inate in a
pigmented mole which has been subjected to irritation. The primary
growth may remain so small that its presence is not even suspected, or
it may increase in size, ulcerate, and fungate. The amount of pigment
varies: when small in amount the growth is brown, when abundant it is a
deep black. The most remarkable feature is the rapidity with which the
disease becomes disseminated along the lymphatics, the first evidence of
which is an enlargement of the lymph glands. As the primary growth is
often situated on the sole of the foot or in the matrix of the nail of
the great toe, the femoral and inguinal glands become enlarged in
succession, forming tumours much larger than the primary growth.
Sometimes the dissemination involves the lymph vessels of the limb,
forming a series of indurated pigmented cords and nodules (Fig. 104).
Lastly, the dissemination may be universal throughout the body, and this
usually occurs at a comparatively early stage. The secondary growths are
deeply pigmented, being usually of a coal-black colour, and melanin
pigment may be present in the urine. When recurrence takes place in or
near the scar left by the operation, the cancer nodules are not
necessarily pigmented.

[Illustration: FIG. 104.--Diffuse Melanotic Cancer of Lymphatics of Skin
secondary to a Growth in the Sole of the Foot.]

To extirpate the disease it is necessary to excise the tumour, with a
zone of healthy skin around it and a somewhat large zone of the
underlying subcutaneous tissue and deep fascia. Hogarth Pringle
recommends that a broad strip of subcutaneous fascia up to and including
the nearest anatomical group of glands should be removed with the tumour
in one continuous piece.

#Secondary Cancer of the Skin.#--Cancer may spread to the skin from a
subjacent growth by direct continuity or by way of the lymphatics. Both
of these processes are so well illustrated in cases of mammary cancer
that they will be described in relation to that disease.

#Sarcoma# of various types is met with in the skin. The fibroma, after
excision, may recur as a fibro-sarcoma. The alveolar sarcoma commences
as a hard lump and increases in size until the epidermis gives way and
an ulcer is formed.

[Illustration: FIG. 105.--Melanotic Cancer of Forehead with Metastases
in Lymph Vessels and Glands.

(Mr. D. P. D. Wilkie's case.)]

A number of fresh tumours may spring up around the original growth.
Sometimes the primary growth appears in