Phlegm occupies a revealing, if rarely central, position in the depth-psychology corpus. It enters primarily through two distinct conduits: the ancient humoral tradition, in which phlegm constitutes one of the four bodily fluids whose balance determines temperament and disease, and the alchemical tradition, where it figures as a quality—the cold, moist, viscous—associated with the albedo, the lunar, and the sluggishness inherent even in the highest mental operations. Plato’s Timaeus, a foundational source for both lines, treats phlegm as a product of bodily corruption, generated when flesh wastes into the veins, and as the specific cause of defluxion-diseases and, crucially, of the ‘sacred disease’ of epilepsy. Hillman’s alchemical psychology reconstellates this material most provocatively, arguing that phlegm is the necessary shadow of silver’s brilliance—the ‘phlegmatic leprosy’ that accompanies intellectual activity, legitimising leisure as a structural companion to the life of the mind. Place and Miller locate phlegm within the fourfold humor-typology that Jung inherited and then critically distanced himself from, noting that Jung found the temperamental schema phenomenologically inadequate. Ruth Padel traces the medical-flux imagery that gave phlegm its cosmological weight in Greek tragic thought. The tension across the corpus is between phlegm as pathological surplus to be expelled and phlegm as a psychologically necessary, even redemptive, principle of inertia.