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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.
After a vasectomy, it takes about 12 ejaculations to clear out sperm that were already beyond the blocked area.
In most cases, kidneys can recover from almost complete loss of function, such as in acute kidney (renal) failure.
When blood is exposed to air, it clots. Heparin allows the blood to come in direct contact with air without clotting.
Pope Sylvester II tried to introduce Arabic numbers into Europe between the years 999 and 1003, but their use did not catch on for a few more centuries, and Roman numerals continued to be the primary number system.