In psychoanalysis, the proposition that the quantity of psychic energy within the mental apparatus remains constant, regulation being achieved through discharge of excess energy in abreaction and avoidance of increase through defence mechanisms. This economic concept is derived loosely from the first law of thermodynamics, the conservation of energy law, and may be thought of as a form of homeostasis, but the formulations of it by the Austrian physician Josef Breuer (1842–1925) in Studies on Hysteria (1895, Standard Edition, II, at pp. 183–252) and by Sigmund Freud (1856–1939) in his book Beyond the Pleasure Principle (1920, Standard Edition, XVIII, pp. 7–64, especially at pp. 9, 55–6) are ambiguous and contradictory; in particular, Freud appears to confuse the regulation of energy with its reduction. See also bound energy, ego libido, free energy, hydraulic theory, metapsychology, object libido, quota of affect. Compare nirvana principle.