The research and discoveries made by French chemist and microbiologist in the 1800s have benefitted mankind well into the 21st century. He proved microorganisms cause diseases and developed vaccines. American scientist Henrietta Swan Leavitt contributed to the science of astronomy, specifically regarding the brightness of stars. Inside this guide, readers will explore the lives and discoveries of these historical figures as well as many other notable scientists, The text is supported by stunning photographs and images.