In its growth, a sarcoma compresses and destroys neighbouring parts, surrounds vessels and nerves, and may lead to destruction of the skin, either by invading it, or more commonly by causing sloughing from pressure.  Inflammatory and suppurative changes may take place as a result of pyogenic infection following upon sloughing of the overlying skin or upon an exploratory incision.  Once the skin is broken the tumour fungates through the opening.  Sarcomas vary in malignancy, especially as regards rapidity of growth and capacity for dissemination.  Certain of them, such as the so-called “recurrent fibroid of Paget,” grow comparatively slowly, and are only malignant in the sense that they tend to recur locally after removal; others—­especially the more cellular ones—­grow with extreme rapidity, and are early disseminated throughout the body, resembling in these respects the most malignant forms of cancer.  They are usually solitary in the first instance, although primary multiple growths are occasionally met with in the skin and in the bones.

Many varieties of sarcoma are recognised, according to its structural peculiarities.  Thus, in virtue of the size and character of the cells, we have the small round-celled and the large round-celled sarcoma, the small and the large spindle-celled, the giant-celled and the mixed-celled sarcoma.  The lympho-sarcoma presents a structure similar to that of lymph-follicular tissue, and the alveolar sarcoma an arrangement of cells in alveoli resembling that seen in cancers.  When there is a considerable amount of intercellular fibrous tissue, the tumour is called a fibro-sarcoma.

[Illustration:  FIG. 56.—­Fungating Sarcoma of Arm.

(Dr. J. M’Watt’s case.)]

The term lymphangio-sarcoma is applied when the cells of the tumour are derived from the endothelium of lymph spaces and vessels.  The angio-sarcomas are those in which blood vessels form a prominent element in the structure of the tumour.  They are sometimes derived from innocent angiomas, and they may be so vascular as to pulsate and on auscultation yield a blowing murmur like an aneurysm.  The glio-sarcoma, myxo-sarcoma, chondro-sarcoma, and myo-sarcoma are mixed forms which usually develop in pre-existing innocent tumours.  The osteo-sarcoma is characterised by the formation in the tumour of bone, the medullary spaces being occupied by sarcomatous cells in place of marrow.  The osteoid sarcoma is characterised by the formation of a tissue resembling bone but deficient in lime salts, and the petrifying sarcoma by the formation of calcified areas in the stroma.  These varieties, although met with chiefly in the bones, may occur in soft tissues such as muscle, and in such organs as the mamma.  The pigmented varieties include the chloroma, which is of a light-green colour, and the melanotic sarcoma, which is brown or black.  The psammoma is a sarcoma containing a material resembling sand; it is chiefly met with in the membranes of the brain.  The chordoma is a rare form of tumour originating from the remains of the notochord in the region of the spheno-occipital synchondrosis or in the sacro-coccygeal region.