Animal magnetism, also known as mesmerism, was the name given by the German doctor Franz Mesmer in the 18th century to what he believed to be an invisible natural force (lebensmagnetismus) possessed by all living/animate beings (humans, animals, vegetables, etc.). He believed that the force could have physical effects, including healing. He tried persistently but without success to achieve scientific recognition of his theories.
The vitalist theory attracted numerous followers in Europe and the United States and was popular into the 19th century. Practitioners were often known as magnetizers, rather than mesmerists. For about 75 years from its beginnings in 1779 it was an important specialty in medicine, and continued to have some influence for about another 50 years. Hundreds of books were written on the subject between 1766 and 1925. Today it is almost entirely forgotten.
Mesmerism is still practised as a form of alternative medicine in some countries, but magnetic practices are not recognized as part of medical science, and are considered by many medical scientists and practitioners to work by self-suggestion through the universal process known as response expectancy.
The terms "magnetizer" and "mesmerizer" have been applied to people who study and practice animal magnetism. These terms have been distinguished from "mesmerist" and "magnetist", which are regarded as denoting those who study animal magnetism without being practitioners; and from "hypnotist", someone who practises hypnosis.
The etymology of the word magnetizer comes from the French "magnetiseur" ("practicing the methods of mesmerism"), which in turn is derived from the French verb magnetiser. The term refers to an individual who has the power to manipulate the "magnetic fluid" with effects upon other people present that were regarded as analogous to magnetic effects. This sense of the term is found, for example, in the expression of Antoine Joseph Gorsas: "The magnetizer is the imam of vital energy".
A tendency emerged amongst British magnetizers to call their clinical techniques "mesmerism"; they wanted to distance themselves from the theoretical orientation of animal magnetism that was based on the concept of "magnetic fluid". At the time, some magnetizers attempted to channel what they thought was a magnetic "fluid", and sometimes they attempted this with a "laying on of hands". Reported effects included various feelings: intense heat, trembling, trances, and seizures.