Galen himself, and apparently other physicians, were not content to rely for medicines either upon the unguent-sellers or the bounty of the imperial stores. Galen stored away oil and fat and left them to age until he had enough to last for a hundred years, including some from his father’s lifetime. He used some forty years old in one prescription.[567] He also traveled to many parts of the Roman Empire and procured rare drugs in the places where they were produced. Very interesting is his account of going out of his way in journeying back and forth between Rome and Pergamum in order to stop at Lemnos and procure a supply of the famous _terra sigillata_, a reddish clay stamped into pellets with the sacred seal of Diana.[568] On the way to Rome, instead of journeying on foot through Thrace and Macedonia, he took ship from the Troad to Thessalonica; but the vessel stopped in Lemnos at Myrine on the wrong side of the island, which Galen had not realized possessed more than one port, and the captain would not delay the voyage long enough to enable him to cross the island to the spot where the _terra sigillata_ was to be found. Upon his return from Rome through Macedonia, however, he took pains to visit the right port, and for the benefit of future travelers gives careful instructions concerning the route to follow and the distances between stated points. He describes the solemn procedure by which the priestess from the neighboring city gathered the red earth from the hill where it was found, sacrificing no animals, but wheat and barley to the earth. He brought away with him some twenty thousand of the little discs or seals which were supposed to cure even lethal poisons and the bite of mad dogs. The inhabitants laughed, however, at the assertion which Galen had read in Dioscorides that the seals were made by mixing the blood of a goat with the earth. Berthelot, the historian of chemistry, believed that this earth was “an oxide of iron more or less hydrated and impure.”[569] In another passage Galen advises his readers, if they are ever in Pamphylia, to lay in a good supply of the drug _carpesium_.[570] In the ninth book of his work on medicinal simples he tells of three strata of sory, chalcite, and misy, which he had seen in a mine in Cyprus thirty years before and from which he had brought away a supply, and of the surprising chemical change which the misy underwent in the course of these years.[571] [Sidenote: Mediterranean commerce.]