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.

_Diagnosis of Sarcoma._--A sarcoma is to be differentiated from an
inflammatory swelling such as results from tubercle, actinomycosis, or