Mesmerism is an 18th-century healing practice based on the belief that an invisible magnetic fluid flows through all living things and that illness results from blockages in this fluid’s circulation. Developed by the German physician Franz Anton Mesmer, the practice involved hand gestures, iron rods, and trance-like states meant to restore the body’s natural flow. Though thoroughly debunked by the 1780s, mesmerism left a lasting mark on medicine: it gave rise to modern hypnosis and, perhaps more importantly, inspired the first placebo-controlled experiments in history.
Mesmer’s Theory of Animal Magnetism
Franz Anton Mesmer believed a universal fluid permeated the natural world, connecting human bodies to the planets and to each other. He called this force “animal magnetism,” distinguishing it from the magnetism of minerals or metals. In his view, disease occurred when this fluid was unevenly distributed or blocked within the body, and a skilled practitioner could redirect it to restore health.
Mesmer laid out these ideas formally in 1779, publishing twenty-seven propositions in his treatise on the discovery of animal magnetism. He first tried to win over the medical establishment in Vienna, where he practiced, but met resistance. He then moved to Paris, where his dramatic group healing sessions made him a celebrity and a lightning rod for controversy.
What a Mesmerism Session Looked Like
Early on, Mesmer had patients swallow iron filings and then waved magnets around their bodies. He later abandoned both the magnets and the iron filings after discovering that simply using his hands produced the same effects. These hand movements, known as “passes,” became the signature technique of mesmerism. The practitioner would sweep his hands slowly over the patient’s body without touching it, supposedly directing the magnetic fluid where it needed to go.
Group sessions were more elaborate. Patients, mostly women, sat around a large wooden tub called a baquet, filled with “magnetized” water, powdered glass, and iron filings. Bent iron rods protruded from the tub’s lid, and patients pressed their afflicted body parts against them. A rope coiled loosely around the group, and participants held hands to create a circuit, much like an electrical loop. Mesmer would move through the room making passes with his hands, sometimes touching patients with a wand, while music played in the background.
The goal of each session was to provoke what Mesmer called a “crisis.” Patients would enter a trance-like state, then begin to shake, convulse, writhe, or faint. Contemporaries compared these episodes to the jolt from a Leyden jar, the recently invented electrical capacitor that sent a violent shock through anyone who touched it. Mesmer considered the crisis essential to healing: the convulsions supposedly marked the moment the body’s magnetic fluid was being unblocked and rebalanced.
The Franklin Commission’s Verdict
By the early 1780s, mesmerism was popular enough in Paris to alarm the French medical establishment. In 1784, King Louis XVI appointed a royal commission to investigate. The panel included some of the most prominent scientists alive: Benjamin Franklin, the chemist Antoine Lavoisier, and the astronomer Jean Sylvain Bailly, among others.
The commissioners chose a specific question to test. Rather than asking whether patients felt better after treatment, they asked whether the magnetic fluid existed at all. Their reasoning was straightforward: if the fluid didn’t exist, any reported cures couldn’t be caused by it.
To find out, they designed what became the first placebo-controlled experiments in medical history. They gave patients objects that had supposedly been “mesmerized” but actually hadn’t, and secretly administered genuinely treated items without telling patients. If a patient reacted to a fake treatment or failed to react to the real one, the claim fell apart. That is exactly what happened. Patients responded based on whether they believed they were being treated, not on whether they actually were. The commission concluded that animal magnetism “has no existence” and that its effects must be attributed to “the imagination.”
What makes this investigation remarkable is how casually the commissioners introduced placebo controls. Franklin and Lavoisier were well-read in Renaissance theories of medical skepticism, particularly the writings of Montaigne, and they adapted an existing methodology for settling competing claims. But applying it to a medical question this rigorously was new, and their approach became a template for modern clinical trials.
From Mesmerism to Hypnosis
The Franklin Commission discredited Mesmer’s theory, but it didn’t kill the practice. Mesmerism continued to attract followers across Europe for decades. What eventually replaced it was not another debunking but a reinterpretation. In the 1840s, the Scottish surgeon James Braid watched a mesmeric demonstration and concluded that the trance state was real, even if the magnetic fluid was not. He proposed that the effects came from concentrated attention and nervous fatigue rather than invisible forces. Braid coined the term “hypnotism” to describe this phenomenon, deliberately replacing the word mesmerism to distance the trance state from Mesmer’s discredited theory.
This shift mattered because it moved the explanation from the practitioner’s supposed power to the patient’s own mental processes. Mesmer believed he was channeling a physical force into people. Braid argued the patient’s mind was doing the work. That reframing opened the door for serious psychological research into suggestion, trance, and focused attention.
Mesmerism’s Lasting Impact on Medicine
Mesmerism is often remembered as quackery, and the underlying theory certainly was. But the investigation it provoked had consequences that outlasted Mesmer himself. The Franklin Commission’s experiments helped establish the concept that a patient’s belief in a treatment can produce real physical effects, an insight now central to our understanding of placebo responses. The commission’s report has been interpreted as negative about the literal theory of animal magnetism but actually supportive of the therapeutic power of suggestion and positive thinking.
This connection runs deeper than historical curiosity. The methods Franklin and Lavoisier developed for testing mesmerism, comparing real treatments against shams while keeping patients unaware, became the foundation of placebo-controlled trials. The nefarious reputation that placebo effects carry in medicine today (something to control for, something that fools patients) traces partly back to these experiments and the language the commission used to describe imagination as a source of false cures.
Mesmerism also fed directly into modern psychotherapy. The observation that trance states and suggestion could alter how people experienced pain and illness became a forerunner of cognitive therapies used today for depression, chronic pain, and anxiety. Hypnosis, mesmerism’s direct descendant, is now a recognized clinical tool with applications in pain management, habit change, and psychological treatment. The magnetic fluid was fiction, but the human capacity for suggestion that Mesmer stumbled onto was very real.