Short answers, pulled from the story.
The four fluids in the humorism system are blood, phlegm, yellow bile, and black bile. These liquids were believed to dictate every thought, emotion, and physical ailment in the ancient Greek and Roman system of medicine.
Hippocrates systematized the theory of humorism between 460 and 370 BC. This work transformed medicine from a spiritual practice into a physiological one by arguing that these fluids were the fundamental building blocks of the human constitution.
Galen of Pergamum linked blood to spring and infancy, yellow bile to summer and youth, black bile to autumn and adulthood, and phlegm to winter and old age. This seasonal alignment dictated medical practice by suggesting that the nature of the humors waxed and waned with the changing weather.
Treatments included bloodletting, purging, emetics, and catharsis to expel surplus humor. The 16th-century Swiss physician Paracelsus further developed the idea that beneficial medical substances could be found in herbs, minerals, and alchemical combinations.
Black bile was considered the most detrimental humor because it was linked to depression, fear, and a sickly appearance. It was believed to cause cancer and was associated with the cold and dry characteristics of autumn.
The theory of humorism was not definitively disproven until 1858, when the list of temperament traits was finally defined. The dominance of humorism began to crumble in the 17th century as advances in cellular pathology and chemistry challenged the theory's core assumptions.