• According to El Sevier's Dictionary of Psychological Theories, Hippocrates, a well-known Greek physician, and Empedocles, a philosopher, were the first ones to expand on the theory of the four humors. However, related observations had already been made before Hippocrates developed his theory.
• This theory is based on the four elements (water, earth, fire, and air) and how each one corresponds to specific qualities. In the case of earth, it is cold and dry, while fire is warm and dry. Meanwhile, water is cold and moist, while air is warm and moist.
• Furthermore, each element is involved in a specific humor, represented by cardinal fluids, which in turn leads to a temperament when these fluids are not balanced. In the case of earth, it was linked to black bile, which corresponded to the melancholic temperament. Air was linked to blood, which would lead to a sanguine temperament; water corresponded to phlegm, and it was associated with a phlegmatic temperament, while fire was associated with yellow bile, corresponding to a choleric temperament.
• It is important to highlight that while Hippocrates proposed the theory of the four humors (black bile, yellow bile, blood, and phlegm), it was Galen who went one step further and turned it into the theory of the four temperaments. 

Artistic Representations

• The Rijksmuseum is home to Choleric, a print of an engraving representing one of the four temperaments, which was created between the 16th and 17th centuries. Melancholic, and Phlegmatic are also pieces by the same artists, which are present in this museum.
• Another artwork alluding to the temperaments is a painting made by Daniel Nikolaus Chodowieki. The piece is titled "The Effects of Sensitivity on the Four Different Temperaments", and it was created around 1767.
• In 1946, George Balanchini choreographed a ballet inspired by the four humors or temperaments. The four movements of the ballet were hence called Choleric, Phlegmatic, Melancholic, and Sanguine.
• According to the United States National Library of Medicine, Shakespeare included the theory of the four humors in his work, including The Taming of the Shrew, Hamlet, and The Merchant of Venice.

Book Titles

• One of the books detailing the four temperament theory is "The Four Temperaments: A Rediscovery of the Ancient Way of Understanding Health and Character", written by Randy Rolfe.
• A second book that highlights this theory is titled "Passions and Tempers: A History of the Humors", written by Noga Arikha.

Studies

• There are studies that have focused on the theory of the four humors, from its origin to its validity.
• One of these studies is titled "Concept of Akhlat Arba (four humors) with relation to health and disease", and it proposes that although Hippocrates summarized the theory, this was already studied in Mesopotamia.
• Another study titled "A Reconstruction of the Hippocratic Humoral Theory of health" aimed to present the full theory developed by Hippocrates.

Diagrams

• An interesting diagram represents the relationship between the four humors, temperaments, and how food can be used to balance these humors in the body.

Summary of Findings

• During our initial hour of research, we focused on assessing the availability of the information and providing initial findings for each of the requested types of sources (book titles, studies, diagrams, and artistic representations), with a special focus on artistic representations . We could provide additional information with further research.