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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.
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.
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.
Lower drug doses for elderly patients should be used first, with titrations of the dose as tolerated to prevent unwanted drug-related pharmacodynamic effects.
The first-known contraceptive was crocodile dung, used in Egypt in 2000 BC. Condoms were also reportedly used, made of animal bladders or intestines.