586 
REVIEW— ON THE EPIZOOTIC IN CATTLE. 
difficult of detection ; nay, it is sometimes impossible to tell to 
what the disease is referrible, or upon what weak point the exciting 
cause has fixed itself. A source of perplexity results from the 
fact, that the disease appears under every variety of circumstance, 
and is fomented by apparently the most opposite causes. It 
appears in well and ill ventilated byres ; it may attack cattle well 
fed and in good condition, as well as those starved and neglected ; 
it may occur irrespective of the description of food, of cleanliness, 
and of the system of management. There is no season of the year 
that checks its course ; no sort of weather that mitigates its seve- 
rity, or seems to stay its progress. But although thus occurring 
in some measure irrespective of circumstances, yet a strict inquiry 
will, in many instances, disclose facts which before had eluded 
observation, and to the influence of which the disease may often be 
traced. The general principles of management may be sound, and 
the practice efficient, but still the predisposition to the disease may 
be referrible to the continued operation of some slight and appa- 
rently unimportant cause. 
Gutta caveat lapidem, non vi, sed saepe cadendo. 
“ The predisposing causes of pleuro-pneumonia admit of many 
divisions and subdivisions ; they may, however, be considered 
under two general heads , — hereditary and acquired. 
“ With reference to the former, we know that, as the good points 
and properties of an animal are transmitted from one generation 
to another, so also are the faults, and the tendencies to particular 
diseases. As in the same families there is a similarity of external 
form, so is there also an internal likeness, which accounts for the 
common nature of their constitution, modified, however, by differ- 
ence of age, sex, &c. 
“ Among the acquired predisposing causes of pleuro-pneumonia 
may be enumerated, general debility, local weakness resulting from 
previous disease, irritants and stimulants, exposure to cold, damp 
or sudden changes of temperature, the want of cleanliness, the 
breathing of an atmosphere vitiated by the decomposition of animal 
or vegetable matters, or laden with any other impurity. In short, 
under this head may be included every thing which tends to lower 
the health and vigour of the system, and consequently to increase 
the susceptibility to disease.” 
[To be continued]. 
