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When blood is exposed to air, it clots. Heparin allows the blood to come in direct contact with air without clotting.
After a vasectomy, it takes about 12 ejaculations to clear out sperm that were already beyond the blocked area.
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).
Acetaminophen (Tylenol) in overdose can seriously damage the liver. It should never be taken by people who use alcohol heavily; it can result in severe liver damage and even a condition requiring a liver transplant.
HIV testing reach is still limited. An estimated 40% of people with HIV (more than 14 million) remain undiagnosed and do not know their infection status.
![The Movius line separates regions of the world where Acheulean hand axes were made from regions wher](https://biology-forums.com/gallery/47/medium_275510_22_02_15_5_56_55_207692261.jpeg)
![Daniel Burnham’s Flatiron Building (1902) was one of the first to use steel girders to hold up the b](https://biology-forums.com/gallery/47/medium_6_24_08_15_12_36_54_224241797.jpeg)