This cursory background for people unfamiliar with the subject. Multiple online resources can be found for those interested in pursuing further information.
Franz Anton Mesmer, (1734 - 1815) a Austrian physician is credited with the discovery of Animal Magnetism, which is known for being the foundation for hypnosis. The development and support of hypnosis is perhaps what led to the demise of Mesmerism by over shadowing it in the Medical community, which never fully accepted Magnetism at the time. Though this lack of acceptance didn’t thwart the continued practice of Mesmerism, it severely crippled its development. It is perhaps that he revealed his discovery to soon. Before it was really understood. This left it in a rudimentary state for centuries. Science requires collaboration and competition to keep moving forward and create the opportunity for further discovery. Without this, Mesmerism has been consigned to the category of pseudo science or quackery, of little interest to all but alternative medicine enthusiasts. A key piece of research that is missing, is the effects of Mesmerism on the Mesmerizer. As Mesmer was a physician, his focus was, of course on healing. Other applications and developments were beyond the scope of his work and therefore probably not even considered. In China there is an age old practice called Chi Gung, roughly, Energy Work that is similar in outward appearance to Magnetism. The practitioners use movement and breathing techniques to cultivate and manipulate internal energy for health and healing. This is where the similarities end. Chi Gung practitioners tend to focus their energy on a single target point. The energy is thought to reside within the practitioner and projected outwards . In contrast, the Magnetizer passes their hand (magnetic field) through the magnetic field of the subject thus generating current flow. All very scientific in theory. Opponents like to point out that the electrical field of a human being is negligible. Proponents could quickly point to Chaos Theory which supports that making small alterations in any system causes wildly different behavior. A fixed bow with a fixed draw on a windless day, fires an arrow. It will land where it lands according to the amount of force generated by the bow, the weight of the arrow and the trajectory in accord with the tilt of the bow. An alteration of any of those factors by a fraction of an amount, will send the arrow, wildly off target. The effects of magnetism are not expected to be immediate. This is where it fails the scientific acid test. Science tends not to invest any time in things that don’t show immediate results and rightly so. The more time that passes between application and results, the more factors become involved that defy scrutiny. Without scrutiny science can’t responsibly confirm anything.

Franz Mesmer proposed that there is a magnetic fluid that is all pervasive and present in all life forms and their surroundings. The fact that we can’t see it or bottle it makes it difficult to prove the existence of this magnetic fluid. Compounding the issue of proof is language. When someone says magnetic we think of iron and several rare earths and their capacity to be magnetized and to transfer that magnetism to similar objects even across a visible distance. Magnetic flux can even be generated to such a magnitude that it can be seen by the unaided eye. The atomic structure of most other minerals protects them from being magnetized. Anyone interested in the how and why of magnetism of this sort can find details online. It is of no real interest to the subject of animal magnetism, beyond curiosity, as the magnetic fluid proposed by Mesmer is named such because it mimics magnetism. That’s where the confusion starts and where it should end. Mesmeric fluid mimics the behavior of magnetism. More on this later. So how to prove its existence? It was decided in Mesmer’s day that the proof rests in the results it produced. To this end subjects were treated and examined. However, there are no details as to how these subjects were selected. In this day and age, test subjects are generally required to pass a psychological exam before being eligible to participate. Largely due to the discovery of certain psychological disorders that compel some individuals to volunteer for anything. As well, they tell the researchers what they think they want to here. Then there are those individuals that are highly susceptible to hypnotic suggestion that has been estimated at five percent of the population. In Mesmer’s time, Sigmund Frued, the father of Psychoanalysis, hadn’t even been born. So the quality of the participants is suspect at best. Reported effects during treatments include a trance like state, even somnambulism. It has been reported that the French Academy of Science initially concluded that the effects of treatments were due to the subjects imagination or charlatanry. There was no denying the positive effects from the treatments and at the same time no proof of the existence of this magnetic fluid.
To this day it is maintained by many that the effects of mesmeric treatments come solely from within the individual and not some external transference of an occult substance. However it should be noted that there are substantial and significant differences between mesmerism and hypnosis. Where as the techniques of Mesmerism tend to entrance the subject, it is not the intent or even a desired effect.