Six out of eight epidermal papillomas, induced with tar in mice of homogeneous strain, have grown after transfer to the subcutaneous tissue of sucklings and weanlings. Five of them have been thus maintained for nearly or quite a year and a half, and in seven to nine successive groups of mice. The tumor studied longest has been kept going in five parallel lines since its primary implantation.

The papillomas have all grown progressively in most instances, and proved fatal. None has altered except through the occurrence of derivative cancers, but these have arisen so often as only to be excluded on transfer by a rigorous selection of grafts.

Histologically the papillomas have been of a single, completely unaggressive kind, yet transfer has disclosed great differences in their abilities. The tumors they form are of unique sorts. The cells of some are able-bodied (Type A), capable of spreading along bare connective tissue and keratinizing like normal, reparative epidermis. They line graft pockets, differentiate into the free space these provide, and form cysts densely packed with keratin. The papilloma is thus turned outside in. The cysts become huge as keratin accumulates in them, and eventually they rupture with result either in subcutaneous dissecting cysts or keratinizing surface growths that are often prodigious in size and fantastic in shape, but sometimes are completely like the cutaneous papillomas ordinarily induced by carcinogens, and tend, when small, to regress or come away as these frequently do. One growth of Type A was placed in the peritoneal cavity or in the liver, spleen or lung, and at all these situations it formed introverted cysts resembling the subcutaneous.

The cells of other papillomas are more or less crippled (Type C). In extreme instances they are unable to spread laterally, and produce relatively little keratin. They fail to line graft pockets, but their keratin inflames the exposed connective tissue, extravasation ensues, and a continually enlarging, fluid-filled cyst forms, with walls that are bare except where a stalked or cauliflower papilloma exists, projecting inwards. At last the cyst ruptures and a second dissecting cyst forms, also devoid of papilloma tissue; or else the overlying skin undergoes pressure necrosis, the cyst fluid escapes through a rent, and fatal infection ensues.

All gradations exist between Type A and Type C. The cancers derivative from both exhibit a marked disability,—though invasive they are almost or quite unable to extend along bare connective tissue. The papillomas that are possessed of this faculty spread beyond them along the cyst wall, and kill the host through their unceasing activity.

In collateral work a papilloma was transplanted that was found protruding from the external auditory canal of a mouse which had received an intramuscular injection of methylcholanthrene many months previously. The tumor is now in its 5th generation, after 15 months. The growths it forms are of Type A.

All of the papillomas are functioning tumors, with their own cells as the functioning product. Their papilliferous shape, when on the skin, is due solely to inability of their cells to gain space in other ways. Intrinsically they are keratomas.

The papillomas do well after transfer to deep situations because the growth of their cells is indirectly promoted, through favoring local conditions. No direct promotion takes place like that when the cells of prostatic and mammary tumors are stimulated to multiply by hormones. Doubtless many agents act in both ways, that is to say by dual promotion.

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