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The horizontal fraction bar was introduced by the Arabs.
It is believed that the Incas used anesthesia. Evidence supports the theory that shamans chewed cocoa leaves and drilled holes into the heads of patients (letting evil spirits escape), spitting into the wounds they made. The mixture of cocaine, saliva, and resin numbed the site enough to allow hours of drilling.
The familiar sounds of your heart are made by the heart's valves as they open and close.
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).
The U.S. Preventive Services Task Force recommends that all women age 65 years of age or older should be screened with bone densitometry.