Asclepius, the son of Apollo and Coronis, learned the secrets of keeping death at bay after observing one serpent bringing another (which Asclepius himself had fatally wounded) back to life with healing herbs. To prevent the entire human race from becoming immortal under Asclepius's care, Zeus killed him with a bolt of lightning. Asclepius' death at the hands of Zeus illustrates man's inability to challenge the natural order that separates mortal men from the gods. In honor of Asclepius, snakes were often used in healing rituals. Non-poisonous snakes were left to crawl on the floor in dormitories where the sick and injured slept. The "Bibliotheca" claimed that Athena gave Asclepius a vial of blood from the Gorgons. Gorgon blood had magical properties: if taken from the left side of the Gorgon, it was a fatal poison; from the right side, the blood was capable of bringing the dead back to life. However, Euripides wrote in his tragedy "Ion" that the Athenian queen Creusa had inherited this vial from her ancestor Erichthonios, who was a snake himself and had received the vial from Athena. In this version the blood of Medusa had the healing power while the lethal poison originated from Medusa's serpents.