ABSTRACT
THE psychological investigation of abnormal mental states may be said to have begun when Mesmer induced the scientific world to examine the phenomena of Animal Magnetism. Previous to this time, although unusual or disordered states of mind had often been observed and described, a psychology which was solely dependent on introspection could make little progress in elucidating their nature; for the peculiarities of mental process which they displayed seemed to have little in common with anything the psychologist could discover in his own mind. Moreover, most of these states were met with only occasionally, they occurred only spontaneously, and they were often of short duration, so that any investigation undertaken was brought to an abrupt end with the termination of the abnormal condition. But when a means of inducing “magnetic trance” was discovered, an abnormal state, well deserving examination, could be brought about at will, and the first requisite of the experimental method—ability to repeat the experiment—was secured. It may be said that all our knowledge of the psychology of the abnormal can be traced to its beginnings in the study of artificially induced trance states.
