Mucus' role long misunderstood.

• Position: Respiration

With each breath, we inhale life-sustaining oxygen-rich air, but that same air is riddled with germs threatening our health. "The air we breathe isn't exactly clean, and we take in many dangerous elements every minute," points out Michael Rubinstein, professor of chemistry at the University of North Carolina, Chapel Hill.

"We need a mechanism to remove all the junk we breathe in, and the way that is done is with a very sticky substance called mucus, which lines the airways and catches these particles before they reach the epithelial cells in the lungs. Hair-like extensions of epithelial cells called cilia then propel the mucus out of our airways and get rid of these dangerous particles."

If mucus is so sticky, though, why doesn't it stick to the cilia that get rid of it? Until now, researchers believed that the answer was water, which bathed the cilia and shielded them from the mucus. However, researchers from the Cystic Fibrosis Research and Treatment Center have shown that the water model fundamentally is wrong. Instead, a mesh of molecules resembling a brush is tethered to each hair-like cilium and, as each cilium sways back and forth, the brush collectively propels the...