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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.
Most childhood vaccines are 90–99% effective in preventing disease. Side effects are rarely serious.
When blood is exposed to air, it clots. Heparin allows the blood to come in direct contact with air without clotting.
About 3% of all pregnant women will give birth to twins, which is an increase in rate of nearly 60% since the early 1980s.
Cocaine was isolated in 1860 and first used as a local anesthetic in 1884. Its first clinical use was by Sigmund Freud to wean a patient from morphine addiction. The fictional character Sherlock Holmes was supposed to be addicted to cocaine by injection.