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。
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."