Cancer (Latin, cancer, a crab—Carcinoma).— The name of this disease is derived from the appearance of the part attacked by the disease, as it struck the ancients, the veins surrounding the diseased part resembling a crab's claw.
Cancer is considered in this section more as a matter of convenience. It is still a question much discussed whether cancer ought to be counted a local or a constitutional disease, and many reasons can be adduced for answering the question either way. It is certain, how ever, that after cancer has appeared in any part, however small and limited its position may be, and however insignificant it may appear, it will in time spread along various channels and affect the whole system.
Nature.—Its character is that of a tumour, swelling, growth, or deposit which tends to spread, not simply by becoming larger and squeezing aside the healthy substance of the part in which it is placed to make room for itself, hut by growing into the healthy parts, invading them, and incorporating them into itself. It can never, therefore, be removed from its position as a whole without other parts being disturbed, but if removed the whole 1118.98 of tissue in which it is placed must he cut out with it. Moreover, even if removed, it tends sooner or later to return, perhaps just because it so invades the tissues that it is impossible to make sure that all of it has been removed. This feature of it is one of the chief reasons why it is called " malig nant." For it is evident that a tumour whose tendency is always to return to the attack is likely some day to overcome its victim. A "simple" tumour, however, is one which, once removed, is done with. Not only does cancer tend to spread by direct invasion of the sub stance of the part where it is placed, but it also tends to spread to distant parts by convey ance along vessels. Blood-vessels are doubtless channels along which particles of cancerous material may be carried to parts at some distance from the original growth, and which, taking root in the new situation, proceed to grow and form a secondary tumour. Other channels which afford au even readier means of transit are the lymphatic vessels, which, as has been noted on p. 278, are found in every tissue of the body as drains for the removal of excessive nourishment supplied to the part, and also for the removal of waste products. Into these channels, therefore, juice and particles from the tumour will find their way. The lymphatic vessels pass to lymphatic glands in order that the material they carry may be worked up into a fit state for return to the blood. Thus it is that some time after a
cancerous tumour has appeared in some part of the body the glands in the neighbourhood are almost certain to be found enlarged and otherwise affected. It is this that renders it so difficult to remove a cancerous growth with any certainty of permanent cure. For the cancerous material may have been carried con siderable distances from the original tumour by such channels, without any signs of the transference being. evident for a long time. It is this also that renders it imperative that a cancerous growth should be remorselessly cut out as soon as it is discovered, and the smaller and more insignificant the growth appears the more eager should the patient be for its removal. But it is just at this stage of its growth that patients are indis posed to permit an operation. It is so small, or it gives so little, perhaps no trouble, is the need of operating at present? Wait till it is bigger, painful, troublesome, then the patient will consent. It is necessary earnestly to insist on the undoubted fact, the reasons for which have just been given, that it is while the growth is small and trifling that its removal is most hopeful, and that waiting till it is bigger means practically waiting till it is hopeless.
As to the nature of the growth itself, cancer is essentially formed of a degenerate kind of cell, and is originally connected with structures mainly of the epithelial type (see p. 55). Thus the surface layer of the skin consists of epi thelial cells (p. 412), the mucous membrane of the mouth has a similar superficial layer (p. 195); the stomach and whole length of the intestinal canal (p. 198) has an outer most layer of cells; the membrane covering the windpipe and tubes of the lungs, as well as the air spaces of the lung themselves, are covered with epithelial cells (p. 343); the kid ney and bladder have similar inner coatings (pp. 394, :398), while glands—the salivary glands (p. 196), the glands of the stomach and intestine (p. 199)--are also lined with epithelial cells. Now it is in these situations and others of a similar character that cancer is found, the cells coming under some degenerative influence, which causes them to multiply in enormous numbers and thus to invade the surrounding tissues and form deposits. The cells are held together by a small amount of connective tissue (p. 56), in whose spaces the cells lie. A cancer tumour is thus a growth formed of masses of cells in groups held together by connective tissue, the cells being originally derived from the natural cells of the part.