灵枢经·决气 Discourse on Distinguishing the Qi
黄帝曰：余闻人有精、气、津、液、血、脉，余意以为一气耳，今乃辨为六名，余不知其所以然。歧伯曰：两神相搏，合而成形，常先身生，是谓精。何谓气？歧伯曰：上焦开发，宣五谷味，熏肤、充身、泽毛，若雾露之溉，是谓气。何谓津？歧伯曰：腠理发泄，汗出溱溱，是谓津。何谓液？歧伯曰：谷入气满，淖泽注于骨，骨属屈伸，泄泽补益脑髓，皮肤润泽，是谓液。何谓血？歧伯曰：中焦受气，取汁变化而赤，是谓血。何谓脉？歧伯曰：壅遏营气，令无所避，是谓脉。
黄帝曰：六气有，有馀不足，气之多少，脑髓之虚实，血脉之清浊，何以知之？歧伯曰：精脱者，耳聋；气脱者，目不明；津脱者，腠理开，汗大泄；液脱者，骨属屈伸不利，色夭，脑髓消，胫痹，耳数鸣；血脱者，色白，夭然不泽，其脉空虚，此其候也。
黄帝曰：六气者，贵贱何如？歧伯曰：六气者，各有部主也，其贵贱善恶，可为常主，然五谷与胃为大海也。
Huangdi said: 'I have heard that the human being possesses essence, qi, fluid, humor, blood, and vessels. In my own thinking I had supposed these to be but a single qi; yet now they are distinguished into six separate names, and I do not understand the reason for this.' Qibo said: 'When the two spirits contend and unite to form the body, that which is always generated prior to the body itself is called essence. What is called qi?' Qibo said: 'When the upper burner opens and disperses, spreading abroad the flavors of the five grains, warming the skin, filling the body, and moistening the body hair — like the irrigation of mist and dew — this is called qi. What is called fluid?' Qibo said: 'When the interstices release and open, so that sweat pours out profusely, this is called jin — the thin, readily-flowing fluid that vents outward as sweat. What is called humor?' Qibo said: 'When grain enters and the qi becomes full, and a rich moistness pours into the bones, so that the joints can flex and extend, this moistness supplementing and benefiting the brain and marrow so that the skin becomes lustrous, this is called ye — the thicker, denser humor. What is called blood?' Qibo said: 'When the middle burner receives qi and, taking up the fluid, transforms it and turns it red, this is called blood. What is called the vessel?' Qibo said: 'That which contains and restrains the nutritive qi, so that it has nowhere to escape, this is called the vessel.'
Huangdi said: 'Among these six qi there is surplus and insufficiency, abundance and scarcity of qi, deficiency and excess of the brain and marrow, and clarity and turbidity of the blood vessels — how does one come to know these?' Qibo said: 'When essence is lost, there is deafness. When qi is lost, the eyes become dim. When fluid is lost, the interstices open and sweat pours out excessively. When humor is lost, the joints lose their ease of flexion and extension, the complexion becomes withered, the brain and marrow waste away, the lower legs become impeded, and the ears ring repeatedly. When blood is lost, the complexion turns pale, withered and without luster, and the pulse becomes hollow and empty — these are the signs of loss.'
Huangdi said: 'As for these six qi, which is more precious and which is less so?' Qibo said: 'Each of the six qi has its own region and governance, and their relative precedence, whether favorable or unfavorable, may each be taken as a constant standard; yet it is the five grains together with the stomach that serve as their great sea.'