tter for research. We may, however, sum the
matter up by briefly discussing the causes, so far as clinical observation
teaches us. This we shall do under two headings--namely, _Predisposing_ and
_Exciting_.

_Predisposing Causes_.--Starting with the assumption that the disease is
due to local infection, we may relate as predisposing causes anything
having a prejudicial effect upon the horn, disintegrating it, and so laying
the tissues beneath open to attack. The most prominent in this connection
is certainly a continued dampness of the material on which the animal
has to stand. Particularly is this the case when the material is also
excessively foul and dirty, contaminated with the animal discharges, and
presumably swarming with the lower forms of animal and plant life. We
shall therefore find bad cases of canker in stables where the "sets" are
irregular, or where no paving at all is attempted, where the drainage
is defective, and where darkness and want of proper ventilation favours
organismal growth. The fact that with modern drainage and a general
hygienic improvement in stabling, canker has to a large extent died out,
supports this contention.

Again, as with thrush, anything removing the counter-pressure of the frog
with the ground and throwing that organ out of play, may be looked upon
as a predisposing cause. The atrophy of the frog thus occurring, the
deterioration in the quality of its horn and the fissures in its surface
lay it specially open to infection. That one of the principal factors in
the treatment of canker is a restoration of ground-pressure to the frog and
the sole is sufficient proof of this.

Further, it is well to note that, although playing no part in the actual
causation, certain constitutional conditions may in some measure predispose
the foot to attack. Clinical observation teaches us that animals of a
lymphatic nature, with thick skins and an abundance of hair, with flat feet
and thick, fleshy frogs, are far more liable to attack than are animals
with reverse points.

_Exciting Causes_. Those who give this subject careful consideration cannot
fail to arrive at the conclusion that canker is most certainly due to local
infection with a specific poison, and that poison a germicidal one from the
ground. The symptoms arising may be due to the action of a single germ, or
to two or more germs acting in conjunction. As to whether the parasitic
invasion is single or multiple we cannot feel certain