Mesmerism

Franz Anton Mesmer proposed that a single subtle fluid, animal magnetism, pervades the universe and every living body, flowing through the body along invisible channels much as blood flows through vessels; illness, in his account, resulted when this flow became blocked or unevenly distributed, and health could be restored by a trained magnetizer who used touch, gesture, eye contact, and sustained concentration to redirect and rebalance the patient's magnetic fluid. Mesmer's Paris practice from 1778 became famous for its theatrical group sessions: patients sat around a large wooden tub, the baquet, filled with iron filings and water, holding iron rods that projected from it, in a dimly lit room with mirrors and soft music, while Mesmer or his assistants moved among them making magnetic passes. Many patients experienced dramatic responses, trembling, weeping, convulsions, or fainting, that Mesmer called a healing crisis, after which some reported real relief from their symptoms.

Mesmer's system spread quickly among Paris's fashionable and intellectual circles in the early 1780s, and he trained a number of students and associates, including Charles Deslon, a royal physician who became his most prominent practicing follower and who was the specific practitioner tested when the French crown eventually intervened. The theory's dramatic public success and its association with fashionable, sometimes overtly erotic, mixed-gender group treatment also drew serious concern from the medical establishment and eventually from the French crown itself, setting up one of the more consequential scientific investigations of the eighteenth century.

In 1784, alarmed by animal magnetism's popularity, Louis XVI convened a royal commission of physicians and scientists, including Benjamin Franklin, then American ambassador to France, chemist Antoine Lavoisier, and astronomer Jean-Sylvain Bailly as its head. Rather than simply observing Mesmer's associate Charles Deslon at work, the commissioners designed genuine tests: they blindfolded subjects and told some they were being magnetized when they were not, and magnetized others without telling them, comparing whether the crisis reactions tracked the subject's belief or the actual presence of the claimed fluid. Presented to the king on 11 August 1784, the commission's report concluded that no physical magnetic fluid could be detected and that the treatment's real effects came entirely from imagination and suggestion; historians of medicine now regard the design, its use of blinding and sham alongside genuine procedures, as one of the earliest examples of a controlled clinical trial.

The 1784 report effectively ended Mesmer's own career in France, though animal magnetism as a claimed physical force never entirely disappeared from fringe practice in the decades after. Its more lasting legacy runs through the trance states mesmerists had genuinely, if unknowingly, learned to induce. Scottish surgeon James Braid, after witnessing a mesmeric demonstration in the 1840s, showed that the same trance could be produced through simple visual fixation and suggestion, with no magnetic fluid required, and in his 1843 book Neurypnology he coined the term hypnotism. That reframing let the phenomenon survive the collapse of the theory that first produced it, becoming the basis for hypnosis as a legitimate subject of ongoing study, separate from animal magnetism's discredited physics.