Full Idea
Galen ran medicine on the principle of the mean; afflictions must be treated by contraries; hot diseases deserve cold medicine and moist illnesses want drying agents. (Paracelsus rebelled, treating through similarity).
Gist of Idea
Galen's medicine followed the mean; each illness was balanced by opposite treatment
Source
report of Galen (On Medical Experience [c.169]) by Ian Hacking - The Emergence of Probability Ch.5
Book Reference
Hacking,Ian: 'The Emergence of Probability' [CUP 1975], p.42
A Reaction
This must be inherited from Aristotle, with the aim of virtue for the body, as Aristotle wanted virtue for the psuché. In some areas Galen is probably right, that natural balance is the aim, as in bodily temperature control.