(b) We are disposed to regard fat as an almost essential element of cancer, (or rather as a substance tending to be produced where ever cancer exists,) so constant is its appear ance, either in the oil-globule or the granule forms (adipose-cells, if present, come from the implicated natural tissue). When fat abounds in these growths, it appears to have the effect of altering the form of the cancer-cell, and certainly modifies the naked-eye characters of the tumour.
(c) The contingent materials met with in carcinoma are saline particles, crystalline (Op. cit. fig. 11) or amorphous and calca reous,—the latter in very rare instances accu mulating sufficiently to become perceptible to the naked ey e (calcification ;) cry stals of cholesterin and patches of cholesteatoma; per haps in very rare instances tuberculous depo sitt ; melanic matter ; blood fluid, clotted, in the state of fibrinous hmmatoma, or of " apoplectic cyst ;" exudation-tnatter with its spherical and fusiform cell ; pus ; and (on ulcerated surfaces) certain epizoa and epi phyta. The pseudo-tissues which may be actually formed within the area of cancer (any natural texture may be invested by cancer) are epithelium, the cellular, serous, fibrous, and elastic tissues and blood vessel. Spicu lated osteophytes, preceded (sometimes at least) by sprouting cartilage, not unfrequently plunge into the substance of cancerous growths from some connected part of the skeleton : an isolated generation of true bony structure, in a nidus of blood-blastema, within a cancerous tumour, seems a possible occur rence (it is at the least, a singularly rare one); but the possibility of such generation in actual cancer-substance seems only admissible on the principle that the freaks of nature are bound less in their variety.
Built up of materials, such as these, are all cancers. Encephaloid, soft, brain-like, rapid in its evolution, attaining great bulk, highly vas cular, prone to bleed and fungate, is microsco pically distinguished by its deficiency in fibrous stroma and the abundance of its fluid blastema and its cells. Scirrhus, hard, tough, slow in growth, and reaching moderate dimensions only, poor in vessels, rich in fibre, differs mi croscopically from its co-species in its abun dance of fibrous stroma and the comparative fewness of its cells, which mainly grow on the exogenous plan. Colloid, crisp in its mass, soft in the jelly-like ineredient that fills its loculi (models of the spherical loculus), but slightly vascular and semi-transparent, stands apart microscopically from encepha loid in the well-marked fibrousness of its loculus-walls, from scirrhus in the abundance of its endogenously-growing cells, from both in the abundance of its viscid jelly-like element.
The chemistry of cancer is yet in its in fancy. Its organic basis is essentially protein, —its saline constituents those of the blood. That there is a difference in chemical nature between colloid and the other species, seems plain from the fact that the former retains, the latter lose, their transparency in alcohol : Mil ler conjectures that colloid contains a com pound analogous to ptyalin. Microchemically
the cells of cancer are insoluble in cold and boiling water, and are not seriously affected (in respect of solution) by acetic acid : the cell-wall has been said to disappear under the influence of the diluted acid ; but it is simply rendered pale, and may be restored by the ioduretted solution of iodide of potassium, which at the same time greatly deepens the colour of the nucleus.
We have already said (p. 124) that a con stant and unfailing microscopical characteristic of cancer has hitherto been vainly sought for ; the following propositions will serve as a com mentary on, and, in some sort, a justification of, the statement. (1.) Parent cells, con taining within them sub-cells having darker nuclei, and these, in turn, bright nucleoli, are strongly characteristic of cancer : but such cells are rare in, and may be altogether absent from, scirrhus ; enceplialoid in some phases of its growth may also be without them. (2.) The shapelessly-caudate cell (see fig. 98) seems significant of cancer ; but it may be absent from encephaloid, and it is ex cessively rare in scirrhus or colloid, (3.) A tumour may present to the naked eye the cha racters of encephaloid, be the seat of interstitial hzemorrhage, affect the communicating lymph atic glands, run in all respects the course of cancer, and nevertheless contain no cells but such as are undistinguishable, in the present state of knowledge, from common exudation cells. (4.) Nay more, while a primary " malignant" tumour contains these cells alone, the lymphatic glands secondarily- af fected may contain compound nucleated cells, spherical and shapelessly-caudate.. (5.) The granular and imperfectly nucleated cell of scirrhus is valueless as an evidence of cancer.
(6.) The true fusiform cell (fig. 93) is an adventitious formation when it occurs in cancer, and has no dia,mostic sionification.
(7.) The association of fiCre and celr-structure, which will distinguish scirrhus from fibrous tumour, may be totally wanting in encepha loid, and exists in sarcoma and enchondroma.
(8.) If fat be associated in large quantity with fibre and cell-structure, the certainty that cancer is present becomes great, but not ab solute.
The property of infiltration, which serves well, as we have shown (p. 125), to distinguish cancer from other growths nosologically, fails practically in the distinction of tumours gene rally, because a true cancer is not necessarily infiltrated, and because tubercle and exuda tion-matter may be infiltrated. In ultimate analysis the single character least likely to deceive is this : if a tumour be cancerous, it will yield on pressure an opaque, whitish (niilky or creamy-looking) albuminous fluid t ; if it be not cancerous, it will not yield a fluid of these qualities.