In 1979, Norman Cousins, then editor of the Saturday Review, published his book Anatomy of an Illness as Perceived by the Patient, which remained on the New York Times best-seller list for more than 40 weeks. The book describes the author's miraculous recovery from a normally incurable disease.

How did Cousins recover? He laughed. After taking himself off all prescriptions except intravenous vitamin C, he laughed his way back to health by watching episodes of Candid Camera provided by his friend Allen Funt, viewing old Marx Brothers films and having his nurse read to him from books of humor during the late night hours.

Laughter, as Cousins discovered, brings numerous positive physical effects to the human body. Here are just a few:

• Muscle relaxation. When you are laughing, the muscles that are not participating in the laughter immediately relax. As soon as you finish laughing, the muscles that were participating in the laughter relax, too.
  
• Activation of the immune system and reduction of stress. In a 1996 study researchers proved that after laughing a great deal, participants' immune systems kicked into overdrive for at least 24 hours. In addition, there was a drastic reduction of at least four stress-causing hormones in their bodies.
  
• Pain reduction. In one study published by the Journal of Holistic Nursing, patients were told one-liners before painful medication was administered and after surgery. The results suggested that those who were exposed to humor perceived less pain when compared with patients who did not receive a "dose" of humor as part of their therapy.
  
• Cardiorespiratory exercise. Some physicians refer to laughter as "internal jogging" because it causes your heart rate to increase as it does when you exercise. Laughter also gives other parts of your body a good workout. It is great for your diaphragm as well as your abdominal, respiratory, facial, leg and back muscles. It massages organs, tones intestinal functioning and strengthens the muscles that hold the abdominal organs in place.