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Huangdi asked Bo Gao, saying: "I wish to hear about the movement of Wei Qi (Defensive Qi), and how it enters and exits, merging between Yin and Yang. What is the pattern?"

Bo Gao replied: "There are twelve months in a year, and twelve double-hours (Shichen) in a day. Zi and Wu hours form the meridian axis, while Mao and You hours form the latitude axis. The heavens revolve around the Twenty-Eight Lunar Mansions. Each quarter of the sky contains seven mansions, totaling twenty-eight. Fang and Mao mansions form the latitude lines; Xu and Zhang mansions form the meridian lines. (Here, 'Zhang' refers to the Zhang Mansion.) Therefore, from Fang to Bi belongs to Yang, and from Mao to Xin belongs to Yin. Yang governs the day, and Yin governs the night. Thus, Wei Qi circulates through the body fifty times in one day and night. During the day, it travels in the Yang aspect twenty-five times; at night, it travels in the Yin aspect twenty-five times, circulating among the Five Zang Organs.

Therefore, at dawn (Pingdan), when Yin energy is exhausted, Yang Qi emerges from the eyes. When the eyes open, Qi ascends to the head, follows the neck, descends along the Foot-Taiyang Bladder Meridian, runs down the back, and reaches the tip of the little toe. The dispersed branches diverge from the outer canthus of the eye, descend to the Hand-Taiyang Small Intestine Meridian, and reach the lateral side of the little finger. Another dispersed branch diverges from the outer canthus, descends to the Foot-Shaoyang Gallbladder Meridian, and pours into the space between the fourth and fifth toes. Ascending along the lateral aspect of the Hand-Shaoyang Sanjiao Meridian, it descends to the little finger. Another separate branch ascends to the ear, merges anteriorly with the mandibular pulse, pours into the Foot-Yangming Stomach Meridian, descends to the dorsum of the foot, and enters between the five toes. Another dispersed branch descends from the ear, goes to the Hand-Yangming Large Intestine Meridian, enters between the thumb and index finger, and enters the palm. When it reaches the feet, it enters the center of the sole, exits the medial malleolus, descends in the Yin aspect, and finally reunites with the eyes. This completes one cycle. (According to the meaning of this classic, the Three Yang meridians of the hands and feet run simultaneously and merge into the Yin aspect from the Foot-Taiyang and Foot-Yangming meridians at the same time. 'Three Yang' refers to the portions of the Yang meridians; 'Yin aspect' refers to the portions of the Yin meridians.)

Thus, as the sun moves through one lunar mansion (She), the vital Qi circulates once through the body plus 8/10 of the body's length. As the sun moves through two mansions, vital Qi circulates three times plus 6/10. As the sun moves through three mansions, vital Qi circulates five times plus 4/10. As the sun moves through four mansions, vital Qi circulates seven times plus 2/10. As the sun moves through five mansions, vital Qi circulates nine times. As the sun moves through six mansions, vital Qi circulates ten times plus 8/10. As the sun moves through seven mansions, vital Qi circulates twelve times plus 6/10. As the sun moves through fourteen mansions, vital Qi circulates twenty-five times, with an excess fraction equivalent to 2/10 of the body's length. At this point, Yang is exhausted in Yin, and Yin receives the Qi. Initially entering the Yin, it should flow from the Foot-Shaoyin Kidney Meridian into the Kidneys, from the Kidneys into the Heart, from the Heart into the Lungs, from the Lungs into the Liver, from the Liver into the Spleen, and from the Spleen back into the Kidneys, completing one cycle.

Thus, at night, as the sun moves through one mansion, vital Qi circulates once through the Yin Zang organs plus 8/10 of their capacity, similar to the daytime circulation of twenty-five cycles, finally reuniting with the eyes. In one day and night, Yin and Yang combined have excess fractions: 2/10 of the body's length and 2/10 of the Zang organ capacity. Therefore, the timing of people's waking and sleeping varies because these fractional parts do not divide evenly.

Huangdi said: "When Wei Qi moves up and down in the body, if we do not wait for its specific periodic arrival to observe it, how should we apply acupuncture?" (The 'period' mentioned earlier referred to fixed external markers like clothing; here, 'not waiting for a period' means not relying solely on fixed external markers but on the specific timing of Qi arrival. This clarifies acupuncture methods. When Qi is moving, the Six Yang meridians of the hands and feet emerge simultaneously, making it difficult to pinpoint a single location. The 'location' refers to where Qi is most abundant, i.e., where it converges and intersects. 'Origin' and 'entry/exit' refer to the internal-external relationship between body and Zang-Qi. 'Coming and going' specifically refers to the vertical movement of body Qi.)

Bo Gao replied: "The distribution of Qi varies in amount, and days and nights vary in length. Spring, Autumn, Winter, and Summer each have their own distinct patterns. Generally, we take dawn as the reference point and the end of the night as the start. One day and night equals one hundred water-clock beats (Ke). Twenty-five Ke represents half a day (one-quarter of a full day). This is constant without exception. Acupuncture stops at sunset. Following the length of the day, each serves as a reference for acupuncture. We must carefully observe the timing; then disease can be predicted and treated. Losing the timing or acting contrary to the pattern renders all diseases untreatable. Therefore, it is said: To treat Excess conditions, puncture when the Qi arrives; to treat Deficiency conditions, puncture when the Qi departs. This describes observing the presence and absence of Qi to determine Excess or Deficiency before puncturing.

