Aletha Dorak, age 13, of Poughkeepsie, N.Y. for her question:

WHY IS THE INSIDE OF THE MOUTH ALWAYS WET?

We use the mouth for chewing, sucking, swallowing, speaking and respiration. The entire mouth cavity is lined with mucous membranes.

The inside of the mouth is always wet because the mucous membranes continually secret a fluid called mucus. The main purpose of mucus is to lubricate the passages and also to protect the membrane from irritation by foreign matter and the foods we eat.

A thick mucus lubricates some parts of the body, such as the nose, but a thinner mucus lubricates the saliva glands and protects the mouth, esophagus and other passages of the alimentary or digestive tract from irritation by various foods, bacteria and foreign particles that are swallowed.

Moisture also comes from the salivary glands in the walls of the mouth.