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Invisible organisms called microbes are everywhere: in soil, oceans, and snow; in the food we eat and the air we breathe - even inside our bodies. But in Antony van Leeuwenhoek's time, people believed that what they could see with their own eyes was all that existed in the world. Using microscopes of his own design, Antony discovered a living world no one had seen before. How did the simple tradesman - who didn't go to college or speak English or Latin, like all the other scientists - change everyone's minds? Proving that remarkable discoveries can come from the most unexpected people and places, this eye-opening chapter book, illustrated with lively full-color art, celebrates the power of curiosity, ingenuity, and persistence. --

This book examines the history of Western attempts to explain how messages might be sent from the sense organs to the brain and from the brain to the muscles. It focuses on a construct called animal spirit, which would permeate philosophy and guide physiology and medicine for over two millennia.