(AD 23-79) Pliny the Elder, a Roman writer, once wrote "The arteries have no sensation, for they even are without blood, nor do they all contain the breath of life; and when they are cut only the part of the body concerned is paralyzed...the veins spread underneath the whole skin, finally ending in very thin threads, and they narrow down into such an extremely minute size that the blood cannot pass through them nor can anything else but the moisture passing out from the blood in innumerable small drops which is called sweat."
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(Aprox. AD 100) Galen, a Greek physician taught his students that there were two distinct types of blood. 'Nutritive blood' was thought to be made by the liver and carried through veins to the organs, where it was consumed. 'Vital blood' was thought to be made by the heart and pumped through arteries to carry the "vital spirits".
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(1535) You go to the physician with fatigue problems. He checks you out and notices your liver is larger. He thinks of one thing... eat your greens.
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William Harvey was made court physician to both King James I and King Charles at around AD 1600.
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His observations of dissected hearts showed that the valves in the heart allowed blood to flow in only one direction. Direct observation of the heartbeat of living animals showed that the ventricles contracted together, dispelling Galen's theory that blood was forced from one ventricle to the other.
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Thus concludes the history of the Circulatory System.
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Medicine did make some advances, for it was around AD 1600 that administering medicine through intravenous injections came into practice.
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Harvey's work raised more questions than it answered. For example, if blood was not consumed by organs, how did different parts of the body obtain nourishment? If the liver did not make blood from food, where did blood originate? These questions, and others like them, directed the research of many investigations for many years to come.
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