Claudius Galenus was a Greek philosopher and physician who practiced medicine among the Romans circa AD 160. Galen brought the approach known as Humourism to the mainstream. Humourism is a philosophical theory originating from he Greek philosopher Empedocles who implied that all things are combinations of the four basic elements: earth, water, fire and air.
Excess black: prompted depression (or melancholy, literally black (melass) bile (khole) and cancer: oily, viscous, dark.
Cancer was believed to be the static form of black accumulating into a solid mass (ibid), whereas depression was viewed as the excess of fluid black bile circulating through the system.
Galen's falsely held beliefs about anatomy stood uncorrected until Andreas Vesalius's attempts to confirm his heroes hypothesis disconfirmed it. Due to Vesalius discontent with the state of anatomical training at the University of Paris, he began to his own exploratory autopsies (ibid). These exploratory autopsies on the bodies left at the city gallows and in poorly covered graces, revealed to Vesalius that the possibility of Galen's theories were non-existent. Blood, yellow bile and phlegm were found aplenty but black bile (the corner stone to Galen's theory) was no where to be found (ibid). Vesalius's discoveries and intricate anatomical drawings soon shattered the idea of humourism, opening up the doors to effective treatment.
The theory of Humourism, did not however completely disappear. In fact, in psychology a major theory of personality still owes its root to the Greek physicians.
Mukherjee, Siddhartha. The Emperor of All Maladies: A Biography of Cancer. New York: Scribner., 2010. Print.