^ Joseph Jastrow. (1935). Patience Worth: An Alter Ego in Wish and Wisdom: Episodes in the Vagaries of Belief. D. Appleton-Century Company. pp. 78–92. Lyon Sprague de Camp. (1966). Spirits, Stars, and Spells. New York: Canaveral. p. 247. Robert Goldenson. (1973). Mysteries of the Mind: The Drama of Human Behavior. Doubleday. pp. 44–53. Milbourne Christopher. (1970). ESP, Seers and Psychics. New York: Crowell. pp. 128–29
In the 1930s Harry Price (director of the National Laboratory of Psychical Research) had investigated the medium Helen Duncan and had her perform a number of test séances. She was suspected of swallowing cheesecloth which was then regurgitated as "ectoplasm". Price had proven through analysis of a sample of ectoplasm produced by Duncan, that it was made of cheesecloth. Helen Duncan would also use a doll made of a painted papier-mâché mask draped in an old sheet which she pretended to her sitters was a spirit. The photographs taken by Thomas Glendenning Hamilton in the 1930s of ectoplasm reveal the substance to be made of tissue paper and magazine cut-outs of people. The famous photograph taken by Hamilton of the medium Mary Ann Marshall depicts tissue paper with a cut out of Arthur Conan Doyle's head from a newspaper. Skeptics have suspected that Hamilton may have been behind the hoax.
In the late 1920s and early 1930s there were around one quarter of a million practising Spiritualists and some two thousand Spiritualist societies in the UK in addition to flourishing microcultures of platform mediumship and 'home circles'. Spiritualism continues to be practised, primarily through various denominational Spiritualist churches in the United States, Canada, Australia and the United Kingdom. In the United Kingdom, over 340 Spiritualist churches and centres open their doors to the public and free demonstrations of mediumship are regularly performed.