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Vampire bats have a natural anticoagulant in their saliva that permits continuous bleeding after they painlessly open a wound with their incisors. This capillary blood does not cause any significant blood loss to their victims.
Interferon was scarce and expensive until 1980, when the interferon gene was inserted into bacteria using recombinant DNA technology, allowing for mass cultivation and purification from bacterial cultures.
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 Babylonians wrote numbers in a system that used 60 as the base value rather than the number 10. They did not have a symbol for "zero."
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.