阴生于上，胃以纯阳而含阴气，有阴则降，浊气下降，是以清虚而善容纳。阳生于下，脾以纯阴而
含阳气，有阳则升，清阳上升，是以温暖而善消磨。水谷入胃，脾阳磨化，渣滓下传而为粪溺，精华上
奉而变气血。气统于肺，血藏于肝，肝血温升则化阳神，肺气清降则产阴精。五脏皆有精，悉受之于肾。
五脏皆有神。悉受之于心。五脏皆有血，悉受之于肝。五脏皆有气，悉受之于肺。总由土气之所化生也。
土爰稼穑，稼穑作甘，谷味之甘者，秉土气也。五谷香甘以养脾胃，土气充盈，分输四子，己土左旋，谷
气归于心肺；戊土右转，谷精归于肾肝；脾胃者仓廪之官，水谷之海，人有胃气则生，绝胃气则死，
胃气即水谷所化，食为民天，所关非细也。
水谷入胃，消于脾阳。水之消化，较难于谷，缘脾土磨化，全赖于火，火为土母，火旺土燥，力
能克水，脾阳蒸动，水谷精华化为雾气，游溢而上，归于肺家，肺金清肃，雾气降洒，化而为水，如釜
水沸腾，气蒸为雾也。气化之水，有精有粗，精者入于脏腑而为津液，粗者入于膀胱而为溲溺，溲溺通利，
胃无停水，糟粕后传，是以便干。《灵枢·营卫生会》∶上焦如雾，中焦如沤，下焦如渎。气水变化于
中焦，沤者气水方化而未盛也。及其已化，则气腾而上，盛于胸膈，故如雾露。水流而下，盛于膀胱，
故如川渎。川读之决，由于三焦。《素问·灵兰秘典》∶三焦者决渎之官，水道出焉。盖三焦之火秘，则
上温脾胃而水道通，三焦之火泄，则下陷膀胱而水窍闭。《灵枢·本输》∶三焦者足太阳、少阴之所将，
太阳之别也，上踝五寸，别入贯 肠，出于委阳，并太阳之正，入络膀胱，约下焦，实则闭癃，虚则遗溺，
以水性蛰藏，太阳寒水蛰藏，三焦之火，秘于肾脏，则内温而外清。水府清通，上窍常开，是以气化之水
，渗于膀胱，而小便利。若太阳寒水不能蛰藏，三焦之火泄于膀胱，膀胱热癃，
水窍不开。脾胃寒郁，但能消谷，不能消水，水不化气上腾，爰与谷滓并入二肠而为泄利。泄利之家，水
入二肠，而不入膀胱，是以小便不利，所谓实则闭癃者，三焦之火泄于膀胱也。
阴气产生于上部，胃虽然属于纯阳之腑但内含阴气，因为有阴气所以能下降，浊气随之下降，因此胃保持清虚状态而善于容纳食物。阳气产生于下部，脾虽然属于纯阴之脏但内含阳气，因为有阳气所以能上升，清阳之气随之上升，因此脾保持温暖状态而善于消化腐熟水谷。
水谷进入胃中，由脾阳进行磨碎和化生，残渣下传形成粪便和小便，精华上输并转化为气血。气由肺所统摄，血由肝所贮藏，肝血温煦上升则化为阳神，肺气清肃下降则产生阴精。五脏都藏有精，这些精全部来源于肾；五脏都藏有神，这些神全部来源于心；五脏都藏有血，这些血全部来源于肝；五脏都藏有气，这些气全部来源于肺。这一切总归是由脾胃土气的化生作用而来。
土具有种植和收获的特性，种植和收获产生甘味，谷物味甘是因为禀受了土气。五谷的香甘之味用来滋养脾胃，土气充盈后，分流输布给其他四脏：己土（脾）向左旋转，谷气归于心和肺；戊土（胃）向右旋转，谷精归于肾和肝。脾胃是负责储藏饮食的官职，是水谷汇聚的大海，人只要有胃气就能生存，失去胃气就会死亡，胃气就是由水谷化生而来的，饮食对百姓来说如同天一样重要，其关系非同小可。
水谷进入胃中，在脾阳的作用下被消化。水的消化比谷物更难，因为脾土的磨化作用完全依赖于火，火是土的母亲，火旺则土燥，力量能够克制水，脾阳蒸腾运动，将水谷的精华化为雾气，游溢向上，归属于肺，肺金清肃，雾气降洒下来，又化为水，就像锅里的水沸腾，蒸汽变成雾气一样。气化而成的水，有精细和粗糙之分，精细的进入脏腑成为津液，粗糙的进入膀胱成为小便，小便通利，胃中没有停滞的水，糟粕向后传导，因此大便干燥。《灵枢·营卫生会》说：上焦像雾露弥漫，中焦像沤泡发酵，下焦像沟渠流通。气和水在中焦发生变化，“沤”是指气和水分化但尚未旺盛的状态。等到已经化生之后，气就升腾而上，充满胸膈，所以像雾露；水流向下，充满膀胱，所以像河流沟渠。沟渠的疏通，取决于三焦。《素问·灵兰秘典论》说：三焦是疏通水道的官职，水道由此而出。大概三焦之火秘藏，则上温脾胃而水道通畅；三焦之火外泄，则下陷膀胱而水窍闭塞。《灵枢·本输》说：三焦是足太阳膀胱经和足少阴肾经所统领的，是太阳经的别络，在外踝上五寸处，别行深入贯穿大肠，出于委阳穴，与太阳经的正脉并行，入络于膀胱，约束下焦，实证表现为小便闭阻不通，虚证表现为遗尿，这是因为水性主蛰伏收藏，太阳寒水主蛰伏收藏，三焦之火秘藏于肾脏，则体内温暖而体表清静。水府清通，上窍常开，因此气化之水渗入膀胱，小便就通利。如果太阳寒水不能蛰伏收藏，三焦之火泄于膀胱，导致膀胱热结小便不通，水窍不开。脾胃寒郁，只能消化谷物，不能消化水湿，水不能化为气上升，于是与谷渣一起并入大小肠而导致泄泻痢疾。患有泄泻的人，水进入大小肠而不进入膀胱，因此小便不利，这就是所谓的“实证表现为小便闭阻不通”，指的是三焦之火泄于膀胱所致。
Yin arises from the upper part; the Stomach, although a pure Yang organ, contains Yin Qi. Because it possesses Yin, it descends; turbid Qi descends with it, thus keeping the Stomach clear and empty, enabling it to receive and hold food well. Yang arises from the lower part; the Spleen, although a pure Yin organ, contains Yang Qi. Because it possesses Yang, it ascends; clear Yang Qi ascends with it, thus keeping the Spleen warm, enabling it to digest and transform food well.
