e, 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 simultaneously with the condition of, diffuse
rarefactive ostitis. In this case there is a formation of new bone in the
connective 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 necrosis ensues. It may also result from the extension of inflammatory
affections of the structures adjoining it, as, for instance, the spread of
the infective material in severe tread, or the encroaches made by pus in
cases of quittor, suppurating corn, or complicated sand-crack.

When the necrosed portion of bone is small, and is free from infective
properties, it is quite possible that it may, as is the case with small
spots of necrosis in softer tissues, be removed by a process of absorption.
It must be remembered, however, that where the necrosis has occurred as a
result of septic invasion this cannot be looked for, for in every case such
reparative changes are worked solely by healthy tissue. If the tissues
around the necrosis are engaged in dealing with organismal invasion and
the poisonous products thus poured into their working area, th