While cancer of the lung has become much more prevalent in recent years, cancer of the mouth has not. Medical researchers have been puzzled by this, since cancer-causing agents, e.g., tobacco tar, reach the lungs through the mouth. In the Journal of the American Dental Association, investigators offer two tentative explanations: saliva has a protective effect, though whether this is brought about simply by washing away the cancer agent or by combating it chemically is not known; the tissues of the mouth are so constructed as to constitute a kind of "physiological barrier" against the entry of cancer agents.
Animal tests support...