When water and grain enter the Stomach, Spleen Yang grinds and transforms them. The dregs are transmitted downward to become feces and urine, while the essence is sent upward to transform into Qi and Blood. Qi is governed by the Lung, and Blood is stored in the Liver. When Liver Blood warms and ascends, it transforms into Yang Shen (Spirit); when Lung Qi clears and descends, it produces Yin Jing (Essence). All five Zang organs possess Jing (Essence), which is entirely received from the Kidney. All five Zang organs possess Shen (Spirit), which is entirely received from the Heart. All five Zang organs possess Blood, which is entirely received from the Liver. All five Zang organs possess Qi, which is entirely received from the Lung. All of this ultimately stems from the transformation and generation by the Earth Qi (Spleen/Stomach).
Earth has the nature of sowing and reaping; sowing and reaping produce the Sweet flavor. Grains taste sweet because they embody Earth Qi. The fragrant and sweet flavors of the five grains nourish the Spleen and Stomach. When Earth Qi is abundant, it distributes to the other four Zang organs: Ji Earth (Spleen) rotates leftward, sending Grain Qi to the Heart and Lung; Wu Earth (Stomach) rotates rightward, sending Grain Essence to the Kidney and Liver. The Spleen and Stomach are the officials responsible for storage and granaries, the sea of water and grain. If a person has Stomach Qi, they live; if Stomach Qi is absent, they die. Stomach Qi is transformed from water and grain. Food is the heaven for the people, and its importance is not slight.
Water and grain enter the Stomach and are digested by Spleen Yang. The digestion of water is more difficult than that of grain, because the grinding and transforming action of Spleen Earth relies entirely on Fire. Fire is the mother of Earth; when Fire is vigorous, Earth becomes dry, possessing the power to overcome Water. Spleen Yang steams and moves, transforming the essence of water and grain into mist. This mist floats upward and returns to the Lung. Lung Metal clears and descends, sprinkling the mist down, which transforms back into water. This is like water boiling in a pot, where steam rises as mist. The water resulting from Qi transformation has fine and coarse parts. The fine part enters the Zang and Fu organs to become Jin Ye (Body Fluids); the coarse part enters the Bladder to become Xiao Niao (Urine). When Xiao Niao flows freely, there is no stagnant water in the Stomach, waste materials are transmitted posteriorly, and thus stool becomes dry. *Ling Shu: Ying Wei Sheng Hui* states: "The Upper Jiao is like mist; the Middle Jiao is like a fermenting vat; the Lower Jiao is like a ditch." Qi and water change in the Middle Jiao. "Ao" (fermenting vat) refers to the state where Qi and water are just beginning to transform but are not yet vigorous. Once transformation is complete, Qi rises and fills the chest and diaphragm, hence resembling mist and dew. Water flows downward and fills the Bladder, hence resembling rivers and ditches. The dredging of these ditches depends on the San Jiao (Triple Burner). *Su Wen: Ling Lan Mi Dian Lun* states: "The San Jiao is the official who dredges the waters; the water passages emerge from it." Generally, if the Fire of the San Jiao is sealed, it warms the Spleen and Stomach above and ensures smooth water passages; if the Fire of the San Jiao leaks, it sinks into the Bladder below and closes the water orifices. *Ling Shu: Ben Shu* states: "The San Jiao is commanded by the Foot-Taiyang and Foot-Shaoyin meridians; it is a branch of the Taiyang meridian. At five cun above the malleolus, it branches off, penetrates through the intestines, emerges at Weiyang (BL39), runs parallel with the main channel of Taiyang, enters and connects with the Bladder, and regulates the Lower Jiao. In excess conditions, it causes Bi Long (dysuria/retention); in deficiency conditions, it causes Yi Niao (incontinence)." This is because Water nature is to hibernate and store. Foot-Taiyang Cold Water hibernates and stores; the Fire of the San Jiao is sealed within the Kidney, warming internally and clearing externally. When the Water Mansion is clear and unobstructed, the upper orifices remain open. Thus, water transformed by Qi seeps into the Bladder, and urination is smooth. If Foot-Taiyang Cold Water cannot hibernate and store, and the Fire of the San Jiao leaks into the Bladder, the Bladder suffers from Heat and Bi Long, and the water orifice does not open. If the Spleen and Stomach are cold and depressed, they can only digest grain but not water. Water fails to transform into Qi and ascend, so it mixes with grain dregs and enters the two intestines, causing Xie Li (diarrhea/dysentery). In cases of diarrhea, water enters the two intestines instead of the Bladder, leading to difficult urination. This is what is meant by "excess conditions cause Bi Long," referring to the leakage of San Jiao Fire into the Bladder.