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Ying Qi (Nutritive Qi), also known as Ying Blood, cannot circulate on its own but relies on the propulsion of Qi, specifically directed by Zong Qi (Pectoral Qi). Therefore, it is called Ying Qi. This Qi is generated from dietary intake and Earthly Qi, representing the refined essence of food and fluids. Thus, the *Nei Jing* states: "When food and water enter the stomach, the clear portion becomes Ying Blood." It further states: "When food and water enter the stomach, their essence overflows and is transported upward to the Spleen. The Spleen distributes the fluid essences for the Stomach, transforming them into blood to nourish the body." It also says: "Ying Qi originates from the Middle Jiao (Middle Burner)." The Middle Jiao is the site where food and water are rotted and digested. Blood generation in the Middle Jiao follows two pathways: one flows from the right abdomen into the Chong Mai (Penetrating Vessel), known as the Sea of Blood; this blood remains static and constitutes Tian Gui (Heavenly Water/Reproductive Essence). The other flows from the left abdomen below the breast, following Zong Qi through the twenty-eight meridians as Ying Blood; this portion is dynamic and ceaseless. Regarding the circulation of Ying Blood, the Three Yin Meridians of the Hand travel from the chest to the hand, the Three Yang Meridians of the Hand from the hand to the head, the Three Yang Meridians of the Foot from the head to the foot, and the Three Yin Meridians of the Foot from the foot to the abdomen. Circulation proceeds first through the twelve meridians on the left, then those on the right. Since their circulation interconnects left and right, any disease affecting the Ying level on the left must inevitably affect the right, and vice versa.

Wei Qi (Defensive Qi) is also called Ren Qi (Human Qi) because it governs bodily movements and serves as the master of perception and motion. It is also called Yang Qi because it warms and nourishes the entire body. When condensed, it forms Wei Yang (Defensive Yang), which is the master receiving destiny and sustaining life. It is generated by combining Heavenly Qi (from respiration) and Earthly Qi (from diet). Heavenly Qi is formless and supremely firm, characteristics shared by Wei Qi. The *Nei Jing* states: "When food enters the stomach, the turbid portion becomes Wei Qi." The term "turbid" here refers to its fierce and rapid nature (Han). Due to this fierceness, it cannot circulate within the vessels but must move outside them, distinguishing Wei Yang from Ying Yin.

Wei Qi has a substance (Ti) and a function (Yong). The substance refers to the root of Wei Qi, which lies in the Kidney. The *Nei Jing* states that Wei Qi originates from the Lower Jiao (Lower Burner), typically starting from the Foot Shaoyin Kidney Meridian. However, it must attach to something to remain stationary; the Lower Jiao is rich in adipose tissue, and Wei Yang attaches to this fat, hence the statement that Wei Qi originates from the Lower Jiao. Like a lamp attached to oil, it burns continuously. Thus, later scholars referred to it as "Fire within Water." Not only humans, but all living things possess Yang Qi attached to their fats. The function refers to the branches of Wei Qi, with various meanings detailed below.

First, when Wei Qi circulates intermittently among the Five Zang Organs, the Five Shen (Spiritual Aspects) are generated. Combining with Zong Qi from the Upper Jiao after originating in the Lower Jiao, it corresponds to the Heart, generating Shen (Spirit) manifested as joy and laughter; it corresponds to the Lung... [text implies correspondence to other organs generating respective spirits]. Collectively, this is termed "Hui" (Wisdom/Clarity).

Second, when Wei Qi circulates intermittently among the Six Fu Organs, food and water are transformed. Rising from the Lower Jiao to combine with Zong Qi, it corresponds to the Stomach to govern reception, to the Gallbladder to govern decision-making, to the Small Intestine to govern digestion, to the Large Intestine to convey waste, and to the Bladder to govern seepage and diuresis. Collectively named San Jiao (Triple Burner), it facilitates the movement of fluids. The opening and closing of urination and defecation are controlled by the Wei Qi of the San Jiao, referred to as Yuan Qi (Source Qi) in the *Nan Jing*.

