l fracture is more common in central tumours, and sometimes
is the first sign that calls attention to the condition. Consolidation
rarely takes place, although there is often an attempt at union by the
formation of cartilaginous callus.

[Illustration: FIG. 149.--Central Sarcoma of Lower End of Femur,
invading the knee-joint.

(Museum of Royal College of Surgeons, Edinburgh.)]

[Illustration: FIG. 150.--Osseous Shell of Osteo-Sarcoma of Upper Third
of Femur, after maceration.]

The soft parts over the tumour for a long time preserve their normal
appearance; or they become oedematous, and the subcutaneous venous
network is evident through the skin. Elevation of the temperature over
the tumour, which may amount to two degrees or more, is a point of
diagnostic significance, as it suggests an inflammatory lesion.

The adjacent joint usually remains intact, although its movements may be
impaired by the bulk of the tumour or by effusion into the cavity.

Enlargement of the neighbouring lymph glands does not necessarily imply
that they have become infected with sarcoma for the enlargement may
disappear after removal of the primary growth; actual infection of the
glands, however, does sometimes occur, and in them the histological
structure of the parent tumour is reproduced.

To obtain a reasonable prospect of cure, the _diagnosis_ must be made at
an early stage. Great reliance is to be placed on information gained by
examination with the X-rays.

[Illustration: FIG. 151.--Radiogram of Osteo-Sarcoma of Upper Third
of Femur.]

_X-ray Appearances._--In periosteal tumours that do not ossify, there is
merely erosion of bone, and the shadow is not unlike that given by
caries; in ossifying tumours, the arrangement of the new bone on the
surface is characteristic, and when it takes the form of spicules at
right angles to the shaft, it is pathognomic.

In soft central tumours, there is disappearance of bone shadow in the
area of the tumour, while above and below or around this, the shadow is
that of normal bone right up to the clear area. In many respects the
X-ray appearances resemble those of myeloma. In tumours in which there
is a considerable amount of imperfectly formed new bone, this gives a
shadow which barely replaces that of the original bone, in parts it may
even add to it--the resulting picture differing widely in different
cases; but it is usually possible to differentiate it from that caused
by bacterial infect