What is the line which indicates the Doctor subscribes to the medieval idea of the Four Humours and what are the four Humours.

The term humor refers to the four fluids of the human body: phlegm, blood, yellow bile, and black bile. Being sick would mean they the humors are imbalanced,

He knew the cause of every sickness,
Whether it brings heat or cold, moisture or dryness,
And where engendered, and of what humour;
He was a very good practitioner.