What disease is black tongue coating?

Tongue diagnosis is an important part of traditional Chinese medicine diagnosis. Tongue is an exposed internal organ. Tongue coating is produced by stomach qi. By looking at tongue, cold and heat, deficiency and excess, interior and exterior of diseases can be distinguished, and the severity, depth, change of body fluid, ups and downs of stomach qi, etc. of diseases can be inferred. Tongue coating is black, which is mostly transformed from gray coating or yellow coating, often due to a long time of illness or a serious stage of illness. Black main disease also has cold and heat points, if black and dry crack, even raw awn thorn, more common in heat extreme Jin dry syndrome; black and smooth, and accompanied by light tongue quality, more common yang deficiency yin cold extreme danger. Black fur should also be ruled out caused by moss, if dyed fur, do not panic.