Johannes Muller (1801—1858) was by many accounts the most innovative and important physiologist of the nineteenth century in Germany. Until he arrived on the scene, intellectuals at universities across the country were inclined to engage in unfounded speculation over natural-physiological issues. Johannes Muller elevated German biological research to a higher level by launching a new era in scientific knowledge would be based on systematic observation and physiological experimentation. Muller challenged his fellow scientists to abandon their proclivity to speculate and instead to approach their work with more serious and balanced contemplation, perseverance, and an unwavering commitment to the truth.
Johannes Muller also made various original and essential discoveries to the fields of physiology, anatomy, embryology, histology, and zoology. His contributions to the field of neurophysiology were especially important, including his work that conclusively established the distinctions between motor and sensory nerves. Together with his other contributions to neuroscience, this work overturned the old view of nerves as passive, interchangeable conductors by showing that each type of nerve was associated with its own specific nervous energies and qualities—that visual nerves, for example, will convert stimuli of any type into a visual experience. Appreciative German physiologists who achieved recognition after Muller almost universally acknowledged their indebtedness to him and to his perspectives and methods. His distinguished pupils included Carl Ludwig, Rudolf Virchow, Hermann von Helmholtz, and Max Schultze. Untold others were deeply influenced by his paradigm-shifting Handbuch der Physiologie des Menschen.