[19] Again, the body-guards of the soul are hearing, and seeing, and smelling, and taste, and the whole band of the outward senses, and also health, and strength, and vigour, and energy. For the mind, when walking among and living in the company of these things, as between well-fortified boundaries firmly standing and solidly established, triumphs and rejoices, meeting with no hindrance on any side to prevent it from exerting its own impulses, but having its road in every direction easy, and level, and open, and easy to be travelled.