PRACTICE OF VETERINARY MEDICINE AND SURGERY. 819 
mark out and name the varying character of the agencies or 
influences recognised in the department of etiology. We 
speak of causes as predisposing when there are such, whatever 
may be the nature of the influence which seems to act un¬ 
favorably in influencing the functions or structures of the 
body, rendering it more liable than it would otherwise be 
to exhibit actual disease; as exciting when by their imme¬ 
diate action on the animal body, more particularly when pre¬ 
disposed disease is the result; as external or internal when 
the inducing agent acts from within or without the body. 
We also speak of aptitude or predisposition and of idio¬ 
syncrasy when the animal within itself possesses some 
peculiar tendency to or power of resistance of adverse influ¬ 
ences ; and of influences epizootic and enzootic when dis¬ 
eases originate over extensive districts of a country, the 
causes of which are inappreciable, or where they are con¬ 
fined to some particular locality, the causes being obvious, 
and confined to the place of their existence. 
In following out the study of the practice of medi¬ 
cine and of special equine pathology, which is in reality 
the recognition of veterinary medicine and surgery as 
an art, inasmuch as it is directed to observe and to 
ascertain, as far as possible, the causes, the nature, the 
means of cure or of alleviation, and the most successful 
modes of the prevention of disease in the horse, it will be 
for our advantage, at this particular stage, to recognise and 
examine those large and general sources of information, 
those channels through which symptoms of derangement are 
exhibited, and from which signs of disease are collected, and 
by which we are led to understand the causes or factors 
which may have induced this derangement or disease, and 
the localities and textures specially the seat of morbid 
changes—all which are needful to qualify us for giving a 
place to any diseased process or condition, in whatever 
system of nosology or naming of disease we may choose to 
adopt. 
Sources of our Knowledge in Disease. 
The chief sources or channels through which, in disease, 
are exhibited those phenomena which, when collected, com¬ 
pared, and associated with mind, constitute what we speak 
of and regard as positive knowledge in relation to both the 
nature, character, developmen and probable results of 
disease, are— 
1st. Those associated with or drawn from a consideration 
of the condition of the pulse. 2nd. The state of the visible 
