Water plant operator Torrey Jones checks the clarity of a sample of treated water at the Beaver Falls Municipal Authority water treatment plant in Beaver Falls, Pa. Keith Srakocic/AP hide caption

itoggle caption Keith Srakocic/AP

University of Miami pediatrician Judith L. Schaechter gives an HPV vaccination to a 13-year-old girl last week in Miami. Joe Raedle/Getty Images hide caption

itoggle caption Joe Raedle/Getty Images

Seeds from Golden Rain acacias like these in Wales provide the active ingredient for a pill to help people stop smoking. Tom Patterson/Flickr hide caption

itoggle caption Tom Patterson/Flickr