In an absorbing monograph entitled Mécanisme de la physionomie humaine, Duchenne de Boulogne proposed that each emotion has its own specific facial muscle. Employing the most recent and exciting technical inventions of the mid nineteenth century, Duchenne used faradism to stimulate the facial muscles and photography to record their actions. Using electrical stimulation, he virtually dissected by this novel method the sheets of facial musculature into a number of emotional entities. By masking the stimulated area, he proved that no reflex activity occurs elsewhere in the face—an illusion hitherto accepted almost universally. Classical sculpture which purported to show a specific emotion was resculpted by Duchenne de Boulogne to show the proper use of the specific facial muscles for that emotion. The concept of emotional expression as a basis for muscle classification in the face is shown to be stimulatingly original, although not entirely valid as a scientific basis for physiological research.
But the great individualist Duchenne ventured into yet another area. The first use of photography to illustrate clinical cases was in the middle of the nineteenth century. In 1862 Duchenne de Boulogne published two albums of photographs with accompanying text which appear to have been the first publicly published volumes using photographs of clinical material. The Album de photographies pathologiques contained photographs of clinical entities later linked eponymously with Duchenne, while the Mécanisme de la physionomie humaine presented scores of original prints, some including Duchenne himself in photograph.