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. _Diagnosis of Sarcoma._--A sarcoma is to be differentiated from an inflammatory swelling such as results from tubercle, actinomycosis, or syphilis, from an innocent tumour, and from a cancer. The points on which the diagnosis is founded are discussed with the different tissues and organs. _Treatment._--The removal of the tumour by operation is the most reliable method of treatment; in order to be successful it must be undertaken before dissemination has taken place, and a considerable area of healthy tissue beyond the apparent margin of the growth must be removed, and in tumours near the surface of the body, the overlying skin also.