It would be a very difficult matter to furnish here, within a limited space, a reasonably clear exposition of the views held by Hippocrates with regard to human physiology and pathology. Empedocles, a Greek physician and high priest of Agrigentum, in Sicily, who was born about 490 B. C., founded a system of philosophy on the theory that the universe is made up of four elements--fire, air, earth and water; and he maintained that fire is the essence of life, the other elements forming the basis of matter. It was upon this system that Hippocrates founded his own theories of life, death and disease, but he disagreed with Empedocles in regard to the manner in which the four elements are united, his own belief being that they form together a genuine mixture, whereas Empedocles maintains that their union represents merely a mechanical aggregation of separate atoms. He also held that these original four elements, to which he gave the names of heat, cold, dryness and moisture, were represented in the human body by the following four cardinal fluids or “juices”: blood, mucus or phlegm, black bile and yellow bile.[25] He maintained, further, that when these elements are mingled harmoniously so as to produce a state of perfect equilibrium, health resulted; but that when some deficiency of one or more of them, or some lack of harmony between them in other respects, occurs, disease is produced. At a later date, a fifth element--wind or air (pneuma)--was added to the other four; and when Hippocrates was unable to account satisfactorily for certain phenomena of disease, he was wont to refer the phenomenon observed to divine interference. This brief exposition of the physiological and pathological views held by Hippocrates, incomplete and superficial as it is, will have to suffice. Those who wish to acquire a more profound knowledge of the subject should consult some of the larger treatises like those of Daremberg, of Max Neuburger, and of Pagel, as well as the sections devoted to these subjects in the French (Littré) and the German (Fuchs) versions of the Hippocratic writings. At every step in such a study, the modern physician will encounter ideas and individual terms which he will have great difficulty in comprehending; and later on, as he reads the sections which deal with the more practical matters of the medical art, he will be astonished to find that Hippocrates was a most acute and trustworthy observer of the phenomena of disease, a remarkably clear writer, and a standard-bearer of very high aims.