For much of the nineteenth century the popular idea of science in general was based upon the notion of "vitalism," the belief that no living phenomenon could be defined or described by purely physical and chemical principles. Some unknown force, distinct from any other natural force, conditioned every action, whether it was magnetic, electric, or some other phenomenon of unseen waves.

Scientists at the time were fascinated by invisible fluids and forces in everything from miraculous gases to Isaac Newton's gravity and Benjamin Franklin's electricity. It was Franz Anton Mesmer (1734–1815) who named this force "animal magnetism" and described it as an extremely subtle universal fluid that permeated all things, ebbing and flowing in a kind of magnetic tidal manner. Whoever could control this fluid as it entered the human body could control illness and heal various diseases.

Mesmer's invisible fluid incorporated both religious...