Animal magnetism. Satirical artwork depicting a horse (left) and an animal magnetism practitioner (centre) and pharmacist (right). The theory of animal magnetism was developed by the German physician Franz Mesmer (1734-1815) in the 1770s. It involved manipulating a magnetic fluid thought to reside in living objects. The practice was later renamed 'mesmerism', and eventually led to the development of hypnosis. This copy of a French artwork is from the German book 'Die Karikatur und Satire in der Medizin' (Caricature and Satire in Medicine, 1921) by the German art historian and physician Eugen Hollander (1867-1932).