A serpent entwined round a knotted staff is the symbol of Æsculapius. A humorist of the present day has suggested that the knots on the staff indicate the numerous "knotty" questions which a doctor is asked to solve! Tradition states that when Æsculapius was in the house of his patient, Glaucus, and deep in thought, a serpent coiled itself around his staff. Æsculapius killed it, and then another serpent appeared with a herb leaf in its mouth, and restored the dead reptile to life. It seems probable that disease was looked upon as a poison. Serpents produced poison, and had a reputation in the most ancient times for wisdom, and for the power of renovation, and it was thought that a creature which could produce poison and disease might probably be capable of curing as well as killing. Serpents were kept in the Temples of Æsculapius, and were non-poisonous and harmless. They were given their liberty in the precincts of the temple, but were provided with a serpent-house or den near to the altar. They were worshipped as the incarnation of the god, and were fed by the sick at the altar with "popana," or sacrificial cakes. [Illustration: From Wellcome's Medical Diary (Copyright) By permission of Burroughs Wellcome & Co. Plate II.--HYGEIA The Greek Deity of Health.] Many of the Greek gods and goddesses were held to have power over disease. Hygeia, known as Salus to the Romans, was said to have been the daughter of Æsculapius, and to have taken care of the sacred serpents (Plate II). Melampus was considered by the Greeks the first mortal to practise healing. In one case he prescribed rust, probably the earliest use of iron as a drug, and he also used hellebore root as a purgative. He married a princess and was given part of a kingdom as a reward for his services. After his death he was awarded divine honours, and temples were erected for his worship. The deification of Æsculapius and of Melampus added much to the prestige of doctors in Greece, where they were always held in honour; but in Rome the practice of medicine was not considered a highly honourable calling.