BNYS notes

Most important line to be noted for tongue diagnosis

a dry tongue with a bitter taste in the mouth is symptomatic of Heart fire.

dry tongue with chest and hpochondriac pain is caused by stagnation of liver qi from emotional problems;

a dry tongue with dry throat is due to an irregular diet and overwork

An example from Chao's book is illustrative: "During pregnancy When the fetus is restless. . . and the mother presents with a red face and a blue tongue, the child will die and the mother will live; if the mother's face is blue and her tongue is red and she drools, she will die and the child will live."