Many people still have the teddy bear or doll they had when they were chilldren. But Harriet Lasky of Denver,Colorado, has kept a different souvenir, a piece of chewing gum. She has kept it for thirty-three years,since she was seven. She chews it during the day and keeps it in a glass of water at night. ' It gets better with age,' she commented while she was chewing the gum.