_Claudius Galenus_, commonly known as Galen, has influenced the progress of medical science by his writings probably more than any other medical writer. His influence was paramount for fourteen centuries, and although he made some original contributions, his works are noteworthy mainly as an encyclopædia of the medical knowledge of his time and as a review of the work of his predecessors. There is a great deal of information in his books about his own life. He was born at Pergamos in A.D. 130 in the reign of Hadrian. His father was a scholar and his mother somewhat of a shrew. Galen, in his boyhood, learned much from his father's example and instruction, and at the age of 15 was taught by philosophers of the Stoic, Platonist, Peripatetic, and Epicurean schools. He became initiated, writes Dr. Moore, into "the idealism of Plato, the realism of Aristotle, the scepticism of the Epicureans, and the materialism of the Stoics." At the age of 17 he was destined for the profession of medicine by his father in consequence of a dream. He studied under the most eminent men of his day. He went to Smyrna to be a pupil of Pelops, the physician, and Albinus the platonist; to Corinth to study under Numesianus; to Alexandria for the lectures of Heraclianus; and to Cilicia, Phœnicia, Palestine, Crete, and Cyprus. At the age of 29 Galen returned from Alexandria to Pergamos (A.D. 158), and was appointed doctor to the School of Gladiators, and gained much distinction. He went to Rome for the first time in A.D. 163-4, and remained for four years; and during this period he wrote on anatomy and on the teaching of Hippocrates and Plato. He acquired great fame as a practitioner and, if he had so desired, might have attended the Emperor; but it is probable that Galen thought that the office of physician to the Emperor might prevent him from leaving Rome if he wished to do so. He also gave public lectures and disputations, and was called not only the "wonder-speaker" but the "wonder-worker." His success gave rise to envy, and he was afraid of being poisoned by his less successful rivals. The reason why he left Rome is not certain, and the possible causes of his departure are discussed by Dr. Greenhill in the "Dictionary of Greek and Roman Biography and Mythology." A pestilence raged in Rome at this time, but it is unlikely that Galen would have deserted his patients for that reason. Probably he disliked Rome, and longed for his native place. He had been in Pergamos only a very short time when he was summoned to attend the Emperors Marcus Aurelius and L. Verus in Venetia. The latter died of apoplexy on his way home to Rome, and Galen followed Marcus Aurelius to the capital. The Emperor soon thereafter set out to prosecute the war on the Danube, and Galen was allowed to remain in Rome, as he had stated that such was the will of Æsculapius. The Emperor's son Commodus was placed under the care of Galen during the father's absence, and at this time also (A.D.