It is due to the flow of bile. Melancholy is a state of persistent fear, i.e continuous flow of bile. Grief and anxiety arise from brain cooling. It is due to the flow of phlegm. In normal states, corporeal elements are mixed in a balanced manner.
Pain results if one or several elements are disfunctional.
This is considered as the first biological theory of pain. Happiness is made of pleasure, utility and good. His disciples formally associated pleasure with good, and pain with evil. Please send us your comments.