(4)        The Black coating:  this is usually developed from deep yellow or gray coating.  Whether it is syndrome for heat or cold, black coating generally indicates serious illness.  The darker the blackness, the more serious is the condition.  If black coating comes with fissure and spiky tongue, it indicates extreme heatiness and dryness; if black and dry fur is seen at the center of the tongue, the patient usually has a dry intestine and is also constipated, or that the stomach is failing in its function; if the position of the black fur is at the root portion of the tongue, then the lower Jiau is extremely heaty; if the black fur is at the top of the tongue, then the heart fire is hyperactive.  Black but watery and moist fur, but accompanied by pale tongue, means that extreme internal Yin cold is stagnating dampness; black but sticky fur indicates internal blockage due to dampness and phlegm.