Some colds are like mice, timid and annoying; others like dragons, accompanied by body aches and deep misery. In AH-CHOO , Jennifer Ackerman explains what, exactly, a cold is, how it works, and whether it's really possible to "fight one off." Scientists call this the Golden Age of the Common Cold because Americans suffer up to a billion colds each year, resulting in 40 million days of missed work and school and 100 million doctor visits. They've...