Daguerreotype showing a hypnotist with four subjects under hypnosis, 1845. John Adams Whipple (American, 1822-1891). During the early years of the daguerreotype, hypnosis was extensively practiced by reputable physicians in Europe and America. Although hypnotism eventually became associated with black magic and the supernatural, scientific interest in the phenomenon dates back to the late sixteenth century. Its therapeutic use both as a form of anesthesia and as a cure for disease was known from the 1830s. In 1848 the anesthetic properties of chloroform ended widespread medical practice of hypnotism, and it soon drifted back to marginal uses and quackery. This curious daguerreotype demonstrates the procedural method and medical theory of magnetic sleep, which held that a magnetic fluid emanated from an operator to a patient; through it, suggestions could be made directly to the subject's mind and indirectly through the mind upon the body. John Whipple, a Boston scientist, was one of the first suppliers of chemicals to American daguerreotypists.