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The immune system needs 9.5 hours of sleep in total darkness to recharge completely.
More than 2,500 barbiturates have been synthesized. At the height of their popularity, about 50 were marketed for human use.
Cancer has been around as long as humankind, but only in the second half of the twentieth century did the number of cancer cases explode.
There are 60,000 miles of blood vessels in every adult human.
The human body produces and destroys 15 million blood cells every second.
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