e horn. This is doubtless due to the poultice removing the thin,
varnish-like, and protective pellicle known as the periople, and thereby
allowing the process of evaporation to act on the water normally contained
in the hoof.

_Exciting Causes of Contraction_.--Among these, first place must
undoubtedly be given to shoeing. This does not necessarily imply shoeing
more than ordinarily faulty, nor a faulty preparation of the foot, but
shoeing as it is generally practised. No ordinary shoe, except a few
devised for the purpose, such as the Charlier or the tip, allows the frog
to come in contact with the ground. This we take to be the main factor in
the causation of contracted heels, especially with a predisposition already
present in the foot itself. In the words of Lungwitz: 'Regarded from this
point of view, there is no greater evil than shoeing. It abolishes the
necessary counter-pressure, and thus interferes with expansion. Bars, sole,
and frog cannot perform the functions that naturally belong to them as they
would do without the shoe.'

In addition to the evil of the shoe itself, errors of practice in the forge
contribute to the causation of contraction. Taking first the preparation of
the foot, we find that often the heels are lowered far too much, and the
toe allowed to remain too long. This can have but one effect--that of
throwing a greater proportion of the animal's weight upon the heels than
properly they should bear, with, what we now know to be the consequence of
that, a corresponding pushing inwards and downwards of the horn; in other
words, contraction.

Excessive paring of the bars, to which we have already partly alluded, is
also an active agent in bringing about an inward growth of the horn of the
heels and quarters. The bar, or inflexion of the wall at the heel, by means
of its close contact with the frog, communicates the outward movements
of that organ to the wall of the hoof. With the bar removed, the outward
movements of the frog under pressure are naturally rendered of no account,
and a proper and intermittent expansion of the wall denied it. The same
evil follows, though to a less extent, excessive paring of the sole.

The shape of the bearing surface of the shoe is often to be blamed. Where
this is concave--'seated'--and the 'seating' is carried back to the
heels, it is easy to see that, when weight is on the foot, there is an
ever-present tendency for the bearing edge of the wall to slide down