of reproductive activity than in the later
years of life; rectal cancer is not infrequently met with during the
second and third decades. There is evidence that the irritation caused
by alcohol and tobacco plays a part in the causation of cancer, in the
fact that a large proportion of those who become the subjects of cancer
of the mouth are excessive drinkers and smokers.

A cancer may appear as a papillary growth on a mucous or a skin surface,
as a nodule in the substance of an organ, or as a diffuse thickening of
a tubular organ such as the stomach or intestine. The absence of
definition in cancerous tumours explains the difficulty of completely
removing them by surgical measures, and has led to the practice of
complete extirpation of cancerous organs wherever this is possible. The
boundaries of the affected organ, moreover, are frequently transgressed
by the disease, and the epithelial infiltration implicates the
surrounding parts. In cancer of the breast, for example, the disease
often extends to the adjacent skin, fat, and muscle; in cancer of the
lip or tongue, to the mandible; in cancer of the uterus or intestine, to
the investing peritoneum.

In addition to its tendency to infiltrate adjacent tissues and organs,
cancer is also liable to give rise to _secondary growths_. These are
most often met with in the nearest lymph glands; those in the neck, for
example, becoming infected from cancer of the lip, tongue, or throat;
those in the axilla, from cancer of the breast; those along the
curvatures of the stomach, from cancer of the pylorus; and those in the
groin, from cancer of the external genitals. In lymph vessels the cancer
cells may merely accumulate so as to fill the lumen and form indurated
cords, or they may proliferate and give rise to secondary nodules along
the course of the vessels. When the lymphatic network in the skin is
diffusely infected, the appearance is either that of a multitude of
secondary nodules or of a diffuse thickening, so that the skin comes to
resemble coarse leather. On the wall of the chest this condition is
known as _cancer en cuirasse_. Although the cancer cells constantly
attack the walls of the adjacent veins and spread into their interior at
a comparatively early period, secondary growths due to dissemination by
the blood-stream rarely show themselves clinically until late in the
course of the disease. It is probable that many of the cancer cells
which are carried away in the bl