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(Miao Zhichun and Ke Yunbo both held this view, but their exposition was neither exhaustive nor precise. I now elaborate on it as follows.)

Yin (Fluid retention) is water; it is clear and non-viscous, representing a state where fluids are transforming into sweat or urine but have not yet fully formed. Tan (Phlegm) is thick and extremely viscous, representing a state where fluids are transforming into body fluids or blood but have not yet fully formed.

The generation of Yin arises from the failure of Qi transformation in the Sanjiao (Triple Burner); the failure of Sanjiao function stems from insufficient Mingmen Fire (Fire of the Gate of Life). The Classics state: "The Sanjiao is the official of irrigation, through which water passages flow." "The Bladder is the official of the capital, storing body fluids; only through Qi transformation can they be excreted." Generally, when water enters the Stomach, the Spleen disperses its essence, sending it upward to the Lung; this is Jin (Thin Fluids). The dregs pour into the Sanjiao, where they are steamed and moved by heat qi. Thus, without waiting to transform into urine, they may escape outward as sweat; hence, excessive sweating leads to reduced urination. Flowing downward into the Bladder, which has an upper opening but no lower opening, the fluids still rely on the Qi transformation of the Sanjiao to exit downward, hence it is said that "only through Qi transformation can they be excreted." Within the Sanjiao, it is called Water; within the Bladder, it is called Body Fluids. When Water is in the Sanjiao, its quality is clear and taste bland. When escaping outward as sweat, it becomes salty; when draining downward as urine, it becomes ammoniacal. All these changes result from the influence of human Qi, losing their original clear and bland nature. Therefore, both sweat and urine can be termed Body Fluids, but essentially they are all Water. If Fire power fails to transport, Water stagnates in the Middle Jiao and shoots upward to the Lung. The treatment method involves tonifying Fire and regulating Qi, which treats the root; inducing sweating and promoting urination treats the branch.

Tan (Phlegm), whether Dry Phlegm or Damp Phlegm, always results from Spleen Qi deficiency failing to perform healthy transportation. The essence of food and grain is transformed by Spleen Qi, reaching the muscles to become Blood, moistening dryness; reaching the sinews and bones to become Ye (Thick Fluids), facilitating flexion and extension. Now, with Spleen Qi deficiency, Earth fails to generate Metal, leading to weakness in the Danzhong (Sea of Qi). Consequently, force cannot reach the muscles, stagnating in the intestines and stomach, accumulating to form Phlegm; what has already reached the fascia may fail to transport to the sinews and bones, resulting in Phlegm hidden within the skin and fascia. Moreover, those with abundant Phlegm often have deficient Blood, causing occasional difficulty in joint movement; this is the reason. The treatment method involves strengthening the Spleen while simultaneously regulating the Sanjiao to assist the ascending, descending, transporting, and transforming functions of Qi, which treats the root; ventilating depression and breaking stasis treats the branch. For Dry Phlegm, clearing heat and generating fluids is added so that Phlegm has a carrier for expulsion. The reason for using methods to break stasis is that Phlegm belongs to the category of Blood, and retained Phlegm is treated similarly to Blood Stasis. Treating Phlegm must not involve tonifying Fire, nor should it involve promoting urination; adding Water and reducing Fire causes even Damp Phlegm to become more sticky and proliferative due to heat-fire stagnation, making it impossible to eradicate. This is the major principle of differentiating the treatment of Phlegm and Fluid Retention. As for patients suffering from Fluid Retention, they invariably have accompanying Phlegm; patients suffering from Phlegm may also have Fluid Retention. These two conditions often overlap, which is why ancient treatments did not distinguish them strictly. One must understand that diseases have distinct origins and symptoms have varying emphases. In cases of Fluid Retention accompanied by Phlegm, treating the Fluid Retention causes the Phlegm to dissipate spontaneously; if Phlegm is severe, Phlegm-treating methods can be combined. In cases where Fluid Retention arises from Phlegm, treating the Phlegm causes the Fluid Retention to resolve spontaneously; if Fluid Retention is severe, Fluid Retention-treating methods can be combined.