Then I dreamed that one day there was nothing but milk for them and the jailer said as he put down the pipkin: 'Our relations with the cow are not delicate-as you can easily see if you imagine eating any of her other secretions.' … John said, 'Thank heavens! Now at last I know that you are talking nonsense. You are trying to pretend that unlike things are like. You are trying to make us think that milk is the same sort of thing as sweat or dung.' 'And pray, what difference is there except by custom?' 'Are you a liar or only a fool, that you see no difference between that which Nature casts out as refuse and that which she stores up as food?'

Pilgrim's Regress 49 - The Pilgrim's Regress (1933)