a more frequent starting-point of a carcinoma than of a sarcoma. The deepest stratum of epithelial cells is composed of young cells which are in touch with the membrana propria, which, so long as the tumor remains benign, constitutes an impermeable partition between the essential tumor-elements and its stroma, the subcutaneous or submucous connective tissue. If, in consequence of prolonged irritation or other exciting causes, this partition is damaged, the embryonic cells have access to the vascular part of the tumor, and, once there, the transformation from a papilloma into a carcinoma takes place. If, on the contrary, fetal "rests" or post-natal embryonic cells in the connectivetissue part of the tumor become environed by causes favoring tumorgrowth, the papilloma is transformed into a sarcoma. Such a transformation was observed by Simon in a papillary growth of a joint. Sarcoma of the skin has occasionally a similar origin.

Topography.-Papilloma is met with in various parts of the body, but some parts are more predisposed to it than others. It is most frequent in localities most exposed to irritation. We shall not include papilloma of an infective origin-as warts, condylomata, and molluscum contagiosum, all of which are inflammatory swellings and not true tumors in the discussion of the topographical distribution of papilloma. Warts (verruca) come and disappear mysteriously. They increase in size much more rapidly than papilloma, and they often disappear spontaneously. Condyloma, another papillomatous inflammatory swelling resembling in its structure papilloma, almost always appears multiple in places where skin and mucous membrane meet and are bathed with infective discharges, usually of a gonorrheal origin. The vulva, the prepuce, and the anal region are the parts most frequently affected by condyloma. The removal of the primary causes usually results in a speedy cure. Molluscum (Bateman) or epithelioma contagiosum (Virchow) is now generally recognized as an inflammatory swelling. Its contagiousness is the best possible evidence that it is not a tumor. Haab succeeded in producing it artificially in animals by inoculation. Austrian and English dermatologists have traced its starting-point to sebaceous glands. The papillary growths of non-infective origin, the true benign epithelial tumors, do not disappear spontaneously; their growth is limited by an inherent limitation of tissue-proliferation or by degenerative changes. These tumors have a very wide distribution, and the more important localities inhabited by them, and the different clinical varieties, will now be discussed.

Skin.-Papilloma of the skin occurs in two principal forms: 1. Cornu cutaneum; 2. Fibrous papilloma. In the former variety the tumor is composed almost exclusively of epiblastic tissue; in the latter

the connective tissue derived from the mesoblast is present in varying proportions.

Cornu Cutaneum.-The cutaneous horn represents a form of papilloma in which the tumor is composed almost exclusively of desiccated epithelial cells corresponding with the horny layer of the skin. The old cells, instead of becoming desquamated, remain attached to the tumor-matrix, forming projections varying in length from half an inch to twelve or more inches. Such horns are found most frequently on the scalp, temple, forehead, eyelid, nose, lip, cheek, shoulder, arm, elbow, thigh, leg, knee, toe, axilla, thorax, buttock, loin, penis (Fig. 56),

and scrotum. The matrix of such tumors is very vascular. Horny tumors of the skin can readily be enucleated, and they seldom return after removal. A post-natal matrix for cutaneous horns is furnished most frequently by scars. Cruveilhier described a specimen of cornu cutaneum which originated from a scar following a burn of the forearm, the tumor reaching such an enormous size that amputation became necessary (Fig. 57). The tumors in this case were multiple.

That desiccation is not the sole cause in the production and fixation of such an enormous mass of epithelial cells is shown by the fact that papillomata of a similar structure are occasionally found in dermoid

and sebaceous cysts. The matrix of a cutaneous horn undoubtedly not only possesses the inherent capacity of producing epithelial cells very rapidly, but also furnishes the cement-substance which fixes the old epithelial cells, thus preventing their removal by desquamation. There is no reason why papillomata should not develop as secondary formations in epithelial tumors of either a benign or a malignant type.

FIG. 57.-Cornua cutanea from the scar of a burn (after Cruveilhier).

