acquire the activity of growth. The descendants of such cells
will become more and more undifferentiated, thereby developing an
increased vegetative activity.
Oertel finds an explanation of this want of complete cell-differentiation, loss of function, and acquired vegetative activity in the non-homogeneous character of the nuclear chromatin elements of the cell, and maintains that the different properties of the cell are carried and handed down by the different orders of chromatin loops. We have analogies to this in the two nuclei of some of the protozoa, the one being solely for the purpose of propagation, the other being associated with the functional activities of the cell. Oertel thinks that in man we have these two different functions carried on by the one nucleus containing both chromatin orders. If, from whatever cause, any of the chromatin loops belonging to the functional order be lost the descendants of such a cell, being unable to restore these loops, will be minus the functional attributes associated with the lost elements. These, having the full equipment of the vegetative order, will now develop the inherent power of proliferation to a greater or lesser extent.
The foregoing hypotheses have all sought the origin of new growths in some intrinsic cause which has altered the characters of the cell or cells which gave rise to them, but none of them explain the direct exciting cause. The parasitic hypothesis postulates the invasion of a parasite from without, thus making a new growth an infective process. Many cancer-parasites have been described in cancerous growths, including bacteria, yeasts and protozoa, but the innumerable attempts made to demonstrate the causal infective organism have all completely failed.
It is well known that cancer may develop in places where there has been chronic irritation; an example may be found in cancer of the tongue following on prolonged irritation from a jagged tooth. Clay-pipes may also give rise to cancer of lips in males in England, while cancer of the mouth of both sexes is common in India where chewing a mixture of betel leaves, areca-nut, tobacco and slaked lime is the usual practice. In the case of the squamous epithelial cancer of the anterior abdominal wall found so frequently in the natives of Kashmir, the position of the cancer is peculiar to this people, and is due to the chronic irritation following on repeated burns from using the “kangri”—a small earthenware vessel containing a charcoal fire enclosed in basket-work, and suspended round the waist, to assist in maintaining warmth in the extreme cold of the hills of Kashmir.
The irritant may be chemical, as is seen in the skin cancers that develop in workers in paraffin, petroleum, arsenic and aniline. However close the relationship is between chronic irritation and the starting of cancer, we are not in a position to say that irritation, physical or chemical, by itself can give rise to new growths. It may merely act locally in some way, and so render that part susceptible to unknown tissue stimuli which impart to the cells that extraordinary power of proliferation characteristic of new growth.
At the present time we are quite uncertain what is the ultimate cause of new growths; in all probability there may be one or more aetiological factors at play disturbing that perfect condition of equilibrium of normal tissues. A defect in co-ordination allows the stimulated active vegetative cellular elements, or the more fully differentiated tissue, to over-develop and so form tumours, simple or malignant.
Other Tissue Products
Mucoid.—In many pathological conditions we have degenerative products of various kinds formed in the tissues. These substances may be formed in the cells and given out as a secretion, or they may be formed by an intercellular transformation. In the mucinoid conditions, usually termed “mucoid” and “colloid” degenerations, we have closely allied substances which, like the normal mucins of the body, belong to the glucoproteids, and have in common similar physical characters. There is neither any absolute difference nor a constancy in their chemical reactions, and there can be brought about a transition of the “colloid” material into the “mucoid,” or conversely. By mucoid is understood a soft gelatinous substance containing mucin, or pseudomucin, which is normally secreted by the epithelial cells of both the mucous membranes and glands. In certain pathological conditions an excessive formation and discharge of such material is usually associated with catarrhal changes in the epithelium. The desquamated cells containing this jelly-like substance become disorganized and blend with the secretion. Should this take place into a closed gland space it will give rise to cysts, which may attain a great size, as is seen in the ovarian adenomata. In some of the adenoid cancers of the alimentary tract this mucoid material is formed by the epithelial cells from which it flows out and infiltrates the surrounding tissues; both the cells and tissues appear to be transformed into this gelatinous substance, forming the so-called “colloid cancer” (fig. 42, Pl. IV.).
The connective tissue is supplied normally with a certain amount of these mucinoid substances, no doubt acting as a lubricant. In many pathological conditions this tissue is commonly found to undergo mucoid or myxomatous degeneration, which is regarded as a reversion to a closely similar type—that of foetal connective tissue (fig. 43, Pl. IV). These changes are found in senile wasting, in metaplasia of cartilage, in many tumours, especially mixed growths of the parotid gland and testicle, and in various inflammatory granulation ulcers. In the wasting of the thyroid gland in myxoedema, or when the gland is completely removed by operation, myxomatous areas are found in the subcutaneous tissue of the skin, nerve-sheaths, &c.
Colloid.—This term is usually applied to a semi-solid substance of homogeneous and gelatinous consistence, which results partly from excretion and partly from degeneration of cellular structures, more particularly of the epithelial type. These cells become swollen by this translucent substance and are thrown off into the space where they become fused together, forming colloid masses. This substance differs from the mucins by being precipitated by tannic acid but not by acetic acid, and being endowed with a higher proportion of sulphur.
In the normal thyroid there is formed and stored up in the spaces this colloid material. The enlarged cystic goitres show, in the distended vesicles, an abnormal formation and retention of this substance (fig. 44, Pl. V.). Its character is readily changed by the abnormal activities which take place in these glands during some of the acute fevers; the semi-solid consistence may become mucoid or even fluid.
Serous degeneration is met with in epithelial cells in inflammatory conditions and following on burns. The vitality of these cells being altered there is imbibition and accumulation of watery fluid in their cytoplasm, causing swelling and vacuolation of the cells. The bursting of several of these altered cells is the method by which the skin vesicles are formed in certain conditions.
Glycogen is formed by the action of a ferment on the carbohydrates—the starches being converted into sugars. The sugars are taken up from the circulation and stored in a less soluble form—known as “animal starch”—in the liver and muscle cells; they play an important part in the normal metabolism of the body. The significance of glycogen in large amounts, or of its absence from the tissues in pathological conditions, is not clearly understood. It is said to be increased in saccharine diabetes and to be greatly diminished in starvation and wasting diseases.
Fat.—Fatty accumulations in the tissues of the body are found in health and in pathological conditions; these are usually recognized and described as fatty infiltrations and fatty degenerations, but there are intermediate conditions which make it difficult to separate sharply these processes.
The fatty accumulations known as infiltrations (figs. 45 and 46, Pl. V.) are undoubtedly the result of excessive ingestion of food material containing more neutral fats than the normal tissues can oxidize, or these, as a result of defective removal owing to enfeebled oxidative capacities on the part of the tissues, become stored up in the tissues.
In acute and chronic alcoholism, in phthisis, and in other diseases this fatty condition may be very extreme, and is commonly found in association with other tissue changes, so that probably we should look on these changes as a degeneration.
Adiposity or obesity occurs when we have an excessive amount of fat stored in the normal connective-tissue areas of adipose tissue. It may be caused by various conditions, e.g. over-nutrition with lack of muscular energy, beer-drinking, castration, lactation, disturbed metabolism, some forms of insanity, and may follow on some fevers.
Fatty degeneration is a retrogressive change associated with the deposit of fatty granules or globules in the cytoplasm, and is caused by disorganized cellular activity (figs. 26 and 27, Pl. II.). It is frequently found associated with, or as a sequel to, cloudy swelling in intense or prolonged toxic conditions. Over and above the bacterial intoxications we have a very extreme degree of fatty degeneration, widely distributed throughout the tissues,
