Mescal: The 'Divine' Plant and Its Psychological Effects

Mescal: The 'Divine' Plant and Its Psychological Effects is a 1928 book about the peyote and its effects by the German–American physiological psychologist and philosopher Heinrich Klüver.^[1][2][3][4] Peyote contains the psychedelic drug mescaline.^[5][6]

Klüver studied the subjective and perceptual effects of peyote at the University of Chicago by administering it to several subjects and to himself.^[1][7][8] His research described in the book includes the first phenomenological description of the psychedelic experience as well as the systematic analysis of hallucinogen-induced geometrical images.^[8] He worked with peyote rather than Merck's mescaline (available since 1920) as the former was easier to source.^[1] Klüver found that peyote produced recurring geometric patterns with remarkable uniformity across individuals.^[8] He referred to these patterns as "form constants" and categorized them into four groups, including lattices, cobwebs, tunnels, and spirals.^[8][1][9] Form constants were Klüver's most enduring contribution to cognitive psychology.^[1] Besides these visual phenomena, Klüver also described other types of visual effects, such as brightened colors, increased contrast, and perceptions of movement or motion, as well as synaesthesia.^[1][9][10] In addition, he described emotional and psychological effects of peyote, for instance its noetic qualities.^[1] Klüver's work built on the observations of earlier researchers like Silas Weir Mitchell and Havelock Ellis.^{[3][1][11][12]}

Mescal: The 'Divine' Plant and Its Psychological Effects was the first book or scientific monograph on peyote or mescaline to be published in English.^{[1][13][7][3]} It reviewed the existing literature and introduced the English-speaking world to the German research on the drug.^[1][2][3] Richard Evans Schultes was inspired to study psychoactive plants by the book, which he had obtained from the Harvard Botanical Museum and read.^[1][3] Other researchers have expanded on Klüver's work, for instance Ronald Siegel extending his form constants from four types to nine.^[10][14][15]

Klüver later published a book chapter called Mechanisms of Hallucinations in 1942.^[10][13][16] He then combined both Mescal: The 'Divine' Plant and Its Psychological Effects (1928) and Mechanisms of Hallucinations (1942) into a single title known as Mescal and Mechanisms of Hallucinations and published this in 1966.^{[1][13][10][17]} This combined and reprinted version had a psychedelic-themed jacket and greatly outsold the original 1928 monograph.^[1] One other relevant publication is Klüver's 1926 journal article Mescal Visions and Eidetic Vision.^[2][13][18] This article attracted the attention of Charles Kay Ogden and MacDonald Critchley and led to Klüver's 1928 book being written.^[13]