18.  Place and time and age and season and the like are the subjects of a physician’s scrutiny; he will prescribe medicines and diet, and guard against things injurious, that the desires of the sick may not be a hindrance to his art.  Sometimes, and in certain cases, he will make use of the cautery or the knife or the severer remedies; but none of these, laborious and hard as they may seem, is so difficult as the diagnosis and cure of our habits, passions, lives, wills, and whatever else is within us, by banishing from our compound nature everything brutal and fierce, and introducing and establishing in their stead what is gentle and dear to God, and arbitrating fairly between soul and body; not allowing the superior to be overpowered by the inferior, which would be the greatest injustice; but subjecting to the ruling and leading power that which naturally takes the second place:  as indeed the divine law enjoins, which is most excellently imposed on His whole creation, whether visible or beyond our ken.