Theodor Wilhelm Engelmann (1843-1909), German physiologist and botanist. Engelmann's main area of research was the physiology of nerves and muscles, but he also conducted important experiments with bacteria and algae. He was the first to show that the stimulus for the contractions of the heart came from the cardiac muscle itself and not a nerve. He proposed that striated muscle contractions were the result of interactions between bands of muscle fibres. Engelmann was the first to demonstrate that bacteria move toward sources of oxygen (aerotaxis), and in doing so also showed that photosynthesis took place within the chloroplasts of a plant or alga.