578 POPULAR LECTURE ON THE PREVAILING EPIZOOTIC 
cognise it only through the medium of its effects ; nevertheless, 
in this instance, satisfactory deductions can be drawn from ana- 
logical reasoning. There are many tangible forms of poison, 
which, no matter how taken into the system, when destructive to 
life, produce the same specific effects on certain parts. 
Arsenic, when applied even to the external surface, causes with 
fatal effect, inflammation and ulceration of the stomach. 
Tartar emetic, when injected into the veins, excites most vio- 
lent vomition, an effect precisely similar to that which takes place 
from its being administered internally. These facts clearly prove 
the extraordinary susceptibility of some parts to be acted upon by 
certain agents. With respect to epidemic and epizootic diseases, to 
use a chemical term, there are some parts of the frame which have 
a much greater affinity for the diseasing principle than others, the 
product resulting from their combination being the disease. This 
mode of explanation, although extremely figurative, is yet the 
most expressive that suggests itself to my mind. 
I have stated that the exciting cause of the disease appears 
to exist in some peculiarity of the atmosphere; but of what the 
peculiarity is, in a physical point of view, we cannot ascertain, 
being made aware of its existence only through the medium of 
its disastrous effects among our herds of cattle. In alluding to 
the seat of disease, I described the air tubes and cells of the 
lungs as being frequently completely plugged up with lymph, 
and also the cellules composing the framework of these organs. 
The disease, however, does not always confine itself to the lungs, 
but extends also to their covering, and the lining of the ribs. 
The animal gets what is commonly called pleurisy as an addi- 
tional complication to the affection of the lungs. The pleural mem- 
brane (i. e., the covering of the lungs and lining of the ribs) be- 
comes acutely inflamed, pours out lymph from its surface, and 
also a quantity of bloody serous fluid, which, accumulating with- 
in the chest, presses on the lungs, and eventually causes death by 
suffocation. 
Sometimes formations of pus (matter) take place in the previ- 
ously solidified structure of the lungs, the abscesses not very un- 
frequently breaking into the chest, or some of the divisions of the 
windpipe. But, generally, the animal dies long before any of the 
effused lymph becomes changed into matter. 
One of the most extraordinary features of the present distem- 
per is the little tendency the solidified lung has to the formation 
of abscess. In this respect, the disease is unlike ordinary inflam- 
mation of the lungs, in which, when any part of these organs be- 
comes solidified, formations of matter in their structure frequently 
become in a short time a cause of hectic. In the present distem- 
per the liver is frequently found enlarged — hardened to an extra- 
