BY Judy Overton

In a typical day, each of us swallows 30 milliliters of mucus from our lungs. A mucus blanket is swept from the most distant airways up the trachea and swallowed all day long.

At the same time, we breathe 10,000 liters of air that is full of microorganisms -- bacteria, fungi, and viruses. The microorganisms deposited in our lungs land on the mucus and stick to it. Normally the mucus is moved out of the lungs by efficient action...