Ectoplasm is a usually light-coloured gelatinous substance that exudes from the body of a Spiritualist medium during a seance, which the spirits being communicated with are able to mould into shapes allowing them to communicate with the living. It has also been known as ectoplasmic mass or teleplasmic mass, and is generally a slime that will be familiar to fans of the 1984 film Ghostbusters.
The word ectoplasm is derived from the Greek ektos, meaning “outside”, and plasma, meaning “something moulded”. The term was introduced in about 1894 by the Nobel prize-winning French physiologist Charles Richet, although at least one authority has attributed the term to the German physician Albert Freiherr von Schrenck-Notzing.
Early researchers such as Richet and Baron von Schrenck-Notzing were convinced of the reality of ectoplasm. In his Phenomena of Materialization (1920), Schrenck-Notzing asserted that
We have often been able to establish that by an unknown process there comes from the body of the medium a material, at first semi-fluid, which possesses some of the properties of a living substance …
A subsequent series of fraudulent exposures led to a decline in the popularity of so-called materialisation mediums, but there remain elements of the Spiritualist community who maintain a belief in ectoplasmic phenomena, despite the lack of credible evidence for their existence.