A benign tumor that has its origin in canals, ducts, and follicles of glands which have become stopped up, causing a cyst (sac) to form that is filled with a perverted secretion. Sometimes the lining membranes of these little cavities take on an excessive growth and end in what are called simple tumors. Such tumors do no harm, except for their unsightliness, when developed on exposed parts of the body, or from size. The tissues of these tumors always resemble those of the structure from which they are built. They have no tendency to break through their retaining membrane, which, of course, was originally the lining membrane of the passage that became plugged up.

This is not true of epithelioma (a true cancer). This disease respects no restrictions; it breaks through and invades any tissue, spreads in all directions, and leaves destruction behind it.