Mary Zanck, age 11, of Spokane, Wash., for her question:

HOW ARE TEARS PRODUCED?

Two lachrymal glands, one located in each eye, produce a secretion of tears that continually bathe the cornea of the eyeball. Tears help to clear out foreign particles, such as hair and dust, and also keep the eyes from drying out. Without tears the eyes would most certainly dry out and the result would be a loss of vision.

The glands are located behind the eyelids. With each blink of the eye, an additional amount of fluid is squeezed from the glands.

When people feel such emotions as grief, anger or sometimes great joy, the glands become tightened and squeeze out larger amounts of tears. And that's how we cry.

Tears are a salty solution that also contain substances that fight bacteria and infection.