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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 average human gut is home to perhaps 500 to 1,000 different species of bacteria.
Alzheimer's disease affects only about 10% of people older than 65 years of age. Most forms of decreased mental function and dementia are caused by disuse (letting the mind get lazy).
The Babylonians wrote numbers in a system that used 60 as the base value rather than the number 10. They did not have a symbol for "zero."
Your skin wrinkles if you stay in the bathtub a long time because the outermost layer of skin (which consists of dead keratin) swells when it absorbs water. It is tightly attached to the skin below it, so it compensates for the increased area by wrinkling. This happens to the hands and feet because they have the thickest layer of dead keratin cells.
![Diabetes mellitus. The metabolic disease diabetes mellitus, with symptoms of polydipsia, polyuria, a](https://biology-forums.com/gallery/47/medium_14755_14_10_12_6_35_06_93842397.jpeg)
![Urinalysis. During a simple urinalysis, a stick with colored blocks is dipped into a urine specimen.](https://biology-forums.com/gallery/47/medium_14755_26_10_12_5_21_07_96732306.jpeg)