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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.
Adult head lice are gray, about ? inch long, and often have a tiny dot on their backs. A female can lay between 50 and 150 eggs within the several weeks that she is alive. They feed on human blood.
The most dangerous mercury compound, dimethyl mercury, is so toxic that even a few microliters spilled on the skin can cause death. Mercury has been shown to accumulate in higher amounts in the following types of fish than other types: swordfish, shark, mackerel, tilefish, crab, and tuna.
The modern decimal position system was the invention of the Hindus (around 800 AD), involving the placing of numerals to indicate their value (units, tens, hundreds, and so on).
Always store hazardous household chemicals in their original containers out of reach of children. These include bleach, paint, strippers and products containing turpentine, garden chemicals, oven cleaners, fondue fuels, nail polish, and nail polish remover.