Lynne Kenney, age 13, of Libertyville, I11., for the question:

EXACTLY WHAT ARE TEARS?

Tears are made of a salty moisture that spills out from the eyes and streams down the cheeks. But this is not the whole story. Tears are not only for crying or laughing. They are much more than just salty liquid, and their main duty keeps them busy all day long.

The air is full of dusty particles, and the surface of the eyes must be kept clean. Eyes are bright and shiny because they are continuously washed and wiped as we blink, about once every six seconds. The blinking eyelids act like automatic windshield wipers  and the cleansing lotion is the same teary liquid that spills down the cheeks during a crying spell.

This remarkable moisture is manufactured in the tear glands. These are the size and shape of almonds. One is situated under the lid at the outside corner of each eye. The watery fluid they manufacture is a balanced mixture of dissolved salts and other soothing chemicals, plus some ingredients that fight certain bacteria likely to invade the eyes.

The tear glands are surrounded and controlled by teams of facial muscles. When the eyelids blink, a small helping of the precious lotion is squeezed by other things, besides the blinking eyelids. When we cry or laugh a lot, facial muscles are pulled out of shape. The tear glands are squeezed, spill out their magic lotion and manufacture more to replace it. The teary lotion slops over and spills down the cheeks.

The blinking operation uses only a tiny droplet of teary moisture. After wiping the surface, the used liquid drains away through a tiny hole at the inside corner of each eye. But a flood of tears flows too fast for the drainage system.

The drainage hole is the tear duct, which empties into a small tube in the back of the nose. During a crying spell, some of the extra liquid floods down the tear duct into the back of the nose, adding an attack of sniffles to an already miserable situation.