the physical properties, or the nature (whether destructive or harmless) of various forms. Virchow offered a classification based on the histology (histogenetic classification); others have grouped tumors according to the embryologic derivation of the tissues from which the new-growths originate or of the tissue composing the tumor. It is perhaps wisest to attempt no classification of any kind, and in the following sections I have arranged the various tumors according to their histologic characters without attempting to establish groups.

FIBROMA.

Definition. A fibroma is a tumor composed of connectivetissue cells and fibers resembling those seen in fibrillar tissue.

Etiology. The causes of fibroma are as obscure as are those of tumors in general. There are many facts, however, which point to the importance of irritation or injury as exciting causes. Among these may be mentioned the development of a peculiar form (keloids) in scar-tissue and the resemblance of these tumors to spontaneous fibromata, and the appearance of fibrous nodules in the skin at points of friction or definite pressure or in places irritated by discharges.

It is impossible to draw sharp lines between fibromata and hyperplasias of connective tissue following irritation. In the skin and superficial tissues there occur hyperplastic connectivetissue processes, constituting elephantiasis, which in some cases are distinctly the result of irritation and in other cases seem purely spontaneous. The elephantiasis of tropical countries, often due to occlusion of the lymphatic channels by filariæ, and the thickening of the skin and adjacent connective tissue of the legs around old ulcerations or eczematous areas, are instances in which distinct irritation is the cause. On the other hand, congenital elephantoid conditions of the skin are seemingly spontaneous or causeless, and some of the cases in later life have the same characteristic. The diffuse hyperplasias of the viscera, though often distinctly inflammatory, may appear without adequate discoverable cause, and, according to the view of some authorities, are to be looked upon as diffuse fibrosis or fibromatosis, rather than as inflammatory conditions. In ordinary cases of cirrhosis of the organs the connective-tissue growth is entirely diffuse, but thickenings may occur in certain situations, and the resemblance to tumor-formation is then much more striking. This is sometimes the case in the liver, but particularly in the kidneys. In the breast there are cases in which no dividing-line can be drawn between chronic interstitial mastitis and fibroma. The microscopic appearances are practically identical. A distinction, if any can be made, is based upon the nodular character and spontaneous origin in the one and the opposite conditions in the other.

Appearance. The naked-eye appearance of fibromata is usually quite characteristic. The tumor may be hard (Fig. 38)

FIG. 38.--Hard fibroma (Warren).

or soft (Fig. 39), according as it resembles loose or dense connective tissue in structure and according to the amount of

edematous liquid or associated myxomatous degeneration of the intercellular substance. The growth is more or less rounded and usually enclosed in a distinct capsule. In the substance of organs it is spherical or tuberous, and when near the surface projects more or less. When it springs from a mucous or serous membrane or from the skin the weight of the tumor may gradually lead to a polypoid formation. Some of the fibromata of the skin are arborescent or dendritic in form, and keloids are frequently irregular or star-like in outline. The rounded and encapsulated tumors may be lobulated, though more frequently they occur in a uniform

mass.

Seats. The points of origin from which fibroid tumors arise

are very numerous, though they always spring from pre-existing connective tissue. Among some of the more common localities may be mentioned the subcutaneous connective tissue, the submucous tissue, the periosteum of bones, tendons and tendonsheaths, and the fibrous covering of nerves. Of the internal organs, the uterus, the ovaries, the kidneys, and heart-muscle are the most important. Less frequently fibromata are found in the serous membranes of the chest and abdomen or of the central nervous system. The fibroids of the skin, the uterus, the nerves (see Neuroma), and the mucous membrane of the nose are the most important.

