Thirteen/WNET PBS

Blood History

Mirror of the Soul

For thousands of years, the human body was a mystery to the world of science. Indeed, cultures across the globe employed various forms of observation, experience, ritual, intuition, and other methods to combat illness; such efforts met with varying degrees of success. Yet profound exploration of human physiology remained elusive. Nowhere was this more apparent than in the understanding, or lack thereof, of blood -- what it is; what it does; where it flows; how it is created; and many other questions went unanswered. For many, one issue was clear: bloodletting was a sound medical procedure.

c. 2500 BCE: The Egyptians use bleeding to treat patients. A tomb illustration in Memphis, Egypt, depicts a patient being bled from the foot and neck.

c. 500 BCE: Greek thinker who practices animal dissection, Alcmaeon of Croton, observes that arteries and veins are dissimilar.

c. 450-400 BCE: Empedocles, a Greek philosopher in Sicily, believes that the organ of sense is the heart and theorizes that all matter is comprised of four "roots" (or elements) -- earth, fire, air, and water.

c. 400 BCE: Influenced by the ideas of Empedocles, Hippocrates, the preeminent physician of antiquity, postulates that similar to the four elements, the body is comprised of four humors -- blood, phlegm, black bile, and yellow bile -- and their imbalance causes disease. In addition to humoral theory, Hippocrates and his followers set forth tenets that form the basis of much of Western medicine: disease results from natural as opposed to magical causes, patients should be observed and symptoms of disease should be noted, and physicians should adhere to a strict ethical code of conduct.

c. 350 BCE: Greek philosopher Aristotle believes that the heart is the central organ of the body and therefore the seat of the soul. He conducts dissections of many different animals and describes their anatomical structures. Based on his observations, Aristotle presumes the heart is a three-chambered organ, even in humans. 300 BCE: In Alexandria, Egypt, one of the first Greek anatomists to publicly dissect human cadavers, Herophilus of Chalcedon, determines that arteries are thicker than veins and carry blood.

c. 130-200 BCE: Through his studies of anatomy, successful treatment of patients, and voluminous writings on medicine and the philosophy of medicine, Claudius Galenus, known as Galen, becomes one of the most important physicians in history, second only to Hippocrates in influence. Dissecting and experimenting on animals, he proves that arteries contain blood, but also suggests that the system of arteries and veins are completely distinct, and blood forms in the liver and travels through the veins to all parts of the body and passes between the ventricles through pores in the septum. His ideas, not all of which are correct, form the core of the medical canon for centuries.