Woodblock illustration of 'White-coated tongue' (
baitai she) from
Yuan Ao Shi shanghan jinjinglu (Mr Yuan Ao's Golden Mirror of Cold Damage), a treatise on tongue diagnosis -- original text by Ao Jiweng (Song period, 960-1279); additional material by Du Ben (Tao Hua) (Yuan period, 1206-1368 ); continuation by Xue Ji and Ma Chongru (Ming period 1368-1644). This edition was published in 529 (8th year of the Jiajing reign period of the Ming dynasty).
The text states: In White-coated tongue image, the tongue is pale red around the edges and has a slimy white coating in the middle. This tongue image shows that malign Qi has entered the body. It is a sign of heat in the Cinnabar Field (dantian) and cold in the chest, and is classified as a semi semi-superficial, semi-internal (shaoyang) symptom. Suitable treatments are Minor Bupleurum Decoction (xiao chaihu tang) and Cape Jasmine Bean Decoction (zhizi dou tang).