Monica Nelson, age 13, of Camden, N.J., for her question:

WHAT CAUSES RHEUMATISM?

Rheumatism is any painful condition that involves the muscles, joints or connective tissues such as tendons and ligaments. The word comes from the Greek word "rheumatismos," meaning a "flowing of mucus."

Doctors have found that changes in character of the mucus in body tissues is responsible for many rheumatic diseases.

Muscular rheumatism is probably one of the most common forms. It involves the muscles rather than the joints of the body. The muscle stiffness that occurs during influenza or colds, or when a person's arms or legs have been overstrained, are types of muscular rheumatism.

Wryneck, or a stiff neck, and lumbago are other common forms of rheumatism.

Rheumatic fever is a kind of rheumatism that particularly affects young people. Other kinds of rheumatism include arthritis, in which the joints become inflamed and swollen, and bursitis, an inflammation of the lubricating spaces near the joints.