The professional physicians, who, even in later times, regarded their art as divine, and handed down by their ancestor Aesculapius (on which account they also called themselves _Asklepiadae_), were probably a development from the priestly physicians. It is very likely that in the first centuries after Homer, the practice of the medical art was still directly connected with the worship of Aesculapius, and that the separation which we find in the historic period, where some remained as medical assistants to the priests in the sanctuaries, and others practised independently on their own account, only gradually made way. It cannot be a mere chance that the places where the most celebrated medical schools of antiquity existed, Cos and Cnidus, were also regarded as the chief seats of the worship of Aesculapius. The professional physicians, who practised their art independently, and were not connected with the sanctuaries, naturally received a fee, and though this brought them into somewhat bad repute, with which every art that conduced to making money was regarded, yet their occupation stood in much higher general estimation than any of the trades, and it was a serious reproach if they, as sometimes happened, insisted on receiving their payment beforehand, and in case of inability to pay, refused to give any treatment at all. Their knowledge was not acquired at colleges or hospitals, like that of our modern physicians, but, as a rule, they became assistants or apprentices to old experienced physicians, whom they accompanied on their visits, and by whom they were instructed in diagnosis and therapeutics, as well as in the preparation of medicines. There were sellers of drugs, who kept the most important remedies, but there were no apothecaries in our modern sense, and physicians always prepared their own medicines. There does not appear to have been any examination necessary in early times before practising the medical profession, or any direct control or supervision of the doctors, but in later times physicians seem to have held together in a sort of guild, and, perhaps, even solemnly dismissed their apprentices at the end of their period of instruction before their assembled colleagues. This is suggested by the oath of Hippocrates, which has been preserved to us, in which the young disciple of Aesculapius promises to keep only the welfare of his patient before him, to keep silence, to give no one poison, even at his own request, etc. Probably this oath was only used in the school of Hippocrates and his followers.