The mammary gland presents several interesting forms of inflammatory or fibromatous new-growth. First, there is a diffuse form of interstitial mastitis in which the entire breast becomes indurated; this is distinctly inflammatory. In other cases nodular or lobular areas of thickening occur, and in these the evidences of

inflammatory action are sometimes obscure or wholly wanting. Some of these are certainly instances of true fibroma (fibroma mamma nodulum). In still another group of cases the fibromatous proliferation of the connective tissue projects into the tubules and acini of the gland, pushing the epithelium before it and sometimes sprouting or proliferating in polypoid form within the tubules. The gland in such cases may present a striking macroscopic appearance on section. Numerous cystic formations may be visible with projecting dendritic formations within, causing an appearance somewhat like that of a section through a cauliflower (Fig. 40). Microscopically the proliferations of the connective tissue between the tubules and projecting within the tubules constitute the characteristic features. The term intracanalicular fibroma has been given to such cases. Obstruction of the tubules in certain.

areas may lead to very marked cystic distention. Combinations with sarcoma are frequent.

Structure. The definition explains the structure of fibromata. On section through the body of the tumor the fibrous nature may be revealed by a distinct concentric or radiating striation, particularly in the case of hard fibromata. The softer varieties are much less likely to present this feature. The color is usually gray or whitish, and may be glistening when there is mucous degeneration, or yellow in the case of associated lipoma. Microscopically a striking feature is the connective-tissue cell, which is star-like and branching in the softer tumors, and compressed, spindle-shaped, or elongated in the case of the hard varieties. The intercellular substance is composed of a fibrillar network and homogeneous or granular material traversed by thinwalled blood-vessels, ofttimes having merely an endothelial coat. Cavernous dilatation and rupture of the vessels may cause a distinct hemorrhagic appearance of the section; but such conditions

are rare.

In some cases embryonal round cells may be abundant and a distinct sarcomatous transformation of the tumor may occur. This, however, is rare. In other instances, as has already been remarked, myxomatous tissue may be conspicuous, and all grades of transformation from a pure fibroma to a pure myxoma may be met with, especially in the case of soft fibroma. Fatty degeneration of the cells and lipomatous infiltration or associated lipoma. are also frequent. These forms, the myxomatous and lipomatous, are particularly frequent in the submucous and subcutaneous connective tissues. Calcareous degeneration occurs in large fibromatous tumors, particularly in those of the uterus, and very rarely true ossification has been reported. Less commonly association of fibroma with other forms of tumor-growth is found. Among these the combination of fibroma with leiomyoma is usual in the

uterus.

Nature. Fibroma is essentially a benign tumor, though recurrence occasionally takes place after removal, this being particularly the case with keloids and some of the polypoid growths of mucous membranes. In some of these instances there is undoubtedly a resemblance to sarcoma, if not actual sarcomatous transformation. As a rule, fibroid tumors are destructive only in so far as they are capable of producing mechanical injury by pressure. The growth of the tumors is usually exceedingly slow.

MYXOMA.

Definition. Myxoma is a tumor composed of connectivetissue cells and an intercellular substance containing mucoid material in more or less abundance. The gelatinous substance of

Wharton in the umbilical cord and the vitreous humor of the eye are normal types which myxomata resemble in their structure.

Etiology. The causes and the nature of myxomata are practically the same as those of fibroma, and intermediate forms make it difficult to draw a sharp line between the two.

Appearance.-A typical myxoma is a soft, more or less flabby growth enclosed by a capsule, and having a rounded outline. It may project from the surface of the body or of an organ as a hemispherical elevation, or may hang by a narrowed pedicle in the form of a distinct polyp. The latter is frequent in the mucous membranes, but may occur in the skin as well. Sometimes the tumor is lobulated, and the lobules may be visible or may be easily felt. Occasionally lipomatous growths are diffuse, having no capsule and marked by no definite limits.

Seats. Among the common situations are the subcutaneous and submucous tissues and the connective tissues of certain organs, notably the mammary glands. They may occur along the course of nerves, in the brain or the spinal cord. The tumor may be

solitary, or, like fibroma, may be met with in numbers. Congenital myxoma has frequently been found.

Structure.-Microscopically the characteristic features are stellate or spindle-shaped connective-tissue cells which lie within a matrix of myxomatous material (Fig. 41). The latter is homogeneous or slightly granular, and somewhat refractive to the light, giving the surface a glistening quality. The cells themselves may be entirely normal young connective-tissue cells, or they may present evidences of fatty degeneration. Round granulation-tissue cells are met with in some instances, either scattered through the tumor or in certain areas, and may be so abundant as to justify the term