While viruses and bacteria are responsible for some of the deadliest diseases known to man, they also play an essential role in maintaining life on earth. This is a fascinating overview of the scientists who discovered various viruses and bacteria, how we have learned to fight the harmful ones and use the beneficial ones to improve our lives. "National Geographic Investigates" introduces young people to cutting edge techniques of scientific investigation, the most current discoveries, and the way that those discoveries are interpreted to throw new light on our understanding of ourselves and the world around us.Special features include: map showing major sites discussed in the book, plus locator maps to start each chapter; sidebars explaining the latest technology being used by scientists; a 'Meet the Expert' sidebar presenting an interview with a scientist currently working on the appropriate field; timelines placing research and researchers in historical context and pinpointing the time period for each chapter; and, lavish design including photographs, illustrations, and diagrams.