Cover page from published book 'Mecanisme de la Physionomie Humaine', depicting Guillaume-Benjamin Duchenne applying electrodes to a male patients and a headline 'Electro-Physiologie Photographique'. The book was incorporated by Duchenne de Boulogne; photographer Adrien Tournachon and published by Jules Renouard, Paris, in 1862.

Cover page from Duchenne's book, 'Mécanisme de la Physionomie Humaine', published by Jules Renouard, Paris, in 1862.

In 1856, Duchenne began to photograph inmates of the Saltpetriere mental hospital in Paris, where he worked. He devised an experimental method for activating individual muscles in the face by applying electrodes to male and female volunteers. Duchenne believed that each muscle represented a 'movement of the soul' and he listed 53 emotions that could be classified in terms of muscular action. In this photograph we can see Duchenne, on the left, applying electrodes to the face of one of his volunteers.

Duchenne's photographs were taken with the assistance of Adrien Tournachon (1825-1903) who was the younger brother of the celebrated Parisian photographer Gaspard Felix Tournachon (1820-1910), better known as Nadar.