382 DISEASES OF THE HOESE'S FOOT 



cavity is extremely small — almost nil, in fact — which explains 

 in some measure how easy it is when suppuration exists to 

 get necrosis and exfoliation of, say, portions of the os pedis. 

 Necrosis and sloughing of the periosteum itself may also 

 happen, but as the extreme vascularity of the membrane is 

 a fairly strong safeguard against that it is of only rare 

 occurrence. 



In connection with the deep layer of the periosteum, and 

 forming part of it, are found numerous bone-forming cells 

 (osteoblasts). These, under ordinary conditions, are relatively 

 quiescent. Under the slightest irritation or stimulation, 

 however, their bone-forming functions are stirred into 

 abnormal activity, thus explaining how easy it is (especially 

 with bones so open to receive slight injuries as are those of 

 the foot) to get ossific deposits, the starting-point of which 

 we are quite unable to account for. 



With this brief introduction we will now describe such 

 pathological changes as occur in the separate structures, 

 and which we are likely to encounter in the various diseases 

 of the foot. While so doing, we shall draw attention to such 

 diseases as we have previously described in which the 

 pathological conditions we are considering may be met with. 



1. Periostitis. 



This we shall consider under (a) Simple Acute Periostitis, 

 (h) Suppurative Periostitis, (c) Osteoplastic Periostitis. 



[a) Simple Acute Periostitis. — This is the periostitis that 

 follows on the infliction of a slight injury to the membrane 

 — an injury without an actual wound and free from infective 

 material. It is one, therefore, which we always judge as 

 existing in those cases where we have distinct evidence or 

 history of injury, but in which the injury has not been 

 severe enough to lead to fracture or to the infliction of an 

 actual wound. 



Such cases may be those of lamenesses persisting after 

 violent blows upon the foot — cases where the animal has 

 been kicking against the stable fittings, or where the foot 



