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Most childhood vaccines are 90–99% effective in preventing disease. Side effects are rarely serious.
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.
Blood in the urine can be a sign of a kidney stone, glomerulonephritis, or other kidney problems.
The first-known contraceptive was crocodile dung, used in Egypt in 2000 BC. Condoms were also reportedly used, made of animal bladders or intestines.
The term bacteria was devised in the 19th century by German biologist Ferdinand Cohn. He based it on the Greek word "bakterion" meaning a small rod or staff. Cohn is considered to be the father of modern bacteriology.