... with reference to its special origin and thus we attribute to it also a qualitative character. In separating libidinous from other psychic energy we give expression to the assumption that the sexual processes of the organism are differentiated from the nutritional processes through a special chemism. The analyses of perversions and psychoneuroses have taught us that this sexual excitement is furnished not only from the so-called sexual parts alone but from all organs ... — Three Contributions to the Theory of Sex • Sigmund Freud
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