CNN recently interviewed a young woman doctor who had just returned from working in Africa. The reporter asked her the principal difference between practicing medicine in Mozambique and in the United States. "In Mozambique the people bring me little gifts," she told the interviewer. "A fistful of walnuts, some eggs, a chicken, whatever they can to express their gratitude.

"In the States," she said, "I get sued."

What kind of gratitude is that?

"Gratitude is not only the greatest of virtues, but the parent of all the others," said the Roman philosopher Cicero.

In America, we put gratitude on the calendar -- the fourth Thursday of November each year. You may recall your early American history -- two-thirds of the Pilgrims did not make it to the first Thanksgiving they celebrated. Harsh conditions and little food were daily challenges. According to H.U. Westermayer: "The Pilgrims made seven times more graves than huts. No Americans have been more impoverished than these who, nevertheless, set aside a day of thanksgiving."

But is one day really enough?

Two psychologists, Michael McCollough of Southern Methodist University in Dallas and Robert Emmons of the University of California at Davis, conducted an experiment on gratitude and its impact on well-being. Participants were divided into three different groups and asked to keep diaries. The first group wrote what happened during the day without being told specifically to write about either the good or bad things. The second group was told to record their unpleasant experiences. And the last group was instructed to make a daily list of things for which they were grateful.

The results of the study indicated that daily gratitude exercises resulted in higher reported levels of alertness, enthusiasm, determination, optimism and energy. In addition, the gratitude group also experienced less depression and stress, while helping others more and making greater progress toward achieving personal goals.

This is just one of the studies that gratitude expert Lisa Ryan writes about in her new book, "The Upside of Down Times: Discovering the Power of Gratitude." Ryan says: "Gratitude is not a now-and-then thing. We need a consistent practice of acknowledgement to keep our appreciation muscles strong."

She recommends keeping a gratitude journal, sending thank-you notes and cards, and consistently acknowledging and appreciating the people who make a difference in our lives.

Ryan writes: "Because the mind cannot experience two opposite emotions at the same time, it's important to keep yourself in a state of gratitude as often as you can. For instance, the next time you are having a bad day, take a moment to think about something that you're grateful for and you will start to move into a happier place."

She divides her book into four sections using the acronym SHOW. "S" is for Self because gratitude improves your attitude and outlook. "H" is for Health -- improved physical health results from appreciation. "O" is for Others -- acknowledgement influences and improves our relationships. "W" is for Wealth -- gratefulness has a positive impact on your bottom line.

One of the points that really struck me in her book is how people respond to receiving a "thank you" today. People now say, "It's no problem" ... "It's nothing" ... "Don't worry about it." Ryan says that's the same as taking a gift and throwing it back. We should accept the gift with a simple, "You're welcome."

Even when you can't acknowledge the gift-giver, you should still adopt an attitude of gratitude. Here's a story you might remember by Daniel Defoe.

When Robinson Crusoe was shipwrecked on his lonely isle, he drew up in two columns what he called the evil and the good. He was cast on a desolate island, but still alive -- not drowned, as all his ship's company were. He was divided from mankind and banished from human society, but he was not starving. He had no clothes, but he was in a hot climate where he didn't need them. He was without means of defense, but he saw no wild beasts, such as he had seen on the coast of Africa. He had no soul to speak to, but God had sent the ship so near to the shore that he could get out of it all things necessary for his wants. So he concluded that there was not any condition in the world so miserable that it didn't contain something positive for which to be thankful.

Mackay's Moral: Gratitude should be a continuous attitude.

Harvey Mackay is the author of the New York Times best-seller "Swim With the Sharks Without Being Eaten Alive." He can be reached through his website, www.harveymackay.com, by emailing harvey@mackay.com or by writing him at MackayMitchell Envelope Co., 2100 Elm St. SE, Minneapolis, MN 55414.