The syndromes of the yin (nutrient) stage occur when pathogenic mild heat is transmitted into the superficial layer of the blood. Ying is a component of the blood, so the disease location is actually in the heart and pericardium. Pathological characteristics show the injury of nutrient yin and the disturbance of heart-mind.

Pathogenic heat injuring nutrient yin
Fever (worse at night), irritability, insomnia, or even coma and delirium, recessive rashes, slight thirst, deep red tongue proper, thready and rapid pulse.
Pathogenic mild heat invades deeply into the ying stage, thus scorching and injuring the nutrient yin and leading to insufficiency of blood, so the fever worsens at night and a rapid thready pulse results. pathogenic heat steams nutrient yin causing a slight thirst. Heat disturbs the mind leading to irritability, insomnia, or even coma and delirium. Pathogenic heat causes a disorderly flow of blood, thus a recessive, deep red tongue proper manifests.

Heat attacking the pericardium
Fever, coma, delirium, deep red tongue proper, rapid pulse. After pathogenic heat attacks the pericardium, it disturbs the heart-mind bringing on fever, coma, and delirium. A deep red tongue proper is a sign of heat in the blood. Rapid pulse indicates excessive heat.