Third, the entry and exit of Wei Qi into the meridians distinguishes wakefulness from sleep. Upon exiting, it travels from the Kidney through the Shaoyin division (the gateway for Wei Qi entry/exit), ascending to the head where the five sense organs are utilized (as all Yang meridians ascend to the head); it utilizes the hands when traveling through Hand meridians, the feet through Foot meridians, generates wisdom when visiting Zang organs, and allows food intake when visiting Fu organs. This exit of Wei Qi results in wakefulness. Both sides exit simultaneously and diverge. Upon entering, it descends from Taiyang and Yang Qiao meridians to Yin Qiao, enters the Kidney from the Shaoyin division, causing the eyes to close and sleep to occur. Sleep involves no use of the five sense organs or Yang meridians, no use of hands and feet or their meridians, and no need for food or interaction with Fu organs. It simply cycles from Kidney to Heart, Heart to Lung, Lung to Liver, Liver to Spleen, and Spleen back to Kidney. Although it enters the Zang internally, if the external meridians are not utilized, it cannot attach to solidity to generate clarity but wanders in emptiness to create dreams. Night dreams often reflect daytime activities due to the habituation of Wei Qi. Sleep-talking is similar. This entry of Wei Qi results in sleep, with both sides entering simultaneously and converging. If one forces Wei Qi to stay out while it desires to enter Yin for sleep, yawning occurs. The *Nei Jing* states: "Yin draws downward, Yang draws upward; the pulling between Yin and Yang causes yawning."

Fourth, Wei Qi circulation has depths and superficialities. Moving outside the vessels, the *Nei Jing* describes it as protecting the exterior and maintaining solidity, while the *Nan Jing* calls it the "God guarding against pathogens." In the context of Cold Damage transmission involving the Six Jueyin, specific times correspond to different meridian depths: Yin, Mao, Chen hours correspond to three layers of Shaoyang; Si, Wu, Wei hours to one layer of Taiyang; Shen, You, Xu hours to two layers of Yangming; Hai, Zi, Chou hours to four layers of Taiyin; Zi, Chou, Yin hours to five layers of Shaoyin; and Chou, Yin, Mao hours to six layers of Jueyin. Thus, Taiyang Wei Qi is strongest, Shaoyang is initial advancement, Yangming is initial retreat, and the Three Yin are storing/restraining (a method not in *Nan Jing* but found in Zhang Zhongjing's *Shanghan Lun*). Why does the same Wei Qi have wake/sleep cycles and depth variations? The *Suwen* chapter "Shengqi Tongtian Lun" explains: "Yang Qi is like the sun in the sky..." Wakefulness and sleep are like the sun moving south (winter) or north (summer); depth is like sunrise (morning), noon, or sunset (dusk). The *Nei Jing* also details a method of 15-minute intervals for Shaoyang, Taiyang, Yangming, and the Three Yin, offering more precise calculation. Because Wei Qi is fierce and fast, small cycles exist within large cycles, just as compared to the sun.

Fifth, Wei Qi distributes left and right separately. Its circulation rules involve wakefulness/sleep and depth, but not left-right interchange. Upon exiting for wakefulness, both sides exit simultaneously and diverge, so hand/foot and organ movements have no sequence. Upon entering for sleep, both sides converge simultaneously, so stillness has no sequence. Depth distribution is also separate. Thus, Wei Qi moves in left-right distribution. Consequently, diseases at the Wei level on the right do not affect the left, and vice versa. Zhang Zhongjing stated: "Wind injures Wei," referring to this, explaining why stroke uniquely presents with hemiplegia. Li Dongyuan failed to grasp this principle, incorrectly dividing the left as Blood and the right as Qi. Is it true that illness on the left has nothing to do with Qi, and illness on the right nothing to do with Blood? Such shallow views were not refuted by physicians but rather endorsed, which is strange.

The above points are rigorously verified from the *Lingshu*, *Suwen*, *Nan Jing*, and *Jingui Yaolue*. Their application in medical practice has consistently yielded clear effects, hence recorded here.