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J R Soc Med. 2005 December; 98(12): 572–575.
PMCID: PMC1299353

Mesmer's 1780 proposal for a controlled trial to test his method of treatment using ‘animal magnetism’

Having been effectively thrown out of Vienna where his supposed cures by ‘animal magnetism’ had aroused both the enthusiasm of some patients and the enmity of most of the medical establishment, Mesmer went to Switzerland and then to France in 1778 where his reputation had preceded him.

In Paris crowds came to see him—some to be treated and some from curiosity.

Mesmer wanted both approbation of his ‘discovery’ of animal magnetism and profit from its exercise and he seems to have believed that the best way to do this was to try to persuade the learned societies of Paris to approve his theory and methods. After a number of unsuccessful approaches to the Académie des Sciences and the Société Royale de Médecine, Mesmer paused in his attempt to persuade the learned1 of the virtues of his theory and concentrated, with great success, on building up a practice treating patients.2

However, Mesmer really wanted the government's approval and hence benefit and profit to him; without this he was adamant that he would not divulge his secrets.

Some time passed before he approached the Faculté de Médecine but, in the meantime, he had made the acquaintance of one of its Regent Doctors, d'Eslon or Deslon.3 Deslon became persuaded of the great utility of Mesmer's method; he said that he did not yet know the nature of the agent involved though he knew the procedure for treatment. He published his observations, just relating the effects he had seen, in 1780.4 Mesmer and Deslon became friends and the latter agreed, as a professor in the Faculté de Médecine, to propose to the Faculté that they examine the discovery.

The Faculté was far from happy, since its members had decided they wanted nothing to do with Mesmer, but they could not refuse the request by one of their own. However, they retaliated by agreeing to a M. de Vauzèmes bringing a charge against Deslon of having damaged the reputation of the Faculté by his espousal of the views of Mesmer, to be heard on the same day that Deslon was to present Mesmer's proposals. The meeting took place on 18 September 1780. The short description given here of events on that day is taken from Mesmer's own account which is unlikely to be unprejudiced. I have included only material that Mesmer quotes verbatim (and which was apparently deposited in writing at the meeting) and have ignored his numerous glosses on it.

De Vauzèmes spoke first and launched a vituperative attack against both Mesmer and Deslon; reading this now one is struck not only by its virulence but by the complete absence of any consideration of whether it might be possible to test Mesmer's claims independently rather than relying on the unfavourable reactions of other learned bodies. He proposed that Mesmer's methods should be rejected out of hand without dignifying them by examination since Mesmer was a charlatan—and a charlatan who had not acted in good faith in his dealings with the learned societies of Paris and whose conduct would be no better towards the Faculté. He was particularly vehement in his assertions that Deslon had demeaned the profession of medicine and damaged the Faculté by associating with, and supporting, Mesmer and by his approval of Mesmer's claims in his recently-published book.5 De Vauzèmes went further and proposed that the Faculté should reject out of hand all such claims for new cures which were contrary to the practice of sound medicine. Deslon then spoke; though he severely criticized the behaviour of the recently founded Société Royale de Médecine towards Mesmer, and flattered the Faculté by insisting that they, on the contrary, were interested only in finding the truth, his discourse was reasoned and the proposals he presented on Mesmer's behalf for a trial of animal magnetism were not unreasonable. The trial was to be confined to observations on whether Mesmer's patients improved more or less than did those treated conventionally.

He proposed a trial in which 24 patients were to be divided into two groups of 12, one group to be treated by ‘ordinary methods’ and the other to be treated by Mesmer.6 To avoid any later arguments about ‘age, temperament, disease or symptoms’, the patients were to be assigned to the groups by drawing lots and the details of duration of treatment and of the examination of the patients were to be decided in advance. A report of each patient's state was to be drawn up and signed by the Faculté's Commissioners, by Mesmer, and by representatives to be appointed by the government; the latter were to be persons not involved in medical practice to avoid any public suspicion of partisanship. All in all it seems a very fair proposition if one accepts that only the change in the patient's state was to be examined and Mesmer's method was to remain secret.

