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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.
Addicts to opiates often avoid treatment because they are afraid of withdrawal. Though unpleasant, with proper management, withdrawal is rarely fatal and passes relatively quickly.
Most childhood vaccines are 90–99% effective in preventing disease. Side effects are rarely serious.
The first documented use of surgical anesthesia in the United States was in Connecticut in 1844.
Autoimmune diseases occur when the immune system destroys its own healthy tissues. When this occurs, white blood cells cannot distinguish between pathogens and normal cells.