The Irish physicians of old had a keen appreciation of the healing influences of incantations upon the minds of their patients, and the latter had moreover a strong faith in the ancient Druidic charms and invocations. It is probable that in very early times, invocations were made in the names of favorite pagan deities. After the introduction of Christianity by Saint Patrick, the name of the Trinity and the words of the Christian ritual were substituted. Such invocations, when repeated in the presence of sick persons, are regarded by the Irish peasants of to-day as powerful talismans, effective through their magic healing power. So great is the faith of these simple people in the ancient hereditary cures, that they prefer to seek medical aid from the wise woman of the village, rather than from a skilled practitioner.[40:1] The influence of the mind upon the physical organism, through the imagination, is well shown by the seemingly marvellous cures sometimes wrought by medical charms. But the efficacy of magical medicine has been usually proportionate to the degree of ignorance prevalent during any particular epoch. Yet some of the most famous physicians of antiquity had faith in superstitious remedies. The medical literature of the last century before Christ, and from that period until late in the Middle Ages, was an actual treasury of conjuration and other mummeries. Even the great Galen, who was regarded as an oracle, openly avowed his belief in the merits of magic cures.[41:1] Galen wrote that many physicians of his time were of the opinion that medicines lost much of their efficacy, unless prescribed by their Babylonian or Egyptian names. They fully appreciated mental influence as a factor in therapeutics. Hence, instead of regular prescriptions, they sometimes wrote mystic formulas, which their patients either carried as charms, or rolled into pellets, which were then swallowed.[41:2] In a "Book of Counsels to Young Practitioners" (1300) are to be found some interesting items regarding contemporary manners. Fledgling doctors are therein advised to make use of long and unintelligible words, and never to visit a patient without doing something new, lest the latter should say, "He can do nothing without his book." In brief, a reputation for infallibility must be maintained.