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Egg cells are about the size of a grain of sand. They are formed inside of a female's ovaries before she is even born.
Throughout history, plants containing cardiac steroids have been used as heart drugs and as poisons (e.g., in arrows used in combat), emetics, and diuretics.
The immune system needs 9.5 hours of sleep in total darkness to recharge completely.
Many people have small pouches in their colons that bulge outward through weak spots. Each pouch is called a diverticulum. About 10% of Americans older than age 40 years have diverticulosis, which, when the pouches become infected or inflamed, is called diverticulitis. The main cause of diverticular disease is a low-fiber diet.
Sperm cells are so tiny that 400 to 500 million (400,000,000–500,000,000) of them fit onto 1 tsp.