DISEASES OF THE BONES 385 
irritation, often without ascertainable origin (see Case 2 
p. 892), 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 separ- 
able 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 rare- 
factive 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 accom- 
panying 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 pre- 
vented 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 ib were, compen- 
sated for by rarefaction or bone-absorption changes occur- 
ring simultaneously with it. 
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