或问余曰。灵枢经曰。水谷者。常并居胃中。成糟粕。而俱下于大肠。而成下焦。渗而俱下
。济泌别汁。循下焦。而渗入膀胱焉。王冰曰。水液自回肠泌别汁。渗入膀胱之中胞。气化
之而为溺。以泄出也。杨介云。水谷自小肠盛受于阑门。以分别也。其水。则渗灌入于膀胱
上口。而为溲便。详以上三说。则小便即泌别之水液。渗入膀胱以出者也。素问则曰。饮入
于胃。游溢精气。上输于脾。脾气散精。上归于肺。通调水道。下输膀胱。则小便又似水饮
精
微之气。上升脾肺。运化而后成者也。彼此不同。将何所凭乎。余曰。凭夫理耳。且夫溲溺
者。果何物耶。水而已矣。水之下流。其性则然也。故饮入于胃。其精气虽不上升。其饮之
本
。固不能上升。体也。既不能上升。则岂可谓小便。独为气化所成者哉。惟其不能上升者。
必有待于能上升者。为之先导。故素问又曰。膀胱者。津液藏焉。气化则能出矣。且水者。
气之子。气者。水之母。气行则水行。气滞则水滞。或者又谓。小便纯由泌别。不由运化。
盖不明此理故也。虽然。膀胱。固曰津液之府。至于受盛津液。则又有胞。而居膀胱之中焉。
故素问曰。胞移热于膀胱。灵枢经曰。膀胱之胞薄以濡。类纂曰。膀胱者。胞之室。且夫
胞之居于膀胱也。有上口而无下口。津液既盛于胞。无由自出。必因乎气化。而后能渐浸润
于胞外。积于胞下之空处。遂为溺以出于前阴也。素问所谓膀胱津液藏焉者。盖举膀胱以该
胞也。若曰胞下无空处。则人溺急时至厕。安能即出乎。夫惟积满胞下空处。而不可再容。
故急。急则至厕即出矣。或言胞有下口。而无上口。或言胞上下皆有口。或言胞有小窍而为
注泄之路。不亦妄欤。
有人问我：“《灵枢经》说：‘饮食水谷，常常共同居住在胃中，消化成为糟粕，然后一起下行进入大肠，形成下焦的功能。通过过滤分离，汁液向下渗透，沿着下焦渗入膀胱。’王冰注释说：‘水液从回肠分泌出汁液，渗入膀胱中的胞（指膀胱内部结构或尿囊），经过气化作用变成尿液，从而排泄出来。’杨介说：‘水谷从小肠在阑门处接受并分别处理。其中的水分，则渗透灌入膀胱上口，形成小便和大便。’详细考察以上三种说法，那么小便就是经过泌别的水液，渗入膀胱后排出体外的。然而《素问》却说：‘饮水进入胃中，游溢精气，向上输送到脾；脾气散布精微，向上归于肺；肺通调水道，向下输送到膀胱。’这样看来，小便似乎又是水饮的精微之气，上升到脾和肺，经过运化之后才形成的。这两种说法彼此不同，该依据哪一种呢？”
我说：“依据的是道理罢了。况且，小便到底是什么东西呢？不过是水而已。水往低处流，这是它的本性。所以，饮水进入胃中，虽然其精气不一定都上升，但作为水的本体，本来就不能上升。既然不能上升，怎么能说小便仅仅是由气化作用形成的呢？正因为那些不能上升的东西，必定需要依靠能上升的东西作为先导。所以《素问》又说：‘膀胱是津液藏聚的地方，经过气化作用才能排出。’而且，水是气的儿子，气是水的母亲。气运行则水运行，气停滞则水停滞。有的人又说，小便纯粹是由泌别作用形成的，与运化无关，这大概是不明白这个道理的缘故吧。
虽然如此，膀胱确实被称为津液之府。至于承受和盛纳津液，还有胞存在，它位于膀胱之中。所以《素问》说：‘胞的热邪转移给膀胱。’《灵枢经》说：‘膀胱的胞壁薄而湿润。’《类纂》说：‘膀胱是胞的居室。’况且，胞位于膀胱内，只有上口而没有下口。津液既已充满在胞中，没有途径自行排出，必须依赖气化作用，然后才能逐渐浸润到胞外，积聚在胞下方的空处，最终变成尿液从前阴排出。《素问》所说的‘膀胱津液藏焉’，其实是举膀胱之名来概括包括胞在内的整体情况。如果说胞下方没有空处，那么当人尿急时去厕所，怎么能立刻排出来呢？正是因为积聚满了胞下方的空处，再也容纳不下，所以才感到急迫，一急迫就去厕所立即排出了。有人说胞有下口而无上口，有人说胞上下都有口，有人说胞有小孔作为注泄的路径，这些说法不都是荒谬的吗？”
Someone asked me, "The *Ling Shu* (Spiritual Pivot) states: 'Food and drink often reside together in the stomach. They transform into dregs and descend together to the large intestine, forming the Lower Jiao (Lower Burner). Through filtration and separation, the fluids seep downward along the Lower Jiao and penetrate into the bladder.' Wang Bing commented: 'Body fluids separate from the ileum as distinct juices, penetrating into the bladder's *bao* (bladder sac/internal structure). Through Qi transformation (Qi Hua), they become urine for excretion.' Yang Jie stated: 'Food and drink are received and separated at the Lanmen (Gate of Separation) in the small intestine. The water component penetrates and irrigates into the upper orifice of the bladder, forming urine and feces.' Examining these three explanations, it appears that urine is simply the fluid separated by filtration, which penetrates the bladder and is excreted. However, the *Su Wen* (Basic Questions) says: 'When drink enters the stomach, its essence and qi float freely and are transported upward to the Spleen. The Spleen scatters the essence, sending it upward to return to the Lung. The Lung regulates the water passages, transporting them downward to the bladder.' In this case, urine seems to be formed from the essence and qi of ingested fluids, which rise to the Spleen and Lung, undergo transformation, and then become urine. These two accounts differ. Which one should we rely on?"
