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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).

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Although puberty usually occurs in the early teenage years, the world's youngest parents were two Chinese children who had their first baby when they were 8 and 9 years of age.

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It is difficult to obtain enough calcium without consuming milk or other dairy foods.

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Bacteria have flourished on the earth for over three billion years. They were the first life forms on the planet.

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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.

Menstrual cycle summary based on a 28-day (average) menstrual cycle. Menstrual cycle summary based on a 28-day (average) menstrual cycle.
(a) Mean duration (days) and (b) average maximum depth (mm) of snow cover throughout northern latitu (a) Mean duration (days) and (b) average maximum depth (mm) of snow cover throughout northern latitu
Killer Whale - Size comparison to an average human. Killer Whale - Size comparison to an average human.
Average Global Temperature during the Phanerozoic Average Global Temperature during the Phanerozoic
Examples of Impacts Associated with Different Amounts of Global Average Temperat Examples of Impacts Associated with Different Amounts of Global Average Temperat
The Clean Development Mechanism allows developed countries The Clean Development Mechanism allows developed countries
Video: Introduction to Human Immunodeficiency Virus (HIV)

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