DISEASES OF THE BONES 385 



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 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 it were, compen- 

 sated for by rarefaction or bone-absorption changes occur- 

 ring simultaneously with it. 



25 



