Duchenne's physiognomy studies. Man with a facial expression induced by electrical probes applied by French neurologist Guillaume Duchenne (1806-1875). Duchenne used the new technique of photography to record idealised facial expressions that he claimed revealed the emotions of the soul. Stimulated here are the zygomaticus major and corrugator supercilii muscles. Photograph from the 1876 edition of Duchenne's 'Mecanisme de la physionomie humaine' (The Mechanism of Human Physiognomy, 1862). This work was subtitled: 'The Electro-Physiological Analysis of the Expression of the Passions, Applicable to the Practice of the Plastic Arts'.