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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).
Sperm cells are so tiny that 400 to 500 million (400,000,000–500,000,000) of them fit onto 1 tsp.
After a vasectomy, it takes about 12 ejaculations to clear out sperm that were already beyond the blocked area.
Most childhood vaccines are 90–99% effective in preventing disease. Side effects are rarely serious.
Bacteria have flourished on the earth for over three billion years. They were the first life forms on the planet.