However, the Faculté was determined not to have any truck with Mesmer or his practice. It not only rejected the proposals Deslon had presented on Mesmer's behalf, it also admonished Deslon to behave more circumspectly and threatened that, unless during the next year he repudiated Mesmer's teachings, his name would be deleted from membership of the Faculté at the end of the year. In the meantime Deslon was forbidden to take part in deliberations at meetings of the Faculté.

Mesmer responded to the rejection of his proposals by publishing them in the Journal de Paris, and, in the following year (1781) he published his account of his doings in Vienna and Paris as the Précis historique... (Figure 1). A good deal of feeling was aroused in some quarters that the Faculté had acted very arrogantly in dismissing Mesmer and his methods without any examination of these. It must be remembered, however, that Mesmer steadfastly refused to allow his methods to be scrutinized at all and insisted that only the effects of his treatment should be examined.

Figure 1
Title-page of Mesmer's Précis historique... which contains the text of his proposals for a trial of his treatment by Animal Magnetism presented to the Faculté de Médecine de Paris on 18 September, 1780

For an account of what followed the rejection, of Mesmer's direct appeals to the French government and to the queen, Marie Antoinette, to the setting up of two commissions of enquiry in 1784, and the total rejection of Mesmer's theory by the one commission and of the results of his treatments by the other, see my article in the James Lind Library on the Report of the Royal Commission set up to examine animal magnetism.

Mesmer's proposals that the Faculté rejected on 18 September 1780 largely speak for themselves; they are in many ways remarkably modern in the conditions they set out. The proposal that each patient for the trial should be randomly allocated ‘by the method of lots’ to one of the two groups, to take account of differences between them and their illnesses and to avoid later argument about the outcome, may well be the second earliest instance of random allocation being proposed for a clinical trial. The first such suggestion was, as far as is known in 2005, that by Van Helmont devised about 1643 and published post-humously in the Ortus Medicinae of 1648.7 However, neither Van Helmont's trial nor Mesmer's actually took place.

It may strike the modern reader as extremely odd that anyone could contemplate a trial in which patients with virtually any disease were to be mixed up;8 random allocation—whatever Mesmer said—could not, to our minds, possibly control for having different mixtures of diseases or different numbers of patients with the same disease in the two groups. I think the key to this apparent contradiction between taking care to make the groups comparable by random allocation at the same time as explicitly allowing the groups to contain different mixtures of patients with any disease whatsoever (except venereal diseases), is to be found in Mesmer's theory of disease. He explicitly believed (at least as reported by Deslon9) that there was only one disease and only one cure for it; in fact that animal magnetism was a universal panacea.10 All disease was caused, according to Mesmer, by disturbance of the flow within the body of a universal and all-pervading fluid and all was to be cured by correcting the flow of this fluid using his method of treatment by animal magnetism. There is a sense in which Galenic medicine also took the view that disease was unitary in nature and was always caused by disturbance of the balance of the humours, so it may be that there would have been no qualms on either side when Mesmer and the Faculté jointly chose the 24 patients for the trial, about including any mixture of patients—provided each patient was randomly allocated to a group. Since the Faculté rejected Mesmer's proposals out of hand further speculation on this is idle.

Ironically, in Van Helmont's proposed trial of the treatment of fevers with and without blood-letting, it was Van Helmont who believed that diseases were distinct and had distinct causes and his opponents, the ‘Galenists’, who believed that disease was essentially unitary in its causation. Mesmer, as we have seen, took the ‘unitary’ view. However, Van Helmont also believed in a universal remedy (the Alkahest), though a very different one from Mesmer. There is also room for serious doubt about whether Van Helmont's proposals were ever intended to result in a real trial or whether they were—as I argue elsewhere11—just a rhetorical device to support his arguments against the ‘Galenists’.

