Through the writings of Aulus Cornelius Celsus (25 B.C.-?), the Roman encyclopedist, and Galen (ca. A.D. 130-200) venesection was restored as a form of orthodox medical treatment and remained so for the next fifteen hundred years. By the time of Celsus, bloodletting had become a common treatment. Celsus remarked in his well-known account of early medicine: "To let blood by incising a vein is no novelty; what is novel is that there should be scarcely any malady in which blood may not be let."[5] Yet criticism of bloodletting continued, for when Galen went to Rome in A.D. 164 he found the followers of Erasistratus opposing venesection. Galen opened up discussion with these physicians in two books, _Against Erasistratus_ and _Against the Erasistrateans Dwelling in Rome_. These argumentative dialectical treatises, together with his _Therapeutics of Venesection_, in which he presented his theory and practice of venesection, established Galen's views on bloodletting, which were not effectively challenged until the seventeenth century.[6] The fundamental theory upon which explanations of health and disease were based, which had its inception in ancient Greek thought and lasted up to the eighteenth century, was the humoral theory. Based on the scientific thought of the Pre-Socratics, the Pythagoreans, and the Sicilians, this theory posited that when the humors, consisting of blood, phlegm, yellow bile, and black bile, were in balance within the body, good health ensued. Conversely, when one or more of these humors was overabundant or in less than adequate supply, disease resulted. The humors were paired off with specific qualities representing each season of the year and the four elements according to the well-accepted doctrine of Empedocles, in which all things were composed of earth, air, fire, and water. Thus, yellow bile, fire, and summer were contrasted to phlegm, water, and winter, while blood, air, and spring were contrasted to black bile, earth, and autumn. When arranged diagrammatically, the system incorporating the humors, elements, seasons, and qualities appears as shown in Figure 1. The earliest formulation of humoralism was to be found in the physiological and pathological theory of the Hippocratic treatise, _On the Nature of Man_.[7] Plethora, an overabundance of body humors, including blood, which characterized fevers and inflammations, was properly treated by encouraging evacuation. This could be done through drugs that purged or brought on vomiting, by starvation, or by letting blood. During starvation the veins became empty of food and then readily absorbed blood that escaped into the arteries. As this occurred, inflammation decreased. Galen suggested that instead of starvation, which required some time and evacuated the system with much discomfort to the patient, venesection should be substituted to remove the blood directly.[8]