Two men, however, more commonly ranked among philosophers than among physicians of antiquity, dissected the statements of Hippocrates, and embodied them more or less in their own teachings, and thus exercised a great influence on the progress of the human mind, particularly in the direction of medical study. The first of these was Plato, profound moralist, eloquent writer, and most versatile thinker of his day or any other. He undertook the study of disease, not by observation (the empirical or experimental method), but by pure intuition. He seemed to have never discovered that his meditations were taken in the wrong direction, and that the method did not conduce to the discovery of abstract truths. He gave beauty an abstract{ 028} existence, and affirmed that all things beautiful are beautiful because of the presence of beauty. This reminds one of that famous response in the school of the Middle Ages to a question: "Why does opium produce sleep?" the answer being: "Because it possesses the sleepy principle." Plato introduced into natural science a doctrine of final causes. He borrowed from Pythagoras the dogma of homogeneity of matter, and claimed that it had a triangular form.
_Aristotle_, equally great thinker with Plato, but whose mental activity was manifest in other channels, was born in Stagyrus, in Macedonia. He was fascinated by the teachings of Plato, and attained such eminence as a student that King Philip of Macedon made him preceptor to his son Alexander, subsequently the Great, by whom he was later furnished with sufficient funds to form the first known museum in natural history.--a collection of rare objects of every sort, transmitted, many of them, by the royal hands of his former student from the remote depths of Asia. Aristotle, by long odds the greatest naturalist of antiquity, laid the first philosophic basis for empiricism. He admitted four elements--fire, air, earth, and water--and believed them susceptible of mutual transmutation. He studied the nature of the soul and that of the animal body; regarded heat and moisture as two conditions indispensable to life; described the brain with some accuracy, but without the least idea of its true function; said that the nerves proceeded from the heart; termed the aorta a nervous vein; and made various other mistakes which to us seem inexcusable. Nevertheless, he was rich in many merits, and no one of his age studied or searched more things than he, nor introduced so many new facts. Although he never dissected human bodies, he nevertheless corrected errors in anatomy held to by the Hippocratic school. He dissected a large number of animals of every species, and noted the varieties of size and shape of hearts of various animals and birds. In{ 029} other words, he created a comparative anatomy and physiology, and the plan that he traced was so complete that two thousand years later the great French naturalist Cuvier followed it quite closely. If he be charged with having propagated a taste for scholastic subtleties, he also furnished an example of patient and attentive observation of Nature. His history of animals is a storehouse of knowledge, and his disciples cultivated with zeal anatomy, physiology, and natural history. His successor, Theophrastus, was the most eminent botanist of antiquity.