"Breathe in. Feel the air pass through your nostrils and move into your nose. Your diaphragm contracts, pulling the air deep into your chest. Oxygen floods into tiny cavities in your lungs and travels into your capillaries, ready to fuel every cell in your body. You're alive. So is that breath you just took. When we inhale, our nostrils capture millions of invisible particles: dust, pollen, sea spray, volcanic ash, plant spores. These specks in turn host a teeming community of bacteria and viruses. Most of the microbes in the air do us little or no harm, and some almost certainly do us good. The truth is, we still understand precious little about them." From: Small Small World, The New Age of Exploration, January 2013 National Geographic, 125th Anniversary Issue