While cancer cannot be regarded as either contagious or infectious, it is important to bear in mind the possibility of infection of a wound with cancer when operating for the disease.  A cancer should not be cut into unless this is essential for purposes of diagnosis, and the wound made for exploration should be tightly closed by stitches before the curative operation is proceeded with; the instruments used for the exploration must not be used again until they have been boiled.  The greatest care should be taken that a cancer which has softened or broken down is not opened into during the operation.

Investigations regarding the cause of cancer have been prosecuted with great energy during recent years, but as yet without positive result.  It is recognised that there are a number of conditions which favour the development of cancer, such as prolonged irritation, and a considerable number of cases have been recorded in which cancer of the skin of the hands has followed prolonged and repeated exposure to the Rontgen rays.

The Alleged Increase of Cancer.—­Regarding the alleged increase of cancer, it may be pointed out that it is impossible to ascertain how much of the apparent increase is due to more accurate diagnosis and improved registration.  It is probable also that some increase has taken place in consequence of the increased average duration of life; a larger proportion of persons now reach the age at which cancer is frequent.

The prognosis largely depends on the variety of cancer and on its situation.  Certain varieties—­such as the atrophic cancer of the breast which occurs in old people, and some forms of cancer in the rectum—­are so indolent in their progress that they can scarcely be said to shorten life; while others—­such as the softer varieties of mammary cancer occurring in young women—­are among the most malignant of tumours.  The mode in which cancer causes death depends to a large extent upon its situation.  In the gullet, for example, it usually causes death by starvation; in the larynx or thyreoid, by suffocation; in the intestine, by obstruction of the bowels; in the uterus, prostate, and bladder, by haemorrhage or by implication of the ureters and kidneys.  Independently of their situation, however, cancers frequently cause death by giving rise to a progressive impairment of health known as the cancerous cachexia, a condition which is due to the continued absorption of poisonous products from the tumour.  The patient loses appetite, becomes emaciated, pale, and feverish, and gradually loses strength until he dies.  In many cases, especially those in which ulceration has occurred, the addition of pyogenic infection may also be concerned in the failure of health.