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There are over 65,000 known species of protozoa. About 10,000 species are parasitic.
Most childhood vaccines are 90–99% effective in preventing disease. Side effects are rarely serious.
Vaccines cause herd immunity. If the majority of people in a community have been vaccinated against a disease, an unvaccinated person is less likely to get the disease since others are less likely to become sick from it and spread the disease.
Blood in the urine can be a sign of a kidney stone, glomerulonephritis, or other kidney problems.
Hippocrates noted that blood separates into four differently colored liquids when removed from the body and examined: a pure red liquid mixed with white liquid material with a yellow-colored froth at the top and a black substance that settles underneath; he named these the four humors (for blood, phlegm, yellow bile, and black bile).