20. If the patient frequently desires to rinse their mouth but does not wish to swallow, and the stool is black yet easy to pass, this indicates the presence of blood stasis (Blood Stasis). It should be treated with Xijiao Dihuang Tang (Rhinoceros Horn and Rehmannia Decoction).
When the pathogen resides in the Blood aspect, there is no desire for drinking water. However, due to heat pathogens consuming body fluids causing dryness of the mouth, there is a desire to seek relief from water; thus, one only wishes to rinse the mouth without swallowing. When blood stasis overflows into the intestines, the color of the blood turns black after long-term stagnation. Since blood nature is soft and moist, the stool becomes black but passes easily. Rhinoceros horn (Xijiao) has a salty taste and enters the Lower Jiao Blood aspect to clear heat; Rehmannia root (Dihuang) eliminates accumulations and nourishes Yin; White Peony root (Baishao) removes bad blood and generates new blood; Moutan bark (Danpi) drains latent fire within the blood. Thus, the accumulated blood naturally flows downward, so this mild formula is used to regulate it.
Formula of Xijiao Dihuang Tang (Following the method of Sweet, Salty, and Slightly Bitter)
Prepared Rehmannia Root (Gan Dihuang) [Rehmanniae Radix Preparata] (1 liang)
Raw White Peony Root (Sheng Baishao) [Paeoniae Radix Alba] (3 qian)
Moutan Bark (Danpi) [Moutan Cortex] (3 qian)
Rhinoceros Horn (Xijiao) [Rhinocerotis Cornu] (3 qian)
Boil five cups of water until two cups remain. Divide into two doses for administration. Boil the dregs again to obtain one cup for administration.