"Tears, idle tears, I know not what they mean." Alfred Lord Tennyson

It happens at the best of times and the worst of times. At births and deaths, in pain and pleasure, over defeat and victory -- we cry.

Although poets have pondered the nature of tears since Ovid noted "it is relief to weep" back in 43 B.C., "no one really knows why we shed emotional tears," says biochemist William H. Frey II.

Scientists know the physiological reasons for continuous tears -- the ones that keep our eyes moist, he says, and irritant tears -- like those secreted when chopping onions. But emotional tears, claims Frey, remain a mystery.

One of the first scientists to explore emotional tears -- which are unique to human beings -- was Charles Darwin. His conclusion that they are "an incidental and purposeless part of the crying process," says Frey "has been accepted by many scientists since then."

But the 32-year-old researcher considers it "very unlikely that evolution favored a purposeless process," and has developed his own intriguing theory: that tears are nature's way of excreting bodily chemicals that build up in response to stress.

Frey's hypothesis is based on two observations -- that people claim to feel better after crying and that other exocrine functions (sweating, exhaling, urinating) involve removal of toxic materials.

"From a biochemical viewpoint," he says, "people who are sad or depressed could be suffering from a chemical imbalance . . . that is restored, at least partially, by the excretion of certain substances in tears.

"I submit that the excretion of tears is central, not incidental, to the relief mechanism. So when people say they want to 'cry something out' this may be literally what occurs."

Frey is currently testing his theory at Minnesota's St. Paul-Ramsey Medical Center by collecting and analyzing the chemical content of irritant tears and emotional tears.

"If it turns out that they do (differ chemically)," he says, "we will have taken the first step in determining whether the theory is correct."

So far he has collected tears from more than 100 people who responded to newspaper ads asking "Will You Cry for Us?" For anywhere from $3 to $10 per session the respondents sat through a tear-jerker movie ("Brian's Song" proved one of the weepiest) then returned to cry over chopped onions.

He also plans to gather tears shed while laughing, but so far has collected only enough "hilarity tears" from one person. "Getting people to weep emotionally . . . and collecting the tears in a small test tube is hard enough," he notes. "How do you get someone to laugh so hard they cry? Tell jokes?"

Early results have been gratifying. "We did find a substantially significant difference in the amounts of protein," says Frey, adding that it's too soon to draw a definitive conclusion.

But if his theory proves true, "people who condition themselves out of the natural crying process may do themselves harm. For example, it's known that the incidence of peptic ulcer, which is a stress-related disease, is higher in males than in females. And females don't have as great a social stigma against crying as males.

"Our crying behavior, then, may be important in determining our susceptibility to stress-related diseases," adds Frey, who says he sheds emotional tears "maybe once every three or four months." Some people report crying 25 times a month and others say they haven't cried since they were 12."

Crying can reduce stress, confirms stress guru Dr. Hans Selye. "Crying is sort of an external realization of internal emotion, a cutting loose," says the head of the International Institute of Stress. "If someone terribly wants to cry, surpressing it may call forth a stress reaction."

Although "the circumstances under which most people with stress cry is grief," says psychotherapist Lynn Brallier, director of the Stress Center of Washington, "the body and mind work together to release energy in crying over a variety of emotions."

"Some people -- most often women -- explode in tears during orgasm. Some people cry in fits of rage or frustration -- when they don't get what they want -- as sort of an unconscious tantrum."

Although some contend that all tears are sad tears ("joyous" weeping at a wedding, for example, really being "sad" tears over lost childhood) Brallier disagrees.

"I feel there are definitely tears of bliss," says Brallier, adding that there can be stress even in happy situations -- like accepting an award -- that may need tearful release.

"Many people cry during a religious or mystical experience or when they are terribley moved by the beauty of nature or art. They may be expressing a sense of fulfillment, of mystical connection with some powerful force."

Not only can "a good cry" be pleasurable, she says, "it't the best way to clear up a trauma in life." In her work with cancer patients and their families "no one wants to cry in front of the others and upset them.

"So my job is to get them all together and cry at once. After a very upsetting, tearful session everyone feels such relief, and communications are open again."

Since Brallier feels "crying is healing to the body" she is "kind of tough with people about how they cry. Welling up tears in the eyes or whining a little whine isn't enough. You've got to really let it go."

Although she doesn't condone the advice of groups like SAGE in San Francisco that advocate daily tears, Brallier says "let yourself cry as immediately as possible when you become aware of the need to cry."

"I wouldn't want to be so California as to cry anywhere, anyplace, anytime. But if you're teaching class or campaigning, don't forget to get back to crying as soon as you can."

To try her tearjerker technique:

1. Ideally, be alone or with someone close. Recreate the scene and how you felt when you wanted to cry.

2. A good cry consists of tears, stuffed-up sinuses, any sound that comes through and deep abdominal breathing.

3. Afterward you should feel pleasantly exhausted. Relax or sleep to continue the healing process.