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The familiar sounds of your heart are made by the heart's valves as they open and close.
When Gabriel Fahrenheit invented the first mercury thermometer, he called "zero degrees" the lowest temperature he was able to attain with a mixture of ice and salt. For the upper point of his scale, he used 96°, which he measured as normal human body temperature (we know it to be 98.6° today because of more accurate thermometers).
It is important to read food labels and choose foods with low cholesterol and saturated trans fat. You should limit saturated fat to no higher than 6% of daily calories.
Cancer has been around as long as humankind, but only in the second half of the twentieth century did the number of cancer cases explode.
The average human gut is home to perhaps 500 to 1,000 different species of bacteria.