Therefore, carefully observe where the Qi is located and puncture accordingly; this is called 'meeting the time.' If the disease is in the Three Yang meridians, wait until the Qi is in the Yang aspect to puncture. If the disease is in the Three Yin meridians, wait until the Qi is in the Yin aspect to puncture.

At the first Ke after midnight, Vital Qi is in the Foot-Taiyang [Bladder].
At the second Ke, Vital Qi is in the Foot-Shaoyang [Gallbladder].
At the third Ke, Vital Qi is in the Foot-Yangming [Stomach].
At the fourth Ke, Vital Qi is in the Yin aspect.
At the fifth Ke, Vital Qi is in the Foot-Taiyang [Bladder].
At the sixth Ke, Vital Qi is in the Foot-Shaoyang [Gallbladder].
At the seventh Ke, Vital Qi is in the Foot-Yangming [Stomach].
At the eighth Ke, Vital Qi is in the Yin aspect.
At the ninth Ke, Vital Qi is in the Foot-Taiyang [Bladder].
At the tenth Ke, Vital Qi is in the Foot-Shaoyang [Gallbladder].
At the eleventh Ke, Vital Qi is in the Foot-Yangming [Stomach].
At the twelfth Ke, Vital Qi is in the Yin aspect.
At the thirteenth Ke, Vital Qi is in the Foot-Taiyang [Bladder].
At the fourteenth Ke, Vital Qi is in the Foot-Shaoyang [Gallbladder].
At the fifteenth Ke, Vital Qi is in the Foot-Yangming [Stomach].
At the sixteenth Ke, Vital Qi is in the Yin aspect.
At the seventeenth Ke, Vital Qi is in the Foot-Taiyang [Bladder].
At the eighteenth Ke, Vital Qi is in the Foot-Shaoyang [Gallbladder].
At the nineteenth Ke, Vital Qi is in the Foot-Yangming [Stomach].
At the twentieth Ke, Vital Qi is in the Yin aspect.
At the twenty-first Ke, Vital Qi is in the Foot-Taiyang [Bladder].
At the twenty-second Ke, Vital Qi is in the Foot-Shaoyang [Gallbladder].
At the twenty-third Ke, Vital Qi is in the Foot-Yangming [Stomach].
At the twenty-fourth Ke, Vital Qi is in the Yin aspect.
At the twenty-fifth Ke, Vital Qi is in the Foot-Taiyang [Bladder]. This concludes the half-day cycle.

From the Fang Mansion to the Bi Mansion covers fourteen mansions. Water flows fifty Ke, and the sun moves half the celestial sphere. For every mansion the sun traverses, water flows three Ke and 7/15 of a Ke (approx. 0.857 Ke, with remainders). (Calculated by 15 fen per Ke, 7/15 is approx 8.57 fen... still with remainders. The 'Fifty Circulations' chapter mentions that at 4 Ke, the sun travels 40 fen, which is one mansion plus 1/9 of a She, also with remainders. Thus, generally adding the date to the mansion position—where Vital Qi is in Taiyang—is only an approximation, not a precise rate.)

The general principle states: Usually, based on the sun's position relative to the mansions, Vital Qi is in the Foot-Taiyang [Bladder]. Therefore, as the sun moves through one mansion, Vital Qi circulates through the Three Yang meridians and the Yin aspect. (The character 'circulate' here differs slightly from the earlier usage, though confusion remains inevitable.) Continue thus without end; Heaven and Earth follow the same rhythm, complex and endless, beginning and ending anew. One day and night, water flows one hundred Ke and finishes. (Water clocks are used as the primary measure because their numbers align without fractional remainders.)

This passage elucidates clear and pure Qi flowing smoothly. Its brilliance lies in narrating factual events through discursive reasoning, transforming rigidity into vitality, handling heavy matters with lightness. How divine and courageous is this!

The description of Wei Qi's movement in this chapter seems illogical. Therefore, Dai Tongfu considered the text following 'At the first Ke... Vital Qi is in Foot-Taiyang' as interpolations (later additions). He argued it should read 'One Ke in Three Yang, Two Ke in Three Yin' to fit the number of two Ke per cycle. This captures only one aspect. The classic's front and back sections were originally two separate parts. The front describes Wei Qi emerging from the eyes, descending Foot-Taiyang, its dispersed branches going to Hand-Taiyang and Foot-Shaoyang, ascending Hand-Shaoyang, its separate branch going to Foot-Yangming, its dispersed branch going to Hand-Yangming, and stating that upon reaching the feet, it enters the Yin aspect from the sole. This indicates the Three Yang meridians of hands and feet run simultaneously without sequence, merging into the Yin aspect from Foot-Taiyang and Foot-Yangming together. Where is there a sequence of 'One Ke Taiyang, Two Ke Shaoyang, Three Ke Yangming'? And where is there waiting until the fourth Ke to enter the Yin aspect? Dai's theory of 'One Ke Three Yang, Two Ke Three Yin' is incorrect. It should state 'One Ke circulates through Three Yang, Two Ke circulates through Three Yin,' not 'is in Three Yang/Yin.' The latter part describes Wei Qi moving up and down in the body with regular periods, which is about observing its location for acupuncture—a different meaning entirely unrelated to the previous text. Although the acupuncture method is lost, the textual meaning remains; with calm reflection, one can discern it. Furthermore, the references to Hand/Foot Taiyang, Shaoyang, and Yangming refer to anatomical regions/portions, not specific meridians. The Yin and Yang aspects collectively refer to daytime circulation in Yang (exterior) and nighttime circulation in Yin (interior/Zang organs)."