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Human stomach acid is strong enough to dissolve small pieces of metal such as razor blades or staples.
On average, the stomach produces 2 L of hydrochloric acid per day.
The immune system needs 9.5 hours of sleep in total darkness to recharge completely.
Human kidneys will clean about 1 million gallons of blood in an average lifetime.
People who have myopia, or nearsightedness, are not able to see objects at a distance but only up close. It occurs when the cornea is either curved too steeply, the eye is too long, or both. This condition is progressive and worsens with time. More than 100 million people in the United States are nearsighted, but only 20% of those are born with the condition. Diet, eye exercise, drug therapy, and corrective lenses can all help manage nearsightedness.