The author writes of this book: "'What lead you to impersonate great biologists?' is a question often asked of me. My answer varies depending upon the interviewer. Sometimes I cite my interest in biographies of distinguished scientists initiated by a reading of Vallery-Radot's The Life of Pasteur as a teenage and furthered by a superb college course on the history of biology. Another answer: my love of the theater, more from the balcony than on the stage as a ham actor. My most frequent reply, however, credits this instructional innovation to the students in my Berkeley course in general biology (Zoology 10), who began to show, in the late sixties, their dissatisfaction with the lecture system. "I gave serious thought to the problem of communicating biological information with greater impact. One morning in the shower I was stuck not only by the spray but also by an idea: dress up and make up as some of the great biologists and present their discoveries and thoughts in their own words. In addition to expounding their scientific work, portray them as persons with hopes and ambitions, frustration over failure, and joy from success. I chose Darwin, Mendel, Harvey, and Pasteur, who would probably be on the most lists of great biologists, and two lesser-known scientists: William Beaumont, pre-Civil War Army surgeon who studied gastic digestion in the stomach of a fur-trapper, Alexis St. Martin; and Hans Spemann, 1935 Nobel Laureate in Physiology and Medicine, who discovered the organizer principle in embryonic development. The results of the innovation, which I call guest lecturers, were gratifying. "Late five of the lectures, in abbreviated form, were recorded on motion picture film (available through the Media Center of the University of California, Berkeley). Then it was suggested that a much wider audience should be reached through publication of the lectures in book form, illustrated with photographs of the 'guest lecturers' in action and with drawings, charts, maps, and reproductions of lantern slides." This title is part of UC Press's Voices Revived program, which commemorates University of California Press's mission to seek out and cultivate the brightest minds and give them voice, reach, and impact. Drawing on a backlist dating to 1893, Voices Revived makes high-quality, peer-reviewed scholarship accessible once again using print-on-demand technology. This title was originally published in 1975.