The Franklin Commission on Animal Magnetism

The commissioners grasped the crucial distinction at once: patients were plainly having experiences, and the question was not whether but why. Mesmer's associate Charles Deslon cooperated, which is why the tests could be run at all. In the best known of them, Deslon magnetised one tree in the garden at Passy, and a young man reported to be highly susceptible was blindfolded and led to embrace several trees in turn; he convulsed at the fourth, which had not been touched. In another, a woman was seated before a closed door and told that Deslon was magnetising her from the far side.

Nobody was there. She responded. The order was then reversed: Deslon magnetised her while she believed nothing was happening, and she did not respond. A series of variations on this pattern all produced the same asymmetry, effects following the subject's belief and never the treatment. The reasoning is worth stating plainly, because it is the whole of what modern trial design does. If a claimed agent produces its effect only when the subject knows it is present, the subject's knowledge is doing the work and the agent is not. Mesmer himself refused to take part, holding that Deslon's practice was a degraded version of his own, so the commission tested the method as Deslon administered it rather than as its originator would have wished.

Two bodies reported in 1784. The one chaired by Benjamin Franklin drew on the Academy of Sciences and the Faculty of Medicine and included Antoine Lavoisier and Joseph-Ignace Guillotin, with the astronomer Jean-Sylvain Bailly writing the report. A second, from the Royal Society of Medicine, worked separately and reached a similar verdict, with one member declining to sign: the botanist Antoine Laurent de Jussieu argued that the commissioners had disproved the fluid without accounting for the effects, and that something in the interaction between operator and patient still required explanation. He was right about the gap, and it took sixty years for anyone to take it up properly.

The commissions had established that imagination could produce convulsions, insensibility and relief, and then filed that under refutation rather than under discovery. James Braid picked the observation back up in the 1840s, renamed the state hypnotism, and located it in the subject rather than the operator, which is the line that runs into modern clinical practice. The 1784 reports are therefore both the founding document of controlled testing and a case study in how a negative finding can discard a positive one.