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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).
The human body produces and destroys 15 million blood cells every second.
Immunoglobulin injections may give short-term protection against, or reduce severity of certain diseases. They help people who have an inherited problem making their own antibodies, or those who are having certain types of cancer treatments.
The immune system needs 9.5 hours of sleep in total darkness to recharge completely.
Amoebae are the simplest type of protozoans, and are characterized by a feeding and dividing trophozoite stage that moves by temporary extensions called pseudopodia or false feet.