from the isagoge of johannitius:

"the spirits are three in number: the first the natural spirit, having its origin from the liver; the second the vital spirit, having its origin from the heart; the third is animal spirit, having its origin from the brain. of these three the first is diffused throughout the body by means of the veins with no pulse; the second is diffused throughout the body by the heart; the third through the agency of the nerves by the brain."

you know you could write poems from the things you learn from medieval medical treatises.