Tim Cabeceiras, age 12, of South Prairie, Wash., for his question:

WHAT ARE TEARS?

Tears are mostly a salt solution called lachrymal fluid. It is a substance that fights bacteria and helps make the eye immune to infection. Secreted by two lachrymal glands, one located over each eye and behind the eyelid, the fluid enters through several small ducts in the underside of the lid. Each time a person blinks his eyelids, a little bit of fluid is sucked from the glands. Some emotions, such as grief or anger, can cause the muscles around the lachrymal glands to tighten up and squeeze out additional tears.

After the tears pass across the eyeball, they flow out through two lachrymal ducts that open at the inner corner of each eye. They lead to a lachrymal sac and then on to the nasal duct. Flowing tears while crying can also cause the nose to run because of this connection.