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. The book's story opens along the Eastern Mediterranean, where it examines how Pre-Socratic philosophers related the soul to air-wind or pneuma. It then traces what Hippocrates, Plato, and Aristotle wrote about this pneuma, and how Stoic and Epicurean philosophers approached it. It also visits Alexandri ... More

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. The book's story opens along the Eastern Mediterranean, where it examines how Pre-Socratic philosophers related the soul to air-wind or pneuma. It then traces what Hippocrates, Plato, and Aristotle wrote about this pneuma, and how Stoic and Epicurean philosophers approached it. It also visits Alexandria, where Hellenistic anatomists provided new thoughts about the nerves and the ventricles. Thereafter the book shows how Galen's pneuma psychikon or spiritus animae would provide an explanation for sensations and movements. Galen's writings would guide science and medicine for well over a thousand years, albeit with some modifications. One change, found in early Christian writers Nemesius and Augustine, involved assigning perception, cognition, and memory to different spirit-filled ventricles. The book then turns to how questions began to be raised about it in the 1500s and 1600s. Here it examines the rise of modern science. Nevertheless, the animal spirit doctrine continued to survive because no adequate replacement for it was immediately forthcoming. The replacement theory stemmed from experiments on electric fishes started in the 1750s. Additional research eventually led scientists to abandon their time-honored ideas. The book traces some of the developments leading to modern electrophysiology and ends with an epilogue centered on what this history teaches us about paradigmatic changes in the life sciences.