in the early 1900s a major use of Tesla coils was to apply high frequency current directly to the body in electrotherapy.
Tesla invented tech still used today, in modified forms. Some things he never realised in his lifetime like the 'death ray'. One of the conspiracy theories out there is that HAARP was using his research to produce a non-leathal weapon that is perfected today, that uses radio waves to cause 'brain-fog' in living beeings over vast areas. And that tests with this weapon is what causes whales to beach, and birds to drop from the sky.