The laxative simples: indeed some of them such as scammony become weak on infusion, others such as myrobalan become concentrated, and some others such as cassia fistola become refined. For Constantinus says that every medicine which purges by its attractive force contains matter too poisonous and contrary to nature, so for this reason it is necessary for the physician when he administers it to do everything with reason and to administer it according to the virtue, season, appearance, and age; and to administer it in a safe and reasonable way so that the body may not change from its own complexion to another worse complexion, and may not die.