This monograph is dedicated to the lives and scientific achievements of the physiology pioneers Warren and Margaret Lewis. Their story spans the first half of the 20th century, from their respective educations through early, independent research to joint research from 1910 to 1955. Among the numerous developments they initiated, were the discovery of pinocytosis, the beginnings of video microscopy and the development of the first mammalian tissue cultures. Their research expanded the theoretical knowledge of cell structure and function. On a more practical level, they advanced many laboratory methods, like the first recipes for culture media. The text is beautifully enriched with personal anecdotes about their lives. This is the story of two scientific pioneers in the context of early 20th century biology and physiology. It is an inspiration for senior and aspiring researchers.