n a variety of ways. First, of course, will come errors in
diagnosis. No one of us is infallible, and the lameness we have judged as
resulting from side-bone may arise from another cause. There are, too,
complications to be reckoned with, the existence or absence of which cannot
always be definitely ascertained. Such are: Ringbone, especially that form
of ringbone known as 'low'; bony deposits on the pedal bone, either on its
laminal or plantar surface, or even changes in the navicular bursa.

CHAPTER XI

DISEASES OF THE BONES

A. PERIOSTITIS AND OSTITIS.

We head this section, Periostitis _and_ Ostitis, for the reason that in
actual practice it is rare for one of these affections to occur without the
other. The periosteum and the bone are so intimately connected that it is
difficult to conceive of disease of the one failing to communicate itself
in some degree to the other. Pathologically, however, and for purposes of
description, it is more convenient to describe separately the abnormal
changes occurring in these two tissues.

With the main phenomena of inflammation occurring elsewhere we presume
our readers are aware. Briefly we may put it, that under the action of an
irritant, either actual injury, chemical action, or septic infection,
the healthy tissues around react in order to effect repair of the parts
destroyed. Also that this reaction involves the distribution of a greater
blood-supply to the part, with an abundant migration of leucocytes, and
the outpouring of an inflammatory exudate, together with symptoms of heat,
pain, redness, and swelling of the affected area. And that in chronic
inflammations, owing to persistence of the cause, the process of repair
thus instituted does not stop at mere restoration of lost tissue, but
continues to the extent of forming an abnormal quantity of such tissue as
normally exists in the parts implicated.

The process of inflammation in bone is essentially the same. It takes place
along the course of the bloodvessels, and is only modified in its attendant
phenomena by the structure of the parts involved. Swelling, for instance,
cannot take place in the centre of compact bone tissue. Otherwise, other
changes occur exactly as in inflammations of other structures.

When the causal irritant has been excessively severe and the migration of
leucocytes abundant, actual formation of pus may occur, the bony tissue
being broken down and mingled with it, and an abscess cavity