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 infections of the bone and from lesions of the adjacent joint.

[Illustration:  FIG. 152.—­Radiogram of Chondro-Sarcoma of Upper End of Humerus in a woman aet. 29.]

Skiagraphy is not only of assistance in differentiating new growths from other diseases of bone, but may also yield information as to the situation and nature of the tumour, which may have important bearings on its treatment by operation.

When fracture of a long bone takes place in an adolescent or young adult from comparatively slight violence, disease of the bone should be suspected and an X-ray examination made.

In difficult cases the final appeal is to exploratory incision and microscopical examination of a portion of the tumour; this should be done when the major operation has been arranged for, the surgeon waiting until the examination is completed.

The prognosis varies widely.  In general, it may be said that periosteal tumours are less favourable than central ones, because they are more liable to give rise to metastases.  Permanent cures are unfortunately the exception.

Treatment.—­When one of the bones of a limb is involved, the usual practice has been to perform amputation well above the growth, and this may still be recommended as a routine procedure.  There are reasons, however, which may be urged against its continuance.  High amputation is unnecessary in the more benign sarcomas, and in the more malignant forms is usually unavailing to prevent a fatal issue either from local recurrence or from metastases in the lungs or elsewhere.  Following the lead of Mikulicz, a considerable number of permanent cures have been obtained by resecting the portion of bone which is the seat of the tumour, and substituting for it a corresponding portion from the tibia or fibula of the other limb.  In a cellular sarcoma of the humerus of a boy we resected the shaft and inserted his fibula ten years ago, and he shows no sign of recurrence.  When resection is impracticable, a subcapsular enucleation is performed, followed by the insertion of radium.

#Pulsating Haematoma# or #Aneurysm of Bone#.—­A limited number of these are innocent cavernous tumours dating from a congenital angioma.  The majority would appear to be the result of changes in a sarcoma, endothelioma, or myeloma.  The tumour tissue largely disappears, while the vessels and vascular spaces undergo a remarkable development.  The tumour may come to be represented by one large blood-containing space communicating with the arteries of the limb; the walls of the space consist of the remains of the original tumour, plus a shell of bone of varying thickness.  The most common seats of the condition are the lower end of the femur, the upper end of the tibia, and the bones of the pelvis.