product of epithelial proliferation, and it has a vascular base. A true nail-horn usually appears clinically as a single tumor, while the inflammatory swelling, onychogryphosis, is a multiple affection attacking at the same time or in succession a number or all of the nails of both hands.

FIG. 64.-Onychogryphosis of toes; natural size (after Ziesing).

The inflammatory form of onychoma is extremely common in the toes of bedridden patients, especially old women and those who are filthy. The true onychoma occurs in persons in perfect health and under the best sanitary and hygienic conditions. The nail often reaches several inches in length and becomes curved, resembling a ram's horn. The writer removed a nail of this kind which was three inches in length. A recurrence of the tumor can be prevented with certainty only by extirpation of the whole matrix of the nail.

XIV. ADENOMA.

ADENOMA is a benign epithelial tumor which in structure resembles the glandular tissue of the organ in which the tumor is located. Adenoma is the second variety of benign tumors of the epiblast and the hypoblast. The relation of the epithelial cells to the basement membrane is the reverse of that of papilloma; that is, the basement membrane is on the outside of the parenchyma of the tumor, instead of on the inside, as is the case in papilloma. In papilloma of the cutaneous and mucous surfaces the cellular elements of the tumor often become detached and permanently lose their connection with the tumor; in adenoma the cells are confined in hollow spaces bounded by the basement membrane, and they or the unabsorbable products of their regressive metamorphoses remain permanently as a part of the tumor. These differences in the anatomical structure of the tumor will go far to explain why a papilloma never attains a large size, and why the size to which a rapidlyproliferating adenoma may attain is unlimited. In reference to the relation of the tumor-cells to the subcutaneous or submucous connective tissue, there exists a great analogy between papilloma, epithelioma, adenoma, and glandular carcinoma. An adenoma, as its name implies, is a glandular tumor. Broca included under the term "adenoma" all circumscribed glandular swellings. Cornil and Ranvier embraced in this class only glandular tumors composed of new glandular tissue. In the strictest etiological and pathological sense the term should be limited to glandular tumors containing adenomatous tissue produced from a tumor-matrix independently of the pre-existing glandular tissue. As adenoma is present in all the glandular organs, the cells of which it is composed resemble the type of cells of the gland or duct in which the tumor is located. Glandular tumors, however, are found in localities where glands do not normally exist. In such instances the tumor develops either from a matrix of embryonic cells displaced and isolated during fetal life-the so-called "rests "—or from a matrix of embryonic cells in a supernumerary or accessory gland. Such accessory glands are found in the vicinity of nearly all the glandular organs, notably the thyroid, pancreas, spleen, liver, kidneys, and mammary gland. Adenomata are found quite often in the

axillary space unconnected with the mammary gland. A fetal matrix in the vicinity of the umbilicus, derived from the intestinal tract, may give rise to adenomata representing intestinal glands. Tumors of this kind were observed by Küstner and Heukelem, and were freely supplied with unstriped muscular fibres. Glandular tumors springing from a post-natal matrix of embryonic cells are necessarily confined to normal or accessory glands.

FIG. 65.-Transverse section of follicles of large intestine of dog: the individual tubules are separated by the fibrous stroma of the mucosa (after Piersol).

The histological similarity between an adenoma and the normal tissues in which such a tumor may be located is well shown in Figures 65 and 66. The difference between an adenoma and normal gland-tissue, from a physiological standpoint, is best shown by tumors of glands in continuous physiological activity, such as the liver and the kidneys, from the absence of gland-ducts and the presence of an atypical in place of a typical circulation.

FIG. 66.-Polypus (adenoma) of rectum, showing the glands of the tumor; X 350 (after D. J. Hamilton): a, gland lined by columnar epithelium; b, stroma of the tumor.

Histology and Pathology.-The histogenesis of adenoma has been referred either to a congenital matrix of embryonic cells in glandular organs, accessory glands, or displaced islets of embryonic cells (heterotopic), or to embryonic cells of post-natal origin in glands and accessory glands. Like the papilloma, it receives its stroma and its bloodsupply from the mesoblast. The glandular part of a tumor remains in an adenoma permanently. The most important distinctive feature between a localized or diffuse hyperplasia of a gland and an adenoma.

is the absence of function in the latter in common with all other tumors. The absence of ducts prevents the escape of the products of cell-proliferation, frequently resulting in the formation of cysts the contents of which vary according to the nature of the degenerative processes which occur in the cells of the parenchyma of the tumor. Tumors in the interior of internal organs, as a rule, attain greater size than tumors of the cutaneous or the mucous surfaces. Adenoma of the breast seldom exceeds the size of a walnut. The essential structure of an

FIG. 67.-Adenoma of mammary gland; X 50 (after Karg and Schmorl): a, epithelial cells lining gland-space; b, glandular space; c, stroma.

adenoma is the stroma of fibrous or myxomatous connective tissue containing newly-formed glands of either the acinous or the tubular variety. A central space between the epithelial cells can invariably be found, representing the glandular spaces in normal glands.

Most of the myxomatous polypoid growths are glandular tumors. Adenoma containing tubular glands presents on section under the microscope the appearance of tubular glands. The cells are arranged in a single layer or in stratified layers; the centre of each tubule shows. a space toward which the unattached parts of the cells converge.

Adenoma composed of acinous glandular tissue shows on section under the microscope spaces lined by flat epithelial cells (Fig. 67). The stroma varies in amount: if abundant, the tumor is hard; if scanty, soft. The blood-vessels follow the stroma and supply each tubule or acinus of the tumor with an irregular network of capillary vessels. The cells of an adenoma are subject to fatty, mucoid, and colloid degeneration. The stroma frequently undergoes myxomatous degeneration. The progressive accumulation of the degenerated products of cell-proliferation leads to cyst-formation. Such cysts vary in size from microscopical spaces to cavities which contain many quarts of fluid. The largest cysts are found in, or in the vicinity of, the ovary. The fetal remains of ducts in the vicinity of the ovary give rise to the formation. of adenoma containing tubular structures the vegetative power of which is much greater than that of the Graafian follicles. The liability of an adenoma to become transformed into a glandular carcinoma is perhaps greater than that of papilloma. In fact, according to D. J. Hamilton, carcinoma is preceded by an adenomatous stage (Fig. 68), an opinion advanced years ago by Gouley of New York. The earliest evidences that such an occurrence has taken place are a more active multiplication of epithelial cells

and their migration through the basement membrane into the connective tissue outside the limits of the tumor (Fig. 68, b).

a

Etiology. The essential cause, the matrix of embryonic cells, has been referred to in the introductory remarks of this section. Of the exciting causes, trauma, irritation, and inflammation are the most influential. Adenomata are found most frequently in organs the seat of periodical congestion, such as the mammary and prostate glands, the uterus, and the ovaries. They are common also in mucous passages the seat of catarrhal affections, such as the nasal cavities and the rectum. Adenoma is met with most frequently in the young and in persons not beyond middle life. The greater frequency of adenoma of the ovary as compared

FIG. 68.-Development of a cancer of the mamma: a set of adenomatous acini becoming cancerous; X 350 (after D. J. Hamilton): a, an adenomatous swelling of an acinus; b, the cells of a similar swelling which have broken out and are invading the surrounding stroma; c, part which is cancerous.