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 Deslon) that there was only one disease and only one cure for it; in fact that animal magnetism was a universal panacea. 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 elsewhere—just a rhetorical device to support his arguments against the ‘Galenists’.