bed, and when one considers the
thinness of the keratogenous membrane, one is bound to admit that changes
so grave occurring in it cannot fail to spread and infect the periosteum.

_(c) Osteoplastic Periostitis_.--This is more particularly a chronic
process, and is, as the suffix '_plastic_' indicates, associated with
bone-forming changes in the membrane. It may occur as a consequence of
slight but continued irritation, often without ascertainable origin (see
Case 2, p. 392), or it may be the sequel of acute disease.

In this form of periostitis the membrane is again swollen and more vascular
than in health, and is also easily separable from the bone. The exposed
bone is generally rough, in some cases even spicular, and the inner layer
of the removed membrane is rough and gritty to the touch--characters
imparted to it by numerous minute fragments of bone that have been torn
away with it from the more compact osseous tissue beneath.

The results of an osteoplastic periostitis are frequently met with in the
bones of the foot, and are described by veterinary writers under
such headings as 'Pedal Exostoses,' 'Ossifying Ostitis,' and 'Pedal
Ossification' (see Figs. 152, 153, 154, and 155). In many of these cases
the disease is purely chronic, and the original cause nearly always
wanting. When the foot has been subjected to laminitis of some weeks'
duration, the same condition is also met with, being at the same time
associated with rarefactive osteoplastic ostitis, conditions which we
shall shortly describe. Cases we have examined have undoubtedly shown this
condition of osteoplastic periostitis, the rarefactive and osteoplastic
changes in the bone itself, met with in older cases, occurring no doubt
as a result of non-expansion of the horny box. So far as we are able to
ascertain, there is every reason to believe that in chronic laminitis the
accompanying periostitis leads to the formation of bone, and would, if it
were possible, lead to increase in the size of the os pedis. If proof were
wanted of this, it is only necessary to point out the increased growth at
points where resistance is nil--namely, along the upper margin of the bone
(see Fig. 118). However, increase in size elsewhere is prevented by the
resistance of the hoof, so that, as the bone-forming process progresses, as
it inevitably _must_ under the inflammatory changes going on, it is, as it
were, compensated for by rarefaction or bone-absorption changes occurrin