In his treatise _On Ancient Medicine_, he says that men first learned from experience the science of dietetics; they were compelled to ascertain the properties of vegetable productions as articles of food. Then they learned that the food which is suitable in health is unsuitable in sickness, and thus they applied themselves to the discovery of the proper rules of diet in disease; and it was the accumulation of the facts bearing on this subject which was the origin of the art of medicine. “The basis of his system was a rational experience, and not a blind empiricism; so that the empirics in after ages had no good grounds for claiming him as belonging to their sect.”[389] He assiduously applied himself to the study of the natural history of diseases, especially with the view to determine their tendencies to death or recovery. In every case he asked himself what would be the probable end of the disorder if left to itself. Prognosis, then, is one of the chief characteristics of Hippocratic medicine. He hated all charlatanism, and was free from all popular superstition. When we reflect on the medicine of the most highly civilized nations which we have considered at length in the preceding pages, and remember how full of absurdities, of magic, amulet lore, and other things calculated to impose on the credulity of the people, were their attempts at healing, we shall be inclined to say, that the most wonderful thing in the history of Hippocrates was his complete divorce from the evil traditions of the past. Although he forsook philosophy as an ally of medicine, his system was founded in the physical philosophy of the elements which the ancient Greeks propounded, and which we have attempted to explain. There was an all-pervading spiritual essence which is ever striving to maintain all things in their natural condition; ever rectifying their derangements; ever restoring them to the original and perfect pattern. He called that spiritual essence Nature. “Nature is the physician of diseases.”[390] Here, then, we have the enunciation of the doctrine of the _Vis Medicatrix Naturæ_. In his attempts to aid Nature, the physician must regulate his treatment “to do good, or at least, to do no harm”;[391] yet he bled, cupped, and scarified. In constipation he prescribed laxative drugs, as mercury (not the mineral, of course, but _Mercurialis perennis_), beet, and cabbage, also elaterium, scammony, and other powerful cathartics. He used white hellebore boldly, and when narcotics were required had recourse to mandragora, henbane, and probably to poppy-juice. He is said to have been the discoverer of the principles of derivation and revulsion in the treatment of diseases.[392]