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Blood is a viscous fluid that flows slower than water.
All About Blood
The main organ of blood circulation is the heart, a very powerful and
precise muscle that pumps constantly to keep our blood flowing. Blood
flowing away from the heart is usually rich in oxygen and under the great-
est pressure. Arteries are muscular blood vessels that carry blood away from
the heart to the tissues of the body. After the blood has released its load of
oxygen, it flows back toward the heart through the veins. Thinner walled
than arteries, veins are not usually under quite the same amount of pres-
