Ever since its discovery, electricity has been used for therapeutic purposes. Electrostatic charges developed by stroking an amber rod with a silk cloth were experimented as far back as the 16th century.
The first notable experiments were probably conducted by Friedrich Anton Mesmer (1733-1815). These involved stroking the body with magnets and other means of delivering gauss to the body. He did this to good effect and became famous, treating lords, nobles and monarchs. Since science had not as yet progressed to the point of any theory as to how this might work, Mesmer’s experiments were largely un-repeatable and was eventually declared a fraud by Benjamin Franklin
That didn’t stop the fascination of experimenters with the fundamental principals of electro-medicine to go unabated. By 1890, an electro-medical society was founded in the U.S.
Literally hundreds of electrical devices of every conceivable shape and configuration were available to the public. A fair portion of these devices did have the potential of doing the job they were intended for, all with differing theories, and many with totally ridiculous claims. It was not until much later that the effects were understood.
Around the beginning of the 20th century, Albert Abrams did further experiments, developing machines to do the work; but again, the inadequacies of good scientific theory led to unexplained failures, and Abrams too was eventually discredited.
During the 1930s, the medical industry went through a big change, during which, most electro-medical devices were shunned or disregarded. It was the worst possible time in history to present scientific evidence that electro-medicine had value.