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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.
Ether was used widely for surgeries but became less popular because of its flammability and its tendency to cause vomiting. In England, it was quickly replaced by chloroform, but this agent caused many deaths and lost popularity.
Blood is approximately twice as thick as water because of the cells and other components found in it.
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.
There are over 65,000 known species of protozoa. About 10,000 species are parasitic.