Not infrequently we find in the interior of an adenoma, a cystoma, or a carcinoma papillary growths which resemble in every respect the surface papillomata, and which impart to the tumor additional pathological and clinical characteristics. Papillomatous cysts of the ovary (Fig. 58) are regarded with special interest by the surgeon. A semi-malignant nature was assigned to them long ago. There can be no doubt that in many instances such tumors are malignant from the beginning, but in other instances the papillomata are benign and remain so. The desquamated epithelial cells furnish here a part of the contents of the

cysts (Fig. 58, d). As in surface tumors, the epithelial cells are stratified. Tumors of large size are formed by the aggregation and coalescence of numerous smaller tumors.

The fibrous papillomata of the skin occupy most frequently the region

FIG. 58. Papillomatous cyst of ovary; X 110 (Surgical Clinic, Rush Medical College, Chicago): a, interpapillary space; b, stroma; c, epithelial lining; d, amorphous, non-staining detritus with a few detached epithelial cells; e, proliferating areas.

of the face, scalp, and hands; they are of slow growth and never attain large size.

Respiratory Organs.-The larynx is the most frequent seat of papillomata. Morgagni's pockets are their favorite locations. They appear as isolated affections or as multiple tumors closely aggregated, giving to the mass a cauliflower-like appearance. The symptoms will vary according to the size and the location of the tumor. Hoarseness, cough harassing in character, and difficult breathing alternating with temporary attacks of dyspnea, are some of the leading clinical features. Not infrequently, papilloma of the larynx undergoes transformation into carcinoma, as was probably the case in the instance referred to in the section treating of the Transformation of Benign into Malignant Tumors.

Digestive Tract.-The mucous membrane of the cavity of the mouth is derived from the epiblast and is frequently the seat of papilloma. The favorite localities are the mucous membrane of the cheek, the prolabium of the lip, the tongue, the soft palate, and the pharynx. The naso-pharyngeal space is frequently studded with papillomatous vegetations. The stomach is almost exempt from this affection. The frequency with which the mucous membrane of the intestinal canal is affected increases in a downward direction. Papillomata are rare in the intestines, while in the rectum they are most frequent, and are either

sessile or pedunculated, constituting a frequent form of polypus of this organ. The writer has repeatedly seen the mucous membrane of the lower part of the rectum studded with papillary tumors varying in size from a hempseed to a cherry (Fig.

59). The symptoms which attend this affection of the rectum are hemorrhage, usually slight, tenesmus, and a glairy discharge.

Urinary Organs.-The urinary tract is very often the seat of papilloma, and no part of it is exempt. Papillomata are frequently located in the urethra, and especially around the margin of the meatus in the female. In this locality they are often multiple, and they are a source of great distress to the patient. The tumors are very vascular, are extremely sensitive to touch, and are the source of great pain during micturition. Papillomata of the male urethra are more frequent than was formerly supposed, and their presence can now be ascertained and their removal be facilitated by the use of the urethroscope. They simulate, and have usually been mistaken for, stricture.

FIG. 59.-Papilloma of the rectum (after Lücke): a, submucous connective tissue; b, papillæ, some of them branching, covered by columnar epithelia.

Papilloma of the bladder is a frequent affection of this organ. The connective tissue is usually abundant and carries with it one or more vessels of considerable size. The main stem of the tumor usually gives off branches which in turn again become branched, giving to the tumor an arborescent structure (Fig. 60). As the connective-tissue core of the tumor is often covered by only one layer of epithelial cells, and the ultimate branches are often exceedingly delicate, it is easy to understand that such tumors frequently give rise to hemorrhage. If the principal artery of such a tumor is eroded or torn, the hemorrhage may become alarming and even fatal. Sometimes small fragments of such a tumor are voided with the urine or are removed in the eye of the catheter, affording the surgeon an opportunity to make a correct diagnosis, by the aid of the microscope, in what was before an obscure case. The cystoscope renders valuable assistance in ascertaining not only the existence, but also the exact location and character, of the tumor. The liability of such growths to become transformed into malignant tumors is well known and generally recognized. A very interesting case of papillomatous tumors of the pelvis of the kidney is reported by Murchison