I replied, "We rely on principle. Moreover, what exactly is urine? It is merely water. Water flows downward; this is its nature. Therefore, when drink enters the stomach, although its essence and qi may not necessarily ascend, the substance of the water itself cannot ascend. Since it cannot ascend, how can we claim that urine is formed solely by Qi transformation? Precisely because those things that cannot ascend must rely on those that can ascend as a precursor. Thus, the *Su Wen* also states: 'The Bladder is the storehouse of body fluids; through Qi transformation, they are able to exit.' Furthermore, water is the child of Qi, and Qi is the mother of water. When Qi moves, water moves; when Qi stagnates, water stagnates. Some argue that urine is purely the result of filtration/separation and has nothing to do with transformation/distribution. This is likely due to a failure to understand this principle.
Although so, the Bladder is indeed called the mansion of body fluids. Regarding the reception and storage of body fluids, there is the *bao* (sac/bladder interior), which resides within the Bladder. Hence, the *Su Wen* says: 'Heat from the Bao transfers to the Bladder.' The *Ling Shu* states: 'The Bao of the Bladder is thin and moist.' The *Lei Zuan* states: 'The Bladder is the chamber of the Bao.' Moreover, the Bao resides within the Bladder, having an upper orifice but no lower orifice. Once body fluids fill the Bao, there is no way for them to exit spontaneously. They must depend on Qi transformation to gradually infiltrate outside the Bao, accumulating in the empty space below the Bao, eventually becoming urine and exiting through the anterior yin. When the *Su Wen* says 'The Bladder stores body fluids,' it refers to the Bladder broadly to include the Bao. If there were no empty space below the Bao, how could one urinate immediately upon rushing to the toilet when urgent? It is precisely because the empty space below the Bao becomes full and cannot hold more that urgency arises; when urgent, one goes to the toilet and urinates immediately. Those who say the Bao has a lower orifice but no upper orifice, or that it has orifices both above and below, or that it has small apertures serving as channels for discharge, are all making absurd claims."