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When blood is deoxygenated and flowing back to the heart through the veins, it is dark reddish-blue in color. Blood in the arteries that is oxygenated and flowing out to the body is bright red. Whereas arterial blood comes out in spurts, venous blood flows.
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.
The horizontal fraction bar was introduced by the Arabs.
Alzheimer's disease affects only about 10% of people older than 65 years of age. Most forms of decreased mental function and dementia are caused by disuse (letting the mind get lazy).
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.