DISEASES OF THE BONES 387 



For an example of rarefactive ostitis as met with in cases 

 of disease of the feet, we refer the reader to laminitis (see 

 Fig. 118). The osteoplastic or condensing process that 

 appears to exist simultaneously with it explains, no doubt, 

 how it is that bones so affected do not more commonly 

 fracture. 



A further example of this process is illustrated in 

 Fig. 133. The pressure of a tumour (in this case a kera- 

 phyllocele) has led to rarefactive changes in the bone, 

 forming a neat indentation in the normal contour of the 

 bone which serves to accommodate the tumour. 



(b) Osteoplastic Ostitis, Osteosclerosis, or Condensation 

 of Bone. — This, too, is essentially a chronic process. It may 

 occur as a result of, or, as we have just shown, exist simul- 

 taneously with the condition of, diffuse rarefactive ostitis. 

 In this case there is a formation of new bone in the con- 

 nective tissue surrounding the vessels in the Haversian 

 canals. As a consequence the bone affected is greatly 

 increased in density, and many of the Haversian canals 

 by this means obliterated. The end result is an increase 

 in size of the bones in such positions as the horny box 

 admits of it, and a peculiar ivory-like change in their 

 consistence. 



For an example of this, we again refer the reader to the 

 changes occurring in chronic laminitis. 



(c) Caries and Necrosis. — Caries is a word which ap- 

 pears to be used with a considerable amount of looseness. 

 In addition to the meaning implied by necrosis (namely, 

 'death' of the part), caries is generally used to indicate 

 that there is also a condition of rottenness, decay, and 

 stench. It is particularly applied, in fact, when the death 

 of the bone is slowly progressive, and is due to the inroads 

 made upon it by putrefactive or septic matter. 



Necrosis of bone may be the result of an injury, such as 

 severe blows, or pricks and stabs. In such cases it would 

 appear that it is loss of a portion of periosteum that is the 

 starting-point. With death of a portion of this membrane 

 the vascular supply to a portion of the bone is cut off, and 



