eir state of
health is so weakened that they are unable to successfully combat with the
two conditions simultaneously. As a consequence, the necrotic piece of bone
persists, and acts as a permanent source of irritation.

It must be remembered, too, that if the dead portion of bone--even though
it be free from septic matter--is very large, that it may itself act as a
continual irritant, in which case it again persists, and cannot by natural
means be removed.

In our cases necrosis of bone may be met with in punctured foot, in severe
cases of tread, in cases of complicated crack, and in suppurating corn.
It is met with, too, in navicular disease, in the extension of irritating
discharges in cases of quittor, and in cases of chronic laminitis where the
solar margin of the os pedis has penetrated the sole. In this latter case
the protruding portion of bone is quickly denuded of its periosteum. Its
blood-supply is destroyed, and necrosis follows.

_Treatment_.--In simple cases of periostitis, those caused by a blow but
free from an actual wound, the most beneficial treatment is the continued
application of cold by means of a hose-pipe or by swabs. If by these means
we are successful in holding the inflammatory phenomena in check, any large
formation of new bone is prevented, and the case does well.

When the case is complicated by a wound, then antiseptic measures, such as
those described in the treatment of punctured foot, will at the same time
have to be practised.

It must be admitted, however, that in all but the most simple cases
ordinary treatment such as this is of very little use; for with only a
slight exostosis in almost any position in the foot, excessive lameness
presents itself and remains. In such cases nothing is left to us but the
operation of neurectomy.

When the periostitis and ostitis is the result of a wound, and is
complicated by caries or necrosis of the bone, the diseased portion of
bone must in every case be laid bare and removed. It so happens that the
majority of cases of this kind occur in positions where the diseased bone
is easily got at. The lower margin of the os pedis or portions of the wings
are commonly the seat of such changes. We meet with the former in cases
of pricked foot, and with the latter in severe cases of tread, or as a
complication in suppurating corn or in quittor. In such cases the animal
must be cast and the foot secured. The wound is then followed up, the horn
if neces