Always select tender beans. Break the blossom end, and pull it backward, removing the string. Then be careful to pare the thin strip from the other end of the Bean pod. It is only in this way that you will be sure that every inch of string is removed. Split the larger Beans down the pod, and let the younger and more tender remain whole. Wash them in clear, cold water, letting them stand about ten minutes. Then drain off the water, put the Beans into a saucepan, cover well with boiling water, and let boil for forty minutes or an hour, according to the tenderness of the Beans. Just before serving drain off water, add butter to the Beans, mix well, salt and pepper to taste, and serve hot.