Erasistratos, his colleague, was perhaps even a more successful investigator than Herophilos. He represented the best tradition of Greek medicine of the time. He had two distinguished teachers, one of them Metrodoros, the son-in-law of Aristotle. It was probably through this influence that Erasistratos received his invitation from the first Ptolemy to come to Alexandria. The scientific work of Alexandria was founded on Aristotle's collections, on his books, for his library was brought to Alexandria as the foundation of the great University Library, and then best of all on the direct tradition of his scientific teaching through this pupil of his son-in-law. Erasistratos' other great teacher was the well-known Chrysippos of Cnidos. Cnidos was the great rival medical school to that of Cos. Owing to the reputation of Hippocrates we know of Cos, but we must not ignore Cnidos. Erasistratos' discoveries were more in connection with the heart than anything else. He came very near discovering the circulation. His description of the valves and of their function is very clear. He looked for large-sized {386} anastomoses between veins and arteries and, of course, did not discover the minute capillaries which required Malpighi's microscope to reveal them nearly 2,000 years after. Like Herophilos, Erasistratos also studied the brain very faithfully. One story that we have of Erasistratos deserves to be in the minds of young graduates in medicine, because it illustrates the practical character of the man and also how much more important at times it may be in the practice of medicine to know men well rather than to know medical science alone. Erasistratos was summoned on a consultation to Antioch to see the son of King Seleucus. Seleucus was one of the four of Alexander's generals who, like Ptolemy, had divided the world among them after the young conqueror's death. His portion of the Eastern world, with its capital at Antioch, was probably the richest region of that time. There had been no happiness, however, in the royal household for months because the scion of the Seleucidae, the heir to the throne, was ill and no physician had been able to tell what was the matter with him, and, above all, no one had been able to do anything to awaken him from a lethargy that was stealing over him, making him quite incapable of the ordinary occupations of men, or to dispel an apathy which was causing him to lose all interest in affairs around him. He was losing in weight, he looked miserable, he seemed really to have been stricken by one of {387} the serious diseases as yet undifferentiated at that time which were expressed by the word phthisis, which referred to any wasting disease.