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Not getting enough sleep can greatly weaken the immune system. Lack of sleep makes you more likely to catch a cold, or more difficult to fight off an infection.
Autoimmune diseases occur when the immune system destroys its own healthy tissues. When this occurs, white blood cells cannot distinguish between pathogens and normal cells.
There used to be a metric calendar, as well as metric clocks. The metric calendar, or "French Republican Calendar" divided the year into 12 months, but each month was divided into three 10-day weeks. Each day had 10 decimal hours. Each hour had 100 decimal minutes. Due to lack of popularity, the metric clocks and calendars were ended in 1795, three years after they had been first marketed.
There are 20 feet of blood vessels in each square inch of human skin.
Approximately 500,000 babies are born each year in the United States to teenage mothers.