was covered by a blood-stained scab. The tumour was partially excised under ether and the deeper portions used for transplantation. The superficial part with the adjacent skin was preserved for histological examination. Microscopical examination of sections made perpendicularly to the surface through the centre of this portion shows (figs. 19 & 20) that the growth is connected with the skin. Under the scab the surface epithelium dips down into a depression lined by squamous epithelium and from the deeper surface of this cavity irregular processes proceed in the form of alveoli with central keratinisation. Elsewhere the tumour parenchyma is purely alveolar without keratinisation and at another part close under the skin to one side of the central cavity it presents an adenomatous or adeno-carcinomatous structure (figs. 20 & 22). At one part the preparations show the alveoli of squamous epithelium adjoining an adenomatous area (fig. 21). A metastasis in the lung consists of a spherical mass of closely packed alveoli of polygonal cells in which at several points very perfect keratinisation has taken place (fig. 23). The conclusion to be drawn from these appearances is that the growth is a squamous-cell carcinoma, probably of the region of the nipple. The acinous structure of one part of the tumour is probably only an expression of the tendency which epithelial cells show to arrange themselves as a lining to spaces in which they lie, in this case in the lacunæ of the connective tissue. Ribbert has shown that a similar condition leads to the formation of small cysts lined in the first place by a single layer of cells when normal skin is transplanted into the subcutaneous tissue of the rabbit, an observation we have been able to confirm in the mouse. The cyst-like alveoli of the tumour (28) referred to in the preceding paragraph, the subperitoneal cysts of the epithelioma of the stomach (fig. 5), and analogous formations observed in epitheliomata of man, have probably the same significance. This tumour is referred to as in the tabular summary, and its behaviour on transplantation forms the subject of a separate paper at a later page.

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SQUAMOUS-CELLED CARCINOMA OF NIPPLE.

A small elevated disc-shaped tumour nearly 1 cm. in diameter appeared in the region of the left axillary nipple of a mouse (8) from

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which a hæmorrhagic adeno-carcinoma had been removed from the right side of the vulva three months before. The growth is connected with

[To face p. 82.

R. Muir, del. FIG. 19.-Mouse. Squamous-cell carcinoma of axilla: vertical section through superficial part of primary growth showing small cyst filled with masses of keralin, and connection of the epithelium lining it with the skin above and the tumour pacenchy na below.

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FIG. 20.-Mouse. Squamous-cell carcinoma of axilla: higher power view of margins of the growth. Shows also adenomatous structure of the tumour under the skin to the left side.

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