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When blood is exposed to air, it clots. Heparin allows the blood to come in direct contact with air without clotting.
Most childhood vaccines are 90–99% effective in preventing disease. Side effects are rarely serious.
People with alcoholism are at a much greater risk of malnutrition than are other people and usually exhibit low levels of most vitamins (especially folic acid). This is because alcohol often takes the place of 50% of their daily intake of calories, with little nutritional value contained in it.
The first-known contraceptive was crocodile dung, used in Egypt in 2000 BC. Condoms were also reportedly used, made of animal bladders or intestines.
In the United States, an estimated 50 million unnecessary antibiotics are prescribed for viral respiratory infections.