Plates from Guillaume-Benjamin Duchenne's Mécanisme de la physionomie humaine, published by Jules Renouard, Paris, in 1862. By applying electrodes to male and female volunteers, Duchenne was able to activate individual muscles in the face. He saw the human face as a map, the features of which could be codified into universal taxonomies of inner states, with each muscle representing a 'movement of the soul'. He listed 53 emotions that could be classified in terms of muscular action.