360 
Pleuro- Pneumonia amongst Cattle. 
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 bj the conditions 
before mentioned, than the others ; and moreover, we can con- 
ceive 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 drilled 
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 
show 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 
unhealthiness of the premises, as to the effects of infection. In 
some of the cases of disease which we have related, viz. 17, 20, 
21, &c., the origin could not be traced to the effects of infection; 
and that circumstance adds to the importance we should attach to 
the conditions in which isolated animals are placed as regards their 
liability to disease. 
To dwell longer on this head would expose us to repetition 
when we bring the next subject to be treated under considera- 
tion. 
Precautions against Infection. 
Without discussing the point, whether the disease was intro- 
duced into this country by foreign cattle — or whether any system 
of police could have prevented that introduction — we must now, 
as regards precautions, consider the disease as it is met with in 
