The spleen is given to Saturn in the western scheme, and again the reasoning is humoral: the spleen was held in Galenic physiology to be the seat of black bile, the melancholic humour, cold and dry, and Saturn is the cold and dry planet. The vocabulary again survives in English, where to vent one's spleen means to give way to ill temper, and splenetic means irritable, though the humoral sense was pensive and sorrowful rather than angry. This is the same association that produced, by way of Ficino's Renaissance reading of the Aristotelian Problemata, the enduring link between melancholy and creative genius. In Chinese medicine the spleen, pi, belongs to the earth phase, governs the transformation of food into qi and blood and the holding of blood within the vessels, and is associated with worry and overthinking.
Ayurveda pairs the spleen closely with the liver under Ranjaka Pitta, the same blood-colouring subdosha noted above, and classical Ayurvedic anatomy, rooted in the Sushruta Samhita, counted the spleen, pliha, among the organs governing the blood tissue, dhatu, rather than assigning it an independent function of its own. The organ's western reputation for melancholy, noted above from Galenic humoral theory, produced a lasting medical assumption: splenectomy, its surgical removal, was long thought to carry serious risk to mood and temperament precisely because of that old association, an assumption modern medicine has not upheld, since the spleen's real functions are immunological and haematological rather than emotional.
Sources Christian AstrologyWilliam Lilly with The Roots of Ayurveda: Selections from Sanskrit Medical WritingsDominik Wujastyk