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.
Causes of a change in tongue texture. If your tongue appears to be furry or hairy, itâs most likely caused by a course of antibiotics. Radiation to the head or neck can also lead to this symptom. It can also develop if you consume too much of an irritating substance, such as coffee or mouthwash, or if you smoke.