MALIGNANT TUMORS. So rem a.—Sarcomat are tumors of the connective-tissue group. They differ from connective-tissue tumors in that the connective tissue of which the sarcomata are com posed is of the embryonal form. This has a very distinct hearing upon their malignancy, for, as has been already mentioned, embryonal tissues possess much greater powers of growth than do adult tissues. Sarcomata are usually classified according to the character and ar rangement of their cellular elements. Thus we have small round-celled, large round-celled. small spindle-celled, large spindle-celled, giant celled or myeloid, stellate-celled sarcoma, etc. The ends of long bones like the tibia and humerus are frequently affected. The mammary glands are sometimes the sites of sarcoma, as also the sheaths of peripheral nerves. Sarcoma is as a rule an affection of early life. From ten to forty it is most common, and 1111C0111111011 after the latter age. The two sexes are about equally susceptible.
Carrinonia.—Carcinomata are malignant tu mors of epithelial tissue. The epithelium is as varied in character as is normal epithelium. The epithelial elements are supported by a more or less abundant connective-tissue framework, or stroma, which forms bundles of fibres irregular in arrangement, and in the meshes of whieli are cavities or alveoli in which the epithelial cells lie loosely without any definite arrangement. In general the epithelial cells conform to the dif ferent normal types; but. we find, as is the case with all cancerous growths, an irregularity as to shape, size, and arrangement which is 11111C11 more marked than in normal epithelium.
And even in a carcinoma where a particular type of cell predominates. other forms of cell are frequently intermingled with the predom inating form.
Carcinoma occurs as a primary tumor in tis sues of epiblastie origin. It originates in any of the various forms of epithelium. It is not be lieved to occur as a primary tumor in such tis sues as hone, muscle, etc., which originate in other embryonic layers. Carcinoma may, however, involve any of the body tissues. When it involves tissues other than epithelial, it is probable that the growth is secondary, the pri tumor in epithelium being so small as to have passed unrecognized.
The very hard and firm form of carcinoma so common in the female breast is known as 'scirrhous cancer' or fibro-carcinoma. its hardness is due to the large amount of dense fibrous tissue, the cellular elements being comparatively few. Very soft car cinomata, made up almost entirely of cells with a minimum amount of connective tissue, are called 'Medullary cancer' or carcinoma molle. Melano-carcinomata are tumors in which more or less brown or blaek pigment is deposited in the cells or in the connective-tissue stroma. Carcinomata whose cells have undergone mucoid degeneration or whose stroma is of the type found in mucous connective tissue are known as `carcinoma myxomatodes.' Gelatinous ma is a form of carcinoma in which the cells be come filled with a translucent gelatinous mate rial. In some tumors these droplets of gelati nous substance, which have taken the place of the epithelial cells, coalesce to form considerable areas of gelatinous material. These areas fre quently give an alveolar appearance, for which reason this form of carcinoma is frequently re ferred to as 'alveolar carcinoma.' Epithelionm is a form of carcinoma which originates in squamous epithelium. The struc ture of the tumor tissue corresponds roughly to that of squamous epithelium as seen in the skin and mucous membranes. Thus there are flat tenet] squamous surface cells, irregular cells such as are found in the deeper layers of the skin, 'prickle' cells, enhoidal cells, etc. Not in frequently squamous cells are packed in to gether in crescentic forms known as epithelial `pearls.' Epithelioma 'epithelial cancer' is most common around the orifices of the body where skin and mucous membranes unite, as for example around the openings of the month, nose, eyes, vagina. etc. The malignancy of an epithe lionia depends much upon the growth powers of its cells and the extent to which these cells tend to infiltrate surrounding tissues. In general it may be said that epitheliomata are the most slow growing and least malignant of all forms of cancer. They may, however. recur unless completely removed and may form metastases.