g upon a bedding which, although dry, is
of unsuitable material.

In this latter connection may be mentioned the harm resulting from the use
of certain varieties of moss litter. This we find pointed out by J. Roalfe
Cox, F.R.C.V.S.[A] Tenderness in the foot was first noticed, and, on
examination, the horn of the sole and of the frog was found to be
peculiarly softened. It afforded a yielding sensation to the finger, not
unlike that which is imparted by indiarubber, and on cutting the altered
horn it was almost as easily sliced as cheese-rind. The outer surface
being in this way slightly pared off, the deeper substance of the horn was
discoloured by a pinkish stain. The horn of the frog was in many instances
found detaching from the vascular surface, which was very disposed to take
on a diseased action, somewhat allied to canker, and became extremely
difficult to treat.

[Footnote A: _Veterinary Journal_, vol. xvi., p. 243.]

Conditions such as these, although not constituting the disease itself,
certainly lay the frog open to infection, especially if afterwards the
animal is called upon to work in the mud of the streets of a large town, or
to stand in a badly drained and damp stable.

A further cause of thrush is to be found in the condition of the frog,
brought about by contraction of the heels (see p. 118). We have already
seen that one of the most prominent factors in the causation of contraction
is the removal of the frog from the ground by shoeing, with its consequent
diminution in size and deterioration in quality of horn. This leads to
fissures in the horny covering, and favours infection of the sensitive
structures beneath. Thrush is, in fact, nearly always present in the later
stages of contracted foot.

By some thrush is believed to be but the commencement of canker. With this,
however, we do not hold. We believe both to be due to specific causes as
yet undiscovered, but that the cause of thrush is not the one operating in
canker. In arriving at this conclusion we are guided by clinical evidence.
The two conditions are quite dissimilar, even in appearance, and, while
one is readily amenable to treatment, the other is just as obstinately
resistant.

_Symptoms_.--The symptoms of thrush are always very evident. Probably the
first thing that draws one's attention to it is the stench of the puriform
discharge. The foot is then picked up and the characteristic putrescent
matter found to be accumulated in the m