The sources from which Aristotle drew the material of his philosophical science were therefore (1) his inherited taste for medicine and empirical science; and (2) the influence of the Academy in ethical, metaphysical, and cultural subjects. Both these factors appear throughout the philosophical development of Aristotle. On the other hand, it must not be forgotten that probably Aristotle’s influence upon the Academy was as great as that of the Academy upon him. His own persistence along the line of empirical science shows itself in his period at Atarneus, Mitylene, and on his return to Stagira. Much has been said about an estrangement between Aristotle and his teacher, Plato. This is probably idle gossip. Aristotle held his master in great esteem, as he himself testifies in his _Ethics_. Aristotle was an independent and original mind, and probably even in the school he would point out defects in Plato’s thought, when his aged teacher would lead his theories upon mistaken lines. Plato said that his pupil Xenocrates needed the spur, while Aristotle needed the bridle. Aristotle was called the brain of the Academy. =2. Second Period=, 347–335 B. C.――=Traveler and Collector=. When Plato died, and his nephew Speusippus became scholarch of the Academy, Aristotle, in company with Xenocrates, went to the court of Hermeias, ruler of Atarneus and Mitylene. Hermeias was another pupil of Plato at the Academy. Here Aristotle married twice, and here he resided for six years. In 343 B. C. he obeyed the summons of King Philip to come to Pella and become the tutor of Alexander. He acted in this capacity for four years, and seems to have been more fortunate than Plato as instructor of a king. His influence upon Alexander was very great. Without losing himself in the impracticable, Aristotle seems to have impressed high philosophical ideals upon the noble spirit of his kingly ward. Alexander says of Aristotle, “To my father I owe my life, to Aristotle the knowledge how to live worthily.” During the tedium of the protracted campaign in Bactria, Alexander sent for the tragedies of Euripides, Sophocles, and Æschylus. The _Ethics_ of his teacher was always with him. The ideals of statesmanship, the wide purposes in political control, the greatness of the aims of the young conqueror, as well as his self-control, his aversion to meanness and petty things, and his sublime moderation were due in part to the teachings of Aristotle. Never was there a more fortunate conjunction of two great minds than here.