584 
REVIEW — ON THE EPIZOOTIC IN CATTLE. 
that a similar disease had for many years been known in Switzer- 
land and France, yet the first accounts we have of pleuro-pneu- 
monia in Britain date no further back than 1841, and then it came 
to us from Ireland, along with the Irish droves transported across 
the channel, whose footsteps it subsequently might be traced to 
have observed in its progress through our own country, as it spread 
devastation among our herds, and ruined many a breeder and 
holder of stock. 
“ The causes of the disease, both immediate and remote, are sub- 
jects full of interest and importance ; and a knowledge of them not 
only aids in the prevention of disease, but also leads the practitioner 
to form a more correct prognosis, and to pursue the most approved 
course of treatment. It is, however, unfortunate that the causes of 
pleuro-pneumonia have not as yet been satisfactorily ascertained. 
No department of the history of the disease is less understood, or 
more involved in doubt and obscurity. But in this respect pleuro- 
pneumonia is not peculiar : it is but one of an extensive class 
which embraces most epidemic and epizootic diseases. And if the 
causes which produce influenza, fevers, and cholera, were clearly 
explained, those which produce pleuro-pneumonia would, in ail 
probability, be easy of solution. 
“ Viewing the wide-spread and similar effects of pleuro-pneumonia, 
we may surmise that they are referrible to some common cause. 
And although much difference of opinion exists upon this subject, 
it cannot be denied that CONTAGION is a most active cause in the 
diffusion of the disease. Indeed, a due consideration of the history 
and spread of pleuro-pneumonia over all parts of the land will be 
sufficient to shew that, in certain stages of the disease, it possesses 
the power of infecting animals apparently in a sound and healthy 
condition, and otherwise unexposed to the action of any exciting 
cause. The peculiarity of the progress of pleuro-pneumonia, from 
the time that it first appeared in England, is of itself no small 
evidence of its contagious nature. Its slow and gradual progress 
is eminently characteristic of diffusion by contagion ; and not only 
were the earlier cases which occurred in this island distinctly 
proved to have arisen from contact with the Irish droves, but also 
subsequent cases, even up to the present day, shew numerous ex- 
amples in which contagion is clearly and unequivocally traceable.” 
Mr. Dun holds that, “ although contagion may not be the sole 
exciting cause of all cases of pleuro-pneumonia, it is undoubtedly 
the principal and most fertile cause.” 
“Although contagion is admitted as producing many cases of 
