of life. Arteries took the breath of life from the lungs to the left side of the heart through the aorta to the arteries of the body. He believed the arteries stemmed from the heart, but the veins came from the liver. Veins carried blood, which was created by digested food, to the rest of the body. The combination of blood and pneuma generated heat. As one of the humors, thick, cold phlegm gathered in the arteries would cause paralysis. Also, he believed that arteries were the channels through which voluntary motion was given to the body, and that the cause of epilepsy was the blocking of the aorta by this same accumulation of phlegm. Aristotle, Diocles, and Praxogoras insisted that the heart was the central organ of intelligence and the seat of thought. Praxagoras differed with the others in that he believed the purpose of respiration was to provide nourishment for the psychic pneuma, rather than to cool the inner heat. Arteries and pulse Praxagoras' views on arteries were very influential in the development of physiology. Since the concept of nerves did not exist, Praxagoras explained the movement of arteries to the fact that arteries get smaller and smaller, and then disappear. This disappearance caused movement, a fact now attributed to nerves. However, he speculated about the role of movement and was satisfied that he had found the answer of the center of vitality and energy. His pupil, Herophilus, actually discovered both sensory and motor nerves. Praxagoras was interested in pulse and was the first to direct attention to the importance of arterial pulse in diagnosis. He insisted that arteries pulsed by themselves and were independent of the heart. Herophilus refuted this doctrine in his treatise "On Pulses." In another area, Galen criticized Praxagoras for displaying too little care in anatomy. He suggested that Praxagoras did not arrive at his theories by dissection. The beliefs of Praxagoras held sway for centuries. For example, for nearly 500 years after his death, many still believed that arteries did not contain blood but pneuma. His most famous pupil, Herophilus, was instrumental in establishing the marvelous medical establishment at Alexandria. See also Galen Hippocrates William Harvey Marcello Malpighi References Vivian Nutton, "Ancient Medicine" New York: Routledge, 2004. External links Ancient Greek Medicine 4th-century BC Greek physicians Ancient Koans Year of death unknown 340s BC births