PLEUROPNEUMONIA. 
821 
ments upon the subject of infection and contagion, it will be 
sufficient to interpret these expressions by the common term 
“ catching. 5 ' Is the lung disease of cattle an affection which 
a healthy bullock may catch from contact, either direct or in- 
direct, with the excretions, fluid or solid, of a diseased beast? 
A few years ago many practical men would have scouted the 
idea of such a result being possible ; and there are not wanting 
now men, both practical and theoretical, who assert that lung 
disease is not “ catching . 55 The supporters of either view seem 
to be only capable of appreciating the facts w hich bear upon 
their own convictions. Thus, on one side it is asserted that 
pleuropneumonia often arises in a herd which has been isolated 
for many weeks previously, and so placed that contact with 
diseased cattle could not have happened. Again, it is alleged 
that healthy animals placed with diseased ones do not become 
affected ; and further that, in many instances, only a few 7 of 
a herd are attacked, — the rest escaping the malady, although 
no precautions are taken to protect them. All these state- 
ments are quite accurate. Lung disease has appeared over 
and over again among animals which could not have been in 
direct contact with diseased beasts at any time during three 
or four months previously to the outbreak. In many in- 
stances of recent date lung disease has suddenly appeared 
among dairy cow t s several months subsequently to the intro- 
duction of fresh stock, arid the animals last purchased are not 
always the first to be attacked. This fact is w T ell known to 
owners of dairy stock, and, in some degree, accounts for their 
scepticism in reference to the infectiousness of the disease. 
Not long ago lung disease was detected in the North of Ireland 
among some calves about ten weeks old, bred on the pre- 
mises, and at some considerable distance from other stock. 
No other cases of disease existed on the estate or in the 
neighbourhood, and the event was classed among many 
similar instances in which the origin of the disease was unac- 
countable. It is also true that healthy cattle have been 
placed in the same shed or field with diseased animals and 
have not become affected ; and every experienced stock- 
owner is aw T are of instances of one or two animals in a herd 
being attacked fatally, it may be, while the others have 
entirely escaped. 
On the other side of the argument the facts are very defi- 
nite in character. In numberless cases the introduction of a 
diseased animal has been followed by the extension of the 
malady to all or the greater part of the herd. To give a 
fair idea of the kind of evidence which may be advanced 
in favour of the contagion theory, the following facts, 
