PRIZE ESSAY . — PLEURO-PNEUMONIA AMONG CATTLE. 517 
the forwarding of cattle from one place to another are now ob- 
viated by the facilities afforded by railways. 
If we take a general survey of the causes just brought forward, 
we shall find that they almost collectively lead us to the conclu- 
sion that the manner in which cattle are met with, congregated 
together at fairs, markets, or passed from place to place, favours, if 
not the production, yet in a most remarkable manner the dissemi- 
nation, of the disease. 
It. is true that we might, at first sight, ascribe the frequent oc- 
currence of the disease in cattle so circumstanced to infection ; but 
we must bear in mind that they have all been placed in the same 
conditions, and that there can be no more reason that one should 
escape the effects produced by such conditions than another. We 
must, however, give some restriction to the last expression, be- 
cause it is probable that a particular animal, by virtue of its pecu- 
liar constitution, as well as its general health when brought 
amongst the stock, would be more liable to become affected by the 
conditions beforementioned than the others; and, moreover, we can 
conceive that an animal so disposed should take up the disease, 
and afterwards communicate it to others. But, quitting the subject 
which bears on the dissemination of the disease amongst drifted 
cattle, we shall next take into consideration the manner in which 
we have observed it to break out most frequently in private esta- 
blishments ; and a reference to our cases in general, but to Cases 
14, 15, 18, 22, and 29, in particular, will, we think, satisfactorily 
shew that it is chiefly due to the introduction of drifted cattle to 
home-stock ; and the fact of the latter, which were previously in 
good health, becoming affected after being brought into communi- 
cation with the drifted or diseased cattle, establishes in our mind 
the proof that the disease is infectious. As regards the “ mode 
of infection” itself, it is difficult to say whether immediate contact 
be necessary or not : but we can readily conceive the air itself to 
be a medium by which the disease may be communicated from 
one animal to another. 
There is another point of view under which it would be well to 
consider this question — how far premises previously occupied by 
diseased animals, but from which they had been removed, may 
communicate the disorder to fresh comers? But this question can 
hardly be discussed apart, for it involves another consideration, 
that of the healthiness of the locality itself ; and it may not un- 
frequently have happened that instances of disease successively 
occurring in different animals in the same locality may have been 
with less correctness ascribed to the influence of infection than 
to the unhealthiness of the former : the losses which Mr. Fletcher 
experienced might with as much justice be referred to the general 
