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Human neurons are so small that they require a microscope in order to be seen. However, some neurons can be up to 3 feet long, such as those that extend from the spinal cord to the toes.
More than 2,500 barbiturates have been synthesized. At the height of their popularity, about 50 were marketed for human use.
Human stomach acid is strong enough to dissolve small pieces of metal such as razor blades or staples.
Increased intake of vitamin D has been shown to reduce fractures up to 25% in older people.
Although the Roman numeral for the number 4 has always been taught to have been "IV," according to historians, the ancient Romans probably used "IIII" most of the time. This is partially backed up by the fact that early grandfather clocks displayed IIII for the number 4 instead of IV. Early clockmakers apparently thought that the IIII balanced out the VIII (used for the number 8) on the clock face and that it just looked better.