Out of the teachings of Plato and Aristotle developed two schools of philosophy that exerted, in course of time, a great influence upon the minds of men and upon the growth of medical science. The schools referred to are the Epicureans and the Stoics. Epicurus (242–270 B. C.), who gave his name to the first of these, taught that the highest good was happiness. The happiness he taught his followers to seek was not sensual enjoyment, but peace of mind as the result of the cultivation of all the virtues. According to the teaching of his school virtue should be practiced _because_ it leads to happiness; whereas the Stoics taught that virtue should be cultivated for her own sake, irrespective of the happiness it will ensure. Zeno (circa 370–260 B. C.), the founder of the Stoic philosophy, taught an ethical system according to which virtue consists in absolute judgment, absolute mastery of desire, absolute control of the soul over pain, and absolute justice. The keynote of the system is _duty_, as that of Epicureanism is pleasure. (Sir William Smith.) In addition to the sects named above, there was still another known as the Older Dogmatic School, which was composed of men who had been the direct followers of the great master, but who, forgetting altogether the practical teachings of Hippocrates with regard to the importance of experience, gave themselves up to all sorts of hypotheses and theories. Among the names of the earliest followers of this school one is astonished to find those of Thessalus and Draco, the sons of Hippocrates, as well as the name of Polybus, the latter’s son-in-law. Diocles of Carystos and Praxagoras of Cos, two of the most distinguished men of that period, were also among the earliest members of this dogmatic school. Diocles, who was one of the Asclepiadae, owed his celebrity in part to his contributions to our knowledge of anatomy and in part to the work which he had done in other departments of medicine. Unfortunately, all of these writings have been lost with the exception of a few fragments which came to light toward the middle of the nineteenth century. Praxagoras was also one of the Asclepiadae. He was distinguished, as has already been stated on an earlier page, by the fact that he--and not Aristotle, as is sometimes stated--was first to recognize the difference between arteries and veins, and also by the further fact that he called attention to the practical value of the pulse as an indication, in certain diseases, of the tone of the patient’s bodily condition or vitality. CHAPTER X ERASISTRATUS AND HEROPHILUS, THE TWO GREAT LEADERS IN MEDICINE AT ALEXANDRIA; THE FOUNDING OF NEW SECTS