HEROPHILUS, of Chalcedon in Bithynia, a pupil of CHRYSIPPUS of Cnidos and PRAXAGORAS of Cos, was one of the most famous physicians of the ancient world. He was a great anatomist and physiologist, and a contemporary of the philosopher Diodorus Cronos, and of Ptolemy Soter in the fourth and third centuries B.C. He settled at Alexandria, which under Ptolemy I. became the most famous centre of the science of the ancient Greeks. Here Herophilus founded with other physicians of the city the great medical school which ultimately became distinguished above all others, so that a sufficient guarantee of a physician’s ability was the fact that he had received his education at Alexandria. The foundation of the Alexandrian School formed a great epoch in the history of medicine. The dissection of the human body was of the utmost importance to the healing art. While the practice was forbidden, it could only have been performed furtively and in a hasty and unsatisfactory manner. The science of anatomy, on which that of medicine to be anything but quackery must be founded, now took its proper place in the education of the doctor. The bodies of all malefactors were given over for the purposes of dissection.[409] Herophilus is accused of having also dissected alive as many as six hundred criminals. This fact has been denied by some of his biographers, and others have attempted to explain it away; but it is charged against him by Tertullian,[410] and Celsus mentions it[411] as though it were a well-known fact, and without the least suspicion that it was an unjust accusation. Asked who is the best doctor, he is said to have replied, “He who knows how to distinguish the possible from the impossible.”