The Four Stages or Four Levels are from the book ''Discussion of Warm Diseases'' by Ye Tian Shi, written in the years 1667-1746.
The stages are in order from surface to deep internal and from "light" sickness to death:
*Wei level treated by releasing the exterior
*Qi level treated by dispelling heat and promoting body fluids
Stomach and Spleen damp heat
*Ying level treated by cooling fire and tonifing the yin
Heat in Nutritive qi portion
Heat in Pericardium
*Blood level treated by tonifing the yin and qi and stopping bleeding.
Heat Victorious moves blood
Heat victorious stirs wind
Empty wind agitates in the interior
Collapse of yin
Collapse of yang
Separation of yin and yang