'Photographic Electro-Physiology', an illustration from Duchenne de Boulogne's (1806-1875) book, 'Mecanisme de la Physionomie Humaine', published in 1862. Duchenne (left), applies electrodes to the face of one of his volunteers. In 1856, Duchenne began to photograph inmates of the Salpetriere mental hospital in Paris, where he worked. He devised an experimental method for activating individual facial muscles in the face by applying electrodes to volunteers. He believed that each muscle represented a 'movement of the soul' and he listed 53 emotions that could be classified in terms of muscular action. He was assisted by Adrien Tournachon (1825-1903), younger brother of the celebrated Parisian photographer Gaspard Felix Tournachon, better known as Nadar.
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