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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).
There are more bacteria in your mouth than there are people in the world.
There are approximately 3 million unintended pregnancies in the United States each year.
A cataract is a clouding of the eyes' natural lens. As we age, some clouding of the lens may occur. The first sign of a cataract is usually blurry vision. Although glasses and other visual aids may at first help a person with cataracts, surgery may become inevitable. Cataract surgery is very successful in restoring vision, and it is the most frequently performed surgery in the United States.
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.
![History of the number of observed sunspots during the last 250 years, which shows the ~11-year solar](https://biology-forums.com/gallery/47/medium_12359_16_06_12_7_11_02.png)
![Endocarditis. The human heart has been sectioned to reveal the left ventricle and origin of the aort](https://biology-forums.com/gallery/47/medium_14755_11_11_12_7_14_26_100221543.jpeg)