c. 340-280 BC

Praxagoras was a Greek natural scientist and anatomist. He followed a logical or dogmatic school of medicine. Praxagoras's famous pupil was Herophilus who established the Alexandrian School of medicine.

Praxagoras built upon humor theory, extending the traditional four humors to eleven. Like the other Greek physicians, he believed health and disease were controlled by the balance or imbalance of these humors. Praxagoras portrayed digestion as a kind of putrefaction or decomposition, an idea that lasted through the 18th century.

Praxagoras improved upon Aristotle's view of anatomy by distinguishing between arteries and veins. He saw arteries as air tubes, similar to the trachea and bronchi, which carried pneuma, the mystic force of life. Arteries, he theorized, took the breath of life from the lungs to the left side of the heart through the aorta to the arteries of the body.

When modeling the blood and pneuma systems Praxagoras held that the arteries carried pneuma and that the veins carried blood. Further, he portrayed the arteries as stemming from the heart and the veins from the liver. The combination of blood and pneuma generated heat. Thick, cold phlegm if gathered in the arteries would result in either paralysis or epilepsy.

Along Aristotle and Diocles, Praxagroas subscribed to a cardio-centric view of the body. He saw the heart as the central organ of intelligence and the seat of thought. He differed from the others, however, in that he believed the purpose of respiration was to provide nourishment for the psychic pneuma, rather than to cool the body's inner heat.

Praxagoras was the first to direct attention to the importance of arterial pulse in diagnosis. He thought that arteries pulsed by themselves and were separate from the heart. Herophilus, his student, refuted this doctrine in his treatise "On Pulses."

The theories of Praxagoras's were influential and long-lasting. Nearly 500 years after his death, people still believed that arteries contained pneuma rather than blood.