Page:EB1911 - Volume 27.djvu/390

connective tissue is almost non-existent and the cells are essentially of an embryonic type. These differences between the innocent and the malignant cell bear out the well-established physiological rule that the less the functional development of a cell or tissue the greater its power of growth. The primitive impulse is growth, which gives place at a later stage to the development of function.

Site of ulcer

FIG. 4.-Malignant tumour (epithelioma, squamous-celled carcinoma) of the skin. The cells of the epidermis have proliferated both outwardly and inwardly and have invaded and replaced the underlying tissues. An ulcer has been formed on the surface by the necrosis of the superficial cells. (Semidiagrammatic.) In theory it is always possible to distinguish with certainty between an innocent tumour and a cancer by means of the microscope. In practice this is, unfortunately, not the case. There are some tumours whose histological appearances seem to be on the borderline between the two conditions, and often these are the very cases in which the clinical features give no direct clue to their nature. In such circumstances it is only 'by taking into consideration every detail, both clinical and pathological, that an opinion can beformulateg, and even then it remains to some extent a matter of guessw'OI

The Causation of Tumours.-An enormous number of suggestions as to the causation of tumours have been put forward from time to time. Many of these were at the outset quite untenable, and reference can only be made here to the more important. First in point of time came Vircho'w's hypothesis that tumours arise as the direct result of irritation or injury. Many examples of such a sequence of events are familiar to everybody. A cancer of the lip or tongue will often follow the irritation of a clay pipe or a jagged tooth; a tumour of the breast is often attributmil to a blow. But, on the other hand, there must be innumerable instances in which such a cause of irritation has not been followed by a tumour; and it is necessary to discount the natural anxiety of mankind to seek a cause for every unexplained occurrence, so that a slight injury which under ordinary circumstances would be forgottenlis branded as the undoubted cause of any tumour that may subsequently make its appearance. As a complete explanation Virchow's hypothesis is insufficient, but it is quite probable that irritation may have an accessory or predisposing influence in tumour formation, and that it may be enough finally to upset the balance of a group of cells, which for some other reason were already hovering on the brink of abnormal growth.,

There is one peculiar .form or irritation that demands special attention, that is exposure to the X rays. It is beyond doubt that exposure to these rays will cause cancerous ulceration of the skin; though what is the constituent of the rays that produces this effect is not known. Fortunately the danger can be obviated by the use of rubber gloves.

C0hnheim's Hypothesis of Embryonic Remnants.—According to Coh nheim more cells are produced in embryonic life than are required for the development of the body, and a remnant is left unappropriated. Dwing to their embryonic nature, these cells possess an exaggerated power of proliferation, and if at a later period- of life this should be roused into activity by some mechanical or other form of stimulus, their rate of growth will outstrip that of the adult cells and a tumour will develop. As with Virchow's so with Cohnheim's hypothesis. It is at best only a partial explanation which may be applicable to a small proportion of tumours; and it could never account for X-ray cancer, or the inoculability of mouse cancer. .

The Parasitic hypothesis is still a matter of keen debate. In some degree cancer with its localized primary growth and widespread secondary deposits resembles certain infective diseases of microbial origin, such as pyaemia, where from a small prima site of infection the bacteria become disseminated throughout thergody. From this analogy it was argued that tumour formation was due to the activity of some parasite. But if the mode of dissemination of a cancer and of aimicro-organism be carefully examined this analogy is found to be false. When a micro-organism lodges in a gland or other art of the body, by its irritative action it stimulates the cells of that gfand to increased activity, and any swelling that occurs is produced by the proliferation of those cells. But when a group of cancer-cells is deposited in a gland the subsequent growth arises entirely from the multiplication of those cancer-cells, and the gland cells take no part whatever in its formation.,

A very large number of organisms both -animal and vegetable have been described as occurring in tumours; and some of these have been cultivated on artificial media outside the body; but to none of them can any direct causal relationship with cancer be attributed. One of the best authenticated, a small coccus, known as .Mierococcus neoforrnans can certainly be cultivated from many tumours malignant and innocent, and it has been suggested that it may be responsible for the slight inflammatory changes that occur in the neighbourhood of most new growths. The final and critical test of the connexion of an organism with some diseased condition is the production of a similar condition in animals by inoculation of that organism, and this experiment has signally failed with all the suggested cancer parasites. Another very cogent argument against the infective hypothesis is the fact that although tumours of identical structure are found throughout the vertebrate kingdom, it has never yet been found possible artificially to transmit these tumours from one species to another. If they were of an infective nature it is almost inconceivable that the gap between two allied species should be such an insuperable bar to transmission.

Quite recently Borrel of the Pasteur Institute has stated that certain animal parasites from the skin are often to be found buried in the cell masses of cancers of the skin and breast, and he thinks that these parasites may be the carriers of some as yet unknown cancer virus, just as the mosquito is the carrier of malaria. Ribbert has suggested that tumour formation may be due to “ alteration of tissue tension.” In his opinion the various cells of the body are normally held in a state of equilibrium by some condition of mutual interdependence . amongst themselves. Should this equilibrium be disturbed some of 'these cells may escape from the controlling influence usually exercised upon them by their neighfilours, and become endowed with greatly enhanced powers of rowt .

g Adami considers that every cell possesses two distinct roper ties, a property of function and a property of growth, and fic regards these as incompatible, that is to say, a cell cannot at the same time be carrying out a specific function and also undergoing active growth. He believes that on occasion some of these cells may abandon their “ habit of work " and assume a “ habit of growth, ” and this will lead to the development of a tumour.

Neither of the two latter explanations brings us very much nearer the solution of the question-they merely place the unknown factor one step farther back; but they serve to emphasize the biological aspect of the problem. At the present time the general weight of evidence seems to favour the idea that tumour formation is due to some intrinsic cause, whereby the normal processes of growth are disturbed, rather than to any extrinsic cause such as microbial infection. Therefore it is from a careful study of the laws of growth, and from research directed along broad biological lines that the best results are to be looked for in the future. Classification of Spontaneous Tumours.-So little is known as to the nature of these tumours that a satisfactory classification on a scientific basis is not yet within reach. The following is merely suggested as convenient:-

I.-Connective-tissue Tnmours.

Innocent. Malignant.

Liporna (fatty tumour).

Fibroma (fibrous tumour). Sarcoma.

Myoma (muscular tumour). Endothelioma.

Osteoma (bony tumour).

Chondroma (cartilaginous tumour).

Odontoma (tumour in connexion with teeth). Myxoma (mucoid tumour).

Neuroma (tumour in connexion with nerves). Glioma (neuroglial tumour).

Endothelioma (endothelial tumour).

Angioma (tumour composed of blood vessels). II.-Epithelial T umonrs.

I nnocent. M alignant.

Papilloma. Carcinoma.

Adenoma. Rodent Ulcer.

I. Connective-tissue Tnmonrsl-Lipoma (fig. 5).-Of the connective-tissue group the fatty tumours are the most common. They often arise from the layer of fat beneath the skin, and a usual site for these subcutaneous lipomata is the back of the trunk, though at times they are found on the limbs and elsewhere. They 1 Figs. 5, 6, 7, 8, 9, 14, 15 and 17 have been redrawn from Bland Sutton's Turnours, by permission; figs. 10, 11, 12 and 13 are from Rose & Carless, Surgery, by permission. V