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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 immune system needs 9.5 hours of sleep in total darkness to recharge completely.
To maintain good kidney function, you should drink at least 3 quarts of water daily. Water dilutes urine and helps prevent concentrations of salts and minerals that can lead to kidney stone formation. Chronic dehydration is a major contributor to the development of kidney stones.
Patients who cannot swallow may receive nutrition via a parenteral route—usually, a catheter is inserted through the chest into a large vein going into the heart.
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.