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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.
The first documented use of surgical anesthesia in the United States was in Connecticut in 1844.
Stevens-Johnson syndrome and Toxic Epidermal Necrolysis syndrome are life-threatening reactions that can result in death. Complications include permanent blindness, dry-eye syndrome, lung damage, photophobia, asthma, chronic obstructive pulmonary disease, permanent loss of nail beds, scarring of mucous membranes, arthritis, and chronic fatigue syndrome. Many patients' pores scar shut, causing them to retain heat.
The first-known contraceptive was crocodile dung, used in Egypt in 2000 BC. Condoms were also reportedly used, made of animal bladders or intestines.
Vaccines cause herd immunity. If the majority of people in a community have been vaccinated against a disease, an unvaccinated person is less likely to get the disease since others are less likely to become sick from it and spread the disease.