Huangdi asked Qibo: When water and grain enter the mouth and are transported to the intestines and stomach, their fluids separate into five types. In cold weather with thin clothing, they become urine and qi. In hot weather with thick clothing, they become sweat. When sorrow and qi combine, they become tears. When there is internal heat and stomach prolapse, they become saliva. When pathogenic qi reverses internally, the qi becomes blocked and does not flow, leading to water swelling. I know this is the case, but I do not know how it arises. I wish to hear the explanation.
Qibo replied: Water and grain both enter the mouth, and their flavors are of five types, each flowing to its respective sea. The body fluids each follow their own pathways. Thus, the triple energizer emits qi to warm the muscles, fill the skin, and serve as its essence. What flows but does not move becomes fluid. In hot weather with thick clothing, the striae and interstices open, causing sweat to emerge. When cold lingers between the muscles, the accumulation of foam causes pain. In cold weather, the striae and interstices close, and the qi and dampness do not flow. Water flows downward to the bladder, becoming urine and qi. Among the five zang and six fu organs, the heart is the ruler, the ears listen, the eyes observe, the lungs assist, the liver commands, the spleen protects, and the kidneys govern the exterior. Thus, the body fluids of the five zang and six fu organs all seep upward to the eyes. When the heart is sorrowful and qi combines, the heart system becomes tense, causing the lungs to rise, and the fluids overflow upward. The heart system and lungs cannot fully rise, sometimes going up and sometimes down, hence coughing and tears emerge. Internal heat causes the stomach to consume grain excessively, and the digestion of grain causes worms to move up and down, filling the intestines and stomach, leading to stomach prolapse. Stomach prolapse causes qi to counterflow, hence saliva emerges.
The body fluids of the five grains, when harmonized and combined, form a paste that seeps inward into the bone cavities, nourishing the brain marrow, and flowing downward to the yin-yang. If yin-yang is not harmonious, it causes the fluids to overflow and flow downward to the yin, reducing the marrow and fluids, leading to deficiency. Deficiency causes pain in the lower back and legs. If the qi pathways of yin-yang are blocked, the four seas are obstructed, the triple energizer does not drain, and the body fluids do not transform, water and grain accumulate in the intestines and stomach, separate in the ileum, and remain in the lower jiao, unable to seep into the bladder, causing the lower jiao to swell. If water overflows, it leads to water swelling. This is the Nishun of the five separations of body fluids.