s with
the intimate connection of the deep fascia with the periosteum over the
great trochanter, thus favouring invasion of the bone marrow when
permeation has spread thus far. He claims support for the permeation
theory from the fact that the humerus is rarely involved below the
insertion of the deltoid, and that spontaneous fracture of the femur is
three times more common on the side on which the breast cancer is
situated.

The tumour tissue may undergo necrosis, and when the overlying skin or
mucous membrane gives way an ulcer is formed. The margins of a
_cancerous ulcer_ (Fig. 57) are made up of tumour tissue which has not
broken down. Usually they are irregular, nodularly thickened or
indurated; sometimes they are raised and crater-like. The floor of the
ulcer is smooth and glazed, or occupied by necrosed tissue, and the
discharge is watery and blood-stained, and as a result of putrefactive
changes may become offensive. Haemorrhage is rarely a prominent feature,
but discharge of blood may constitute a symptom of considerable
diagnostic importance in cancer of internal organs such as the rectum,
the bladder, or the uterus.

[Illustration: FIG. 57.--Carcinoma of Breast with Cancerous Ulcer.]

_The Contagiousness of Cancer._--A limited number of cases are on record
in which a cancer appears to have been transferred by contact, as from
the lower to the upper lip, from one labium majus to the other, from the
tongue to the cheek, and from one vocal cord to the other; these being
all examples of cancer involving surfaces which are constantly or
frequently in contact. The transference of cancer from one human being
to another, whether by accident, as in the case of a surgeon wounding
his finger while operating for cancer, or by the deliberate introduction
of a portion of cancerous tumour into the tissues, has never been known
to occur. It is by no means infrequent, however, that when recurrence
takes place after an operation for the removal of cancer, the recurrent
nodules make their appearance in the main scar or in the scars of
stitches in its neighbourhood. In the lower animals the grafting of
cancer only succeeds in animals of the same species; for example, a
cancer taken from a mouse will not grow in the tissues of a rat, but
only in a mouse of the same variety as that from which the graft was
taken.

While cancer cannot be regarded as either contagious or infectious, it
is important to bear in mind the possibili