion goes on into the cavity of the chest, in 
