Pat O'Grady, age 13, of Ottawa, Ontario, Canada, for his question:

Why are tears salty?

All of us, young and old, have a right to shed a few tears now and then. When they spill down the cheeks, we notice that the sorrowful liquid has a salty taste. Most other body fluids also are slightly seasoned with sail. However, they contain a multitude of other chemicals and when analyzed the total body fluids somewhat resemble diluted solutions of ordinary seawater. This curious fact tempted scientists to probe into the remote biological past. Their research may or may not have some bearing on why our tears are salty.

The human body is made from about 30 ordinary chemical elements and 65 per cent to 70 per cent of its total weight is water. However, its basic elements are in the form of several delicately blended chemical solutions. The tissue cells are bathed in liquid lymph, the blood cells circulate in liquid plasma. Two spongy glands create a very special chemical formula to bathe and soothe the eyes, plus an emergency supply for tears.

The blood plasma usually carries more protein type chemicals and the lymph carries more fats. The kidneys, the tear glands and other special organs maintain their own special liquid formulas. However, some researchers suspect that the body fluids may be very much like the water that filled the fresher oceans when the earth was young.

Everyday, the rains and runoffs dissolve soluble chemicals from the land and dump them into the sea. Though the sun evaporates its water vapor, its dissolved chemicals are left behind. This has been going on for more than four billion years and the chemical broth in the ocean gets stronger every year. Nowadays, a dash of seawater makes the eyes sting and is far too strong a solution for washing and soothing them.

But perhaps the milder seas of the remote past were gust right for tears and other body fluids. There is a theory that all life began in those early seas and perhaps our body fluids were designed to match their mild chemical solutions. We cannot prove this theory, but there is a mountain of biological evidence to support it.

In any case, it suggests a possible explanation of why our tears taste salty and perhaps why the other body fluids resemble diluted seawater. Actually, the teary lacrimal fluid is far more complex than salty water. It is a precisely balanced blend of many highly complex chemicals    though the salt content happens to provoke the strongest reaction in the taste buds.

The main purpose of the lacrimal fluid is to wash, and soothe the eyes. It also contains antibiotic ingredients to counteract infections and to heal minor wounds. What's more, as in all body fluids, the lacrimal fluid maintains a delicate balance between its salty and acid ingredients. The salty ingredients just happen to taste the strongest.