187. Margarite: i.e. pearls; this stone is cold and dry, and it is found in shells; the way it grows is, when the shell-fish swallows, it takes in a lot of the heavenly dew, and it closes around it, so that the stone is formed that is called the pearl. The pearl which has a natural hole in it is best, if it be white in colour; it has the virtue of comforting the heart, and they are put in comforting electuaries called diamargariton. Take note, if you wish the pearl to be white, give it to eat to a pet pidgeon, allow it in her stomach for three or four hours, then open the bird and take the stone out, and it will be clean, bright and shiny after that.