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 coated tongue vary. The difference in the tongue coating appearance can help narrow down the causes and treatments. White Tongue The tongue appears to have a thick, white coating due to inflammation and trapped particles, such as dead cells and bacteria. The causes of a white tongue coating are varied. Usually, white tongue poses little concern and may be caused by dehydration, mouth breathing, medications, alcohol use, smoking, or fever.