What was Galen's theory of the natural faculties?
My central doctrine posits three 'natural faculties': nutrition, growth, and reproduction. These faculties, driven by the 'natural spirit' originating in the liver, are responsible for the body's fundamental processes. Nutrition draws in and processes food, transforming it into the body's substance. Growth then allows for an increase in size and strength, and reproduction ensures the continuation of the species. Each faculty operates with an inherent purpose, aiming at the preservation and propagation of the organism.