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The immune system needs 9.5 hours of sleep in total darkness to recharge completely.
The first successful kidney transplant was performed in 1954 and occurred in Boston. A kidney from an identical twin was transplanted into his dying brother's body and was not rejected because it did not appear foreign to his body.
There are over 65,000 known species of protozoa. About 10,000 species are parasitic.
In 1864, the first barbiturate (barbituric acid) was synthesized.
An identified risk factor for osteoporosis is the intake of excessive amounts of vitamin A. Dietary intake of approximately double the recommended daily amount of vitamin A, by women, has been shown to reduce bone mineral density and increase the chances for hip fractures compared with women who consumed the recommended daily amount (or less) of vitamin A.