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. 1383. 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 appears 
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 any 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 
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