The Four Humors come from Hippocrates' theory that the health of a person, both 

mental and physical, is governed by a combination of fluids in the body: blood, yellow

bile, phlegm, and black bile (yuck!).  When the fluids are in balance, the ancient Greek

postulated, the body and mind are in balance.  Should a fluid come to predominate, the 

following would occur:

 

I.  Cholericus--Too much choler, or yellow bile.  This person would act angry, violent and vengeful.

 

II  Melancholicus--The person with too much black bile would be gloomy and sad.

 

III.  Flematicus--With too much phlegm, one was cold, emotionless (and probably in need of a tissue).

 

IV.  Sanguinicus--An over-abundance of blood wrought cheerfulness and optimism.