Debbie Berquist, age 12, of Santa Maria, California, for her question:

How do our eyes form tears?

Tears are made of a salty moisture which has a far more important function than crying. In fact, it must be on the job all day and every day to keep the eyes clean and shiny bright. But when your heart breaks with sadness, with pain or tragedy, this moisture is ready to work overtime. It supplies the deluge of tears that streams doom the cheeks, blurs the eyes and clogs the nose with sniffles.

Tears are manufactured by two small glands, about the same size and somewhat the same shape as an almond. One is situated in each eye, under the upper eyelid near the outside corner. Tears consist of the gentle fluids that bathe the living cells inside the body. These fluids are soothing solutions that contain dissolved chemicals. This mixture is a delicate balance of salts and other chemicals.

Lachrymal is an old, sweet sounding name for tears. Scientists used it to name several items in the body's tear system. The two little factories that manufacture this moisture are called the lacrimal glands; thus, tears are called lacrimal fluid. However, weeping is not the main job of the lacrimal fluid, but rather it works to cleanse the surface of the eyes. It keeps their delicate surfaces moist and washes away fine dust particles. Some of its ingredients even fight bacteria, and others provide proteins to help the eyes resist infection.

The lacrimal system is neatly arranged to keep this wonderful fluid working through all of our waking hours. The eyelids perform a double duty. Without our noticing it, they blink on schedule  ¬about once every six seconds. Each blink moves muscles around the lacrimal glands, squeezing out a little moisture. The blinking eyelids also work somewhat like natural windshield wipers, spreading the lacrimal fluid over the delicate surface of the eyes.

This requires only a little moisture, but there must be some way to dispose of the used fluid. The "garbage disposals" are small openings, one at the inner corner of each eye. These are the lacrimal ducts which drain the used fluid out through a tube at the back of the nose. This soothing, washing and draining occurs every time we blink. However, when we feel strong emotions, certain muscles contract causing the lacrimal glands to squeeze out extra fluid    too much to drain away through the usual channels. It fills the eyes, spills over and floods down the face in streams of weeping tears.

Laughter, like crying, may squeeze out extra lacrimal fluid and start a flood of tears. In any case, the deluge is soon over and no harm is done. When the flow of tears diminishes, the lacrimal system quickly returns to its normal eye washing duties.