The heteroplasy, viz., normal epithelial cells in the wrong place, infiltrating the connective tissues of the parenchyma of the derma, or of the glands constitutes the essence of the cutaneous cancer, or epithelioma. It belongs to the class of the malignant growths on account of the persistent ulceration, of the tendency to recur after removal, of the infection which it produces in the tissues of the adjacent parts of the skin, and on account of the reproduction in the lymph-glands communicating with the lymphatic vessels of the affected part. It is not my object to develop the doctrine of cancers, which could not be done in the limits of a brief address, but I will only dwell on the nature of the cutaneous cancers and on their treatment.
Thiersch, in his remarkable work, published in 1865, on the epithelial cancers of the skin, distinguished two varieties from a topographical standpoint,