Unlike the equator and the Tropic of Cancer and the Tropic of Capricorn, the Prime Meridian and all lines of longitude are completely imaginary lines and have no significance with regard to the Earth or to its relationship with the sun.
Black hairy tongue typically results when projections on the tongue called papillae grow longer and don't shed like normal. This makes the tongue look hairy. Debris, bacteria or other organisms can collect on the papillae and result in discoloration. The cause of black hairy tongue can't always be determined.
Hairy Tongue: Abnormal sensation where the tongue feels hairy or furry. See detailed information below for a list of 9 causes of Hairy Tongue, Symptom Checker, including diseases and drug side effect causes. Â» Review Causes of Hairy Tongue: Causes | Symptom Checker Â».