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...