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There are over 65,000 known species of protozoa. About 10,000 species are parasitic.
Pubic lice (crabs) are usually spread through sexual contact. You cannot catch them by using a public toilet.
According to the American College of Allergy, Asthma & Immunology, more than 50 million Americans have some kind of food allergy. Food allergies affect between 4 and 6% of children, and 4% of adults, according to the CDC. The most common food allergies include shellfish, peanuts, walnuts, fish, eggs, milk, and soy.
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).
In most climates, 8 to 10 glasses of water per day is recommended for adults. The best indicator for adequate fluid intake is frequent, clear urination.