Had the Faculté agreed to it in 1780, perhaps Mesmer would have taken part in a trial, provided it was organized on the lines he proposed. However, his proposals to the Faculté run counter to the views that he explained vehemently in the Précis as those that he held after the Faculté's rejection. His position in 1781 was that the usefulness of his ‘discovery’ should only be judged on the basis of attested reports of the results of his treatment of patients and not on the results of experiments carried out for the purpose of testing the theory.12 Thus by 1781 Mesmer was insisting that any trial of the effectiveness of his treatment should be retrospective whereas in 1780 he was clearly proposing a prospective trial. No doubt these views, as well as his complete unwillingness to allow his methods to be examined, explain Mesmer's refusal to take part in the later trials. Indeed, it was not Mesmer's application of animal magnetism but Deslon's that was examined by the commissions of enquiry of 1784.13

The Royal Commissioners of 1784, however, took a different view. They were well aware that many patients reported dramatic effects from ‘animal magnetism’ and that many claimed that their symptoms were relieved by it. They deliberately avoided trying to determine by experiment if the treatment was effective because they were well aware of the difficulties of ascribing ‘cure’ to a particular treatment—they point out that many diseases resolve with no treatment and many different treatments may apparently produce ‘cures’.14 In short, they felt that this question was unanswerable.

The Commissioners chose a different question to which they believed their experiments could provide an unequivocal answer. The aim of their experiments was to discover whether there was any evidence for the mysterious properties that Mesmer called ‘animal magnetism’. A negative answer to this question would, in their minds, settle the question of their efficacy in treatment also, since, if the ‘magnetic’ properties did not exist, the question of whether they were effective in treatment simply could not arise.15

The Commissioners had themselves been ‘magnetized’ by Mesmer's associate Deslon, but felt no effects. Next, they tested subjects who had reported dramatic effects from ‘magnetization’ and were thus considered susceptible to it. They found that these subjects reported dramatic effects when presented either with ‘magnetized’ objects or with non-magnetized ones that they believed to have been magnetized. They also found that a typical crise, held to be induced by magnetism, consisting mostly of autonomic nervous responses and often culminating in convulsions, could be induced in such susceptible individuals merely by suggesting that ‘magnetization’ had taken place. On the other hand, the same subjects were unaware that they had been ‘magnetized’ when this was done without their knowledge. These and other experiments led the Commission to the conclusion that animal magnetism did not exist and that its purported effects must be ascribed to ‘the imagination’.

The Royal Commissioners anticipated that Mesmer would deny that his animal magnetism was the same as Deslon's and therefore were prudent enough to state explicitly at the end of their report that they expected him to make just such a denial and that, in advance, they dismissed it as baseless. Their expectations were fulfilled; when the Royal Commission found that there was no basis for belief in the existence of animal magnetism, Mesmer made exactly this denial saying it was Deslon's practice and not his that had been examined and been found to have no basis. One might summarize the difference between the Commissioners' outlook and that of Mesmer by saying that Mesmer was interested in a trial of whether his method had worked for patients as evidenced only by reports of the outcome of treatment, whereas the Commissioners were concerned primarily with whether there was a physical basis on which the method could work. The interpretation of the Commissioners' findings is quite complex and requires detailed discussion. There is a fuller account of the findings of the Royal Commission in my article in the James Lind Library.



AcknowledgmentThis paper was previously published by the James Lind Library []. Accessed 25 October 2005.


Images of the original text of Mesmer's proposals for the trial together with English translations and some other relevant material will be found on The James Lind Library []


1Deslon (1780; Reference 2) tried to persuade Mesmer that he would be better to use the popularity of his treatment with ‘the people’ to persuade the savants of its merits than to try, as Mesmer wished, to seek endorsement from the learned societies and thus to influence the opinion of the populace. Events proved Deslon right. For more details of Mesmer's quarrels with the learned societies, see references 1 & 4.

