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Blood is approximately twice as thick as water because of the cells and other components found in it.
When blood is exposed to air, it clots. Heparin allows the blood to come in direct contact with air without clotting.
The Babylonians wrote numbers in a system that used 60 as the base value rather than the number 10. They did not have a symbol for "zero."
Human kidneys will clean about 1 million gallons of blood in an average lifetime.
Signs of depression include feeling sad most of the time for 2 weeks or longer; loss of interest in things normally enjoyed; lack of energy; sleep and appetite disturbances; weight changes; feelings of hopelessness, helplessness, or worthlessness; an inability to make decisions; and thoughts of death and suicide.