ma, from chronic forms of
staphylococcal osteomyelitis, from enlarged bursa or ganglion, from
sub-periosteal lipoma, and from sarcoma. Most difficulty is met with in
relation to periosteal sarcoma, which must be differentiated either by
the X-ray appearances or by an exploratory incision.

_X-ray appearances in periosteal tubercle_: the surface of the cortical
bone in the area of disease is roughened and irregular by erosion, and
in the vicinity there may be a deposit of new bone on the surface,
particularly if a sinus is present and mixed infection has occurred; in
_syphilis_ the shadow of the bone is denser as a result of sclerosis,
and there is usually more new bone on the surface--hyperostosis; in
_periosteal sarcoma_ there is greater erosion and consequently greater
irregularity in the contour of the cortical bone, and frequently there
is evidence of formation of bone in the form of characteristic spicules
projecting from the surface at a right angle.

The early recognition of periosteal lesions in the articular ends of
bones is of importance, as the disease, if left to itself, is liable to
spread to the adjacent joint.

The _treatment_ is that of tuberculous lesions in general; if
conservative measures fail, the choice lies between the injection of
iodoform, and removal of the infected tissues with the sharp spoon. In
the ribs it is more satisfactory to remove the diseased portion of bone
along with the wall of the associated abscess or sinus. If all the
tubercle has been removed and there is no pyogenic infection, the wound
is stitched up with the object of obtaining primary union; otherwise it
is treated by the open method.

#Tuberculous Osteomyelitis.#--Tuberculous lesions in the marrow occur as
isolated or as multiple foci of granulation tissue, which replace the
marrow and erode the trabeculae of bone in the vicinity (Fig. 124). The
individual focus varies in size from a pea to a walnut. The changes that
ensue resemble in character those in other tissues, and the extent of
the destruction varies according to the way in which the tubercle
bacillus and the marrow interact upon one another. The granulation
tissue may undergo caseation and liquefaction, or may become
encapsulated by fibrous tissue--"encysted tubercle."

[Illustration: FIG. 124.--Tuberculous Osteomyelitis of Os Magnum,
excised from a boy aet. 8. Note well-defined caseous focus, with several
minute foci in surrounding marrow.]

Sometimes the