2For more details of this period in Mesmer's time in Paris see my Commentary in the James Lind Library [] (in preparation) on the Report of the Royal Commission set up in 1784 to examine Animal Magnetism.

3Most of the eighteenth century authors on Animal Magnetism refer to ‘Deslon’ but Mesmer himself calls him ‘d'Eslon’ which is how he appears in the title of his own book (reference 2). Deslon was a physician to the Comte d'Artois, one of Louis XVI's brothers. Born in 1750, he was only 30 when he wrote his book on Animal Magnetism and he died in 1786, the year in which Mesmer finally left Paris.

4Eslon, Charles d'. Observations sur le magnétisme animal. 1780 Reference 2.

5Eslon, Charles d'. Observations sur le magnétisme animal. 1780 Reference 2.

6See the original text and English translation of Mesmer's proposals in The James Lind Library [].

7See my article on Van Helmont's proposed trial in the James Lind Library (in preparation).

8Except, perhaps, in the case of a trial where only the effect of a remedy on one or a small number of symptoms (for example, pain, nausea) is to be tested without regard to the underlying pathology giving rise to the symptoms.

9Deslon is quoted as claiming that there is only ‘one Nature, one illness, one remedy; and that this remedy is Animal Magnetism’. Reference 6 p3.

10Mesmer FA. Reference 4. Avis au public, vj.

11See my article on Van Helmont's proposed trial in the James Lind Library (in preparation).

12For example, speaking of arrangements for the examination that he wished the government to make of his ‘discovery’ Mesmer says:

That the government could name Commissioners, not to examine my methods, not to negotiate with me, but to take note of attested facts and report on them. Reference 4 p. 195

And, more extravagantly, describing negotiations on the same subject with the principal Royal doctor, M. de Lassonne:

Here is what I said to M. de Lassonne; however bizarre [it may seem] at first sight it is nevertheless entirely serious and very much applicable to the question. When a thief is convicted of theft he is hanged: when a murderer is convicted of murder he is executed on the wheel. But to exact these terrible penalties the thief is not required to thieve again to prove that he is a thief, and the murderer is not required to murder a second time to prove that he is a murderer. One is content to establish by testimony and by material evidence that the theft or the murder was committed and then one hangs or executes on the wheel in good conscience.

Very well! It is the same with me. I ask, kindly, to be treated like a man to be executed on the wheel or hanged and that an effort should be made to establish that I have cured [patients] without asking me to perform new cures to prove that I am to be regarded as someone who cures. Reference 4 p. 196

See my commentary on the Report of the Royal Commission for more details.

13For example, The Royal Commission of 1784; Reference 5.

14Reference 5 pp. 11-15 (my translation in James Lind Library pp. 6-8).

15Reference 5 p. 8 (my translation in James Lind Library p. 5).


1. Bertrand A. Du magnétisme animal en France: et des jugements qu'en ont portés les sociétés savantes; avec le texte des divers rapports faits en 1784 par les commissaires de l'Académie des sciences, de la Faculté et de la Société royale de médicine...; suivi de considérations sur l'apparition de l'extase, dans les traitements magnétiques. Paris: JB Baillière, 1826
2. Eslon, Charles d'. Observations sur le magnétisme animal. London (and Paris): Didot/Saugrain/Clousier, 1780
3. Mesmer FA. Mémoire sur la découverte du magnétisme animal. Par M. Mesmer, Docteur en Médecine de la Faculté de Vienne. Geneva (and Paris): Didot le Jeune, 1779
4. Mesmer FA. Précis historique des faits relatifs au magnétisme animal jusques en avril 1781. Par M. Mesmer, Docteur en Médecine de la Faculté de Vienne. Ouvrage traduit de l'Allemand. London [sic. false imprint, probably Paris], 1781
5. Rapport des commissaires chargés par le Roi, de l'examen du magnétisme animale. Imprimé par ordre du Roi. Paris: L'Imprimerie Royale, 1784

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