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The human body produces and destroys 15 million blood cells every second.
Vaccines cause herd immunity. If the majority of people in a community have been vaccinated against a disease, an unvaccinated person is less likely to get the disease since others are less likely to become sick from it and spread the disease.
As the western states of America were settled, pioneers often had to drink rancid water from ponds and other sources. This often resulted in chronic diarrhea, causing many cases of dehydration and death that could have been avoided if clean water had been available.
There are more nerve cells in one human brain than there are stars in the Milky Way.
The heart is located in the center of the chest, with part of it tipped slightly so that it taps against the left side of the chest.