In 1665, an infectious disease swept through the British capital and claimed the lives of tens of thousands of people. It would take another two hundred years for the cause of the Great Plague of London to be confirmed: a powerful bacterium called Yersinia pestis. In those centuries, our understanding of diseases was transformed. In So Very Small, Thomas Levenson reveals how human hubris led us to overestimate our own ability and underestimate the threat that microorganisms truly pose. He journeys through some of the most significant epidemics and pandemics in history, including the recurrent outbreaks of cholera in Europe and Asia, and the 1721 Boston smallpox epidemic. The turning point came in the nineteenth century with the development of germ theory: the concept that microbes can cause disease. Levenson shows how, in the years that followed, scientists made major breakthroughs in our ongoing struggle against infectious disease. Perhaps the greatest of these achievements is the