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Sperm cells are so tiny that 400 to 500 million (400,000,000–500,000,000) of them fit onto 1 tsp.
The first-known contraceptive was crocodile dung, used in Egypt in 2000 BC. Condoms were also reportedly used, made of animal bladders or intestines.
Hyperthyroidism leads to an increased rate of metabolism and affects about 1% of women but only 0.1% of men. For most people, this increased metabolic rate causes the thyroid gland to become enlarged (known as a goiter).
People with high total cholesterol have about two times the risk for heart disease as people with ideal levels.
During the twentieth century, a variant of the metric system was used in Russia and France in which the base unit of mass was the tonne. Instead of kilograms, this system used millitonnes (mt).