umbers scattered throughout the marrow. The parts
of the skeleton most often affected are the articular ends of the long
bones, the bodies of the vertebrae, and the pelvis.

As the cysts increase in number and in size, the framework of the bone
is gradually absorbed, and there result excavations or cavities. The
marrow and spongy bone first disappear, the compact tissue then becomes
thin, and pathological fracture may result. The bone becomes expanded,
and the cysts may escape through perforations into the surrounding
cellular tissue, and when thus freed from confinement may attain
considerable dimensions. Suppuration from superadded pyogenic infection
may be attended with extensive necrosis, and lead to disorganisation of
the adjacent joint.

_Clinical Features._--The patient complains of deep-seated pains. In
superficial bones, such as the tibia, there is enlargement, and it may
be possible to recognise egg-shell crackling, or unequal consistence of
the bone, which is hard in some parts, and doughy and elastic in others.
The disease may pursue an indolent course during months or years until
some complication occurs, such as suppuration or fracture. With the
occurrence of suppuration the disease becomes more active, and abscesses
may form in the soft parts and in the adjacent joint. In the vertebral
column, hydatids give rise to angular deformity and paraplegia. In the
pelvis, there is usually great enlargement of the bones, and when
suppuration occurs it is apt to infect the hip-joint and to terminate
fatally.

Examination with the X-rays shows the characteristic excavations of the
bone caused by the cysts. The disease is liable to be mistaken for
central tumour, gumma, tuberculosis, or abscess of bone.

The _treatment_ consists in thorough eradication of the parasite by
operation. The bone is laid open and scraped or resected according to
the extent of the disease, and the raw surfaces swabbed with 1 per cent.
formalin. In advanced cases complicated with spontaneous fracture or
with suppuration, amputation affords the best chance of recovery.

The lesions in the bones resulting from _actinomycosis_ and from
_mycetoma_, have been described with these diseases.

CONSTITUTIONAL DISEASES ATTENDED WITH LESIONS IN THE BONES

These include rickets, scurvy-rickets, osteomalacia, ostitis deformans,
osteomyelitis fibrosa, fragilitas ossium, and diseases of the nervous
system.

RICKETS

Rickets or rachitis is a c