The human figure in the centre is derived from the tarot
The diagram shows the four elements as defined by ancient Greek philosophers (air, water, earth, fire) and the four qualities which they combine: air combines the hot and the wet, water the cold and the wet, earth the cold and the dry, fire the hot and the dry. These are then used to define the four humours (humors): blood has the qualities of fire, making people sanguine (cheerful); phlegm the qualities of water, making people phlegmatic; black bile the qualities of earth, making people melancholic; and yellow bile the qualities of fire, making people choleric (hot tempered). Each temperament is boosted by the associated season or age of life, or diminished by the opposite season or age of life. This system was the basis of traditional western medicine. Thus, someone with too much of the hot and wet will have too much blood, and may need bloodletting, especialy in spring, less so in winter when the cold and wet in the environment counteracts the hot and dry in the body, and even less in old age, which has more of the same qualities as winter
