Tongue manifestation changes in the development of diseases. In the exogenous dis'eases, the tongue fur changing from thin to thick means that the pathogen enters the interior. while the tongue fur changing from thick to thin indicates the withdrawal of pathogen and recovery of the healthy qi. The tongue fur changing from white to yellow indicates that the pathogenic factors turn to be heat ones; while the tongue fur changing from yellow to white signifies the relief of heat pathogen. In the development of diseases, the tongue turning into red and crimson means the heat enters deep; the tongue color lightening means the reduction of heat in stable phase. Also see Insufficiency of Healthy Qi.