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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.
The first-known contraceptive was crocodile dung, used in Egypt in 2000 BC. Condoms were also reportedly used, made of animal bladders or intestines.
There are 20 feet of blood vessels in each square inch of human skin.
Complications of influenza include: bacterial pneumonia, ear and sinus infections, dehydration, and worsening of chronic conditions such as asthma, congestive heart failure, or diabetes.
In ancient Rome, many of the richer people in the population had lead-induced gout. The reason for this is unclear. Lead poisoning has also been linked to madness.