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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.
More than 2,500 barbiturates have been synthesized. At the height of their popularity, about 50 were marketed for human use.
There are approximately 3 million unintended pregnancies in the United States each year.
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.
Astigmatism is the most common vision problem. It may accompany nearsightedness or farsightedness. It is usually caused by an irregularly shaped cornea, but sometimes it is the result of an irregularly shaped lens. Either type can be corrected by eyeglasses, contact lenses, or refractive surgery.