Another early member of the Western school who made important contributions to medical doctrine--in which relation alone we need consider him--was Pythagoras of Samos (_c._ 580-_c._490 B. C.). For him number, as the purest conception, formed the basis of philosophy. Unity was the symbol of perfection and corresponded to God Himself. The material universe was represented by 2, and was divided by the number 12, whence we have 3 worlds and 4 spheres. These in turn, according at least to the later Pythagoreans, give rise to the four elements, earth, air, fire, and water--a primary doctrine of medicine and of science derived perhaps from ancient Egypt and surviving for more than two millennia. The Pythagoreans taught, too, of the existence of an animal soul, an emanation of the soul of the universe. In all this we may distinguish the germ of that doctrine of the relation of man and universe, microcosm and macrocosm, which, suppressed as irrelevant in the Hippocratic works, reappears in the Platonic and especially in the Neoplatonic writings, and forms a very important dogma in later medicine. A pupil of Pythagoras and an older contemporary of Empedocles was Alcmaeon of Croton (_c._ 500 B. C.), who began to construct a positive basis for medical science by the practice of dissection of animals, and discovered the optic nerves and the Eustachian tubes. He even extended his researches to Embryology, describing the head of the foetus as the first part to be developed--a justifiable deduction from appearances. Alcmaeon introduced also the doctrine that health depends on harmony, disease on discord of the elements within the body. Curiosity as to the distribution of the vessels was excited by Empedocles and Alcmaeon and led to further dissection, and Alcmaeon's pupils Acron (_c._ 480 B. C.) and Pausanias (_c._ 480 B. C.), and the later Philistion of Lokri,[64] the contemporary of Plato, all made anatomical investigations. [64] For the work of these physicians see especially M. Wellmann, _Fragmentsammlung der griechischen Aerzte_, Bd. I, Berlin, 1901.