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Hippocrates noted that blood separates into four differently colored liquids when removed from the body and examined: a pure red liquid mixed with white liquid material with a yellow-colored froth at the top and a black substance that settles underneath; he named these the four humors (for blood, phlegm, yellow bile, and black bile).
Most childhood vaccines are 90–99% effective in preventing disease. Side effects are rarely serious.
In the ancient and medieval periods, dysentery killed about ? of all babies before they reach 12 months of age. The disease was transferred through contaminated drinking water, because there was no way to adequately dispose of sewage, which contaminated the water.
More than 150,000 Americans killed by cardiovascular disease are younger than the age of 65 years.
There are 20 feet of blood vessels in each square inch of human skin.
![The conduction system of the heart; traces the path of the electrical impulse that stimulates the he](https://biology-forums.com/gallery/47/medium_14755_10_09_12_7_22_09_85202259.jpeg)
![An electrocardiogram (EKG) wave, a record of the electrical signal as it moves through the conductio](https://biology-forums.com/gallery/47/medium_14755_10_09_12_7_22_09_85211006.jpeg)