344 
ON EPIZOOTIC DISEASES. 
ence, generally speaking — temperature — certain localities — 
the bad construction and contaminated air of the buildings — the 
nature and quality of the food — travelling by sea and land — and 
accidents of every kind. When these are the causes that, under 
certain circumstances, prevent the improvement and destroy the 
lives of our cattle, we say that the diseases are epizootic. Among 
these causes, one is of so frequent occurrence that it may be said 
to be constant, — humidity. It acts on the vegetable world, and 
on the animals which it supports. It deprives the vegetables of 
a portion of their nutritive principles, and often gives them a 
deleterious quality. The grass and the grain undergo a species 
of germination which interferes with their wholesomeness, and 
gives to the general produce a disposition to fermentation. 
This humidity of the air and of the food exercises a peculiarly 
fatal influence on animals whose temperament is weak and lym- 
phatic, as in the ruminants it generally is. Sheep are too often 
disposed to imbibe this fatal influence. If the summer is charac- 
terised by almost undeviating moisture, the cattle, and more 
especially the sheep, become the victims of dropsy. Resulting 
from this influence of external agency is another, the ravages of 
which are truly dreadful. The cattle cannot be long exposed to 
this deleterious influence without the principle of contagion being 
fearfully developed. It is connected with the typhus of cattle 
and the more acute diseases of other animals ; and, from this 
cause, many contagious typhous diseases have been known to per- 
vade the whole of Europe. 
Under these circumstances, medicine too often renders feeble as- 
sistance. The unknown nature of the disease surrounds the prac- 
titioner with a degree of obscurity, which the torch of experience 
alone can dissipate, and of which he cannot avail himself when 
he is first called to attend on his patients. His early essays can 
scarcely be said to be guided by any scientific principle, and he 
must have time to observe and to reflect before he can decidedly 
act. The contagion is assuming daily a more decisive character — 
it is approaching nearer and nearer — the infected surface is en- 
larging — the propriety of one or another treatment cannot at 
first be satisfactorily determined, and, too often, the real nature of 
the disease cannot be ascertained until after the loss of many a 
patient. 
Some epizootics commence their ravages in a great number of 
places at the same time ; others are at first observed in one locality 
alone, but they rapidly spread on every side until they cover an 
immense extent of country. Some pursue a regular march from 
one district to another; others, suddenly disappear in one region, 
to devastate a distant one ; and, in too many cases the malady 
