See Galen In Hipp. de nat. hom. comm. 15.136.2 ff. A prolific writer whose preserved works run to more than 12,000 pages, Galen wrote on philosophy as well as medicine. Many of his works were lost during his own lifetime, in a great fire around Rome’s Temple of Peace in 192 AD. The TLG Canon lists 109 titles that survive (at least in fragmentary form) in Greek. For a survey of his survival and influence, see Temkin 1973 and V. Nutton in OCD3.