d the existence of
ailments, local and general, are all to be taken into account.

Among horses, those employed in heavy draft work or that are driven over
bad roads are more exposed than light-draft or saddle horses, and
animals of different ages are not equally liable. Dogs and young horses,
with those which have become sufficiently aged for their bones to have
acquired an enhanced degree of frangibility, are more liable than those
which have not exceeded the time of their prime. The season of the year
is undoubtedly, though in an incidental way, an important factor in the
problem of the etiology of these accidents, for though they may be
observed at all times, it is during the months when the slippery
condition of the icy roads renders it difficult for both men and beasts
to keep their feet that they occur most frequently. The long bones,
those especially which belong to the extremities, are most frequently
the seat of fractures, from the circumstance of their superficial
position, their exposure to contact and collision, and the violent
muscular efforts involved both in their constant, rapid movement and
their labor in the shafts or at the pole of heavy and heavily laden
carriages.

The relation between sundry idiosyncrasies and diathesis and a liability
to fractures is too constant and well-established a pathological fact to
need more than a passing reference. The history of rachitis, of
melanosis, and of osteoporosis, as related to an abnormal frangibility
of the bones, is a part of our common medical knowledge. There are few
persons who have not known of cases among their friends of frequent and
almost spontaneous fractures, or at least of such as seem to be produced
by the slightest and most inadequate violence, and there is no tangible
reason for doubting an analogous condition in dividuals of the equine
race. Among local predisposing causes mention must not be omitted of
such bony diseases as caries, tuberculosis, and others of the same
class.

Exciting, occasional, or "efficient" causes of fracture are in most
instances external traumatisms, as violent contacts, collisions, falls,
etc., or sudden muscular contractions. These external accidents are
various in their character, and are usually associated with quick
muscular exertion. A violent, ineffectual effort to move too heavy a
load; a semispasmodic bracing of the frame to avoid a fall or resist a
pressure; a quick jump to escape a blow; stopping too sud