黄帝问于岐伯曰。余闻人之合于天道也。内有五脏。以应五音五色五时五味五位也。外有六腑。
以应六律。六律建阴阳诸经。而合之十二月。十二辰。十二节。十二经水。十二时。十二经脉者。
此五脏六腑之所以应天道。夫十二经脉者。人之所以生。病之所以成。人之所以治。病之所以起。
学之所始。工之所止也。粗之所易。上之所难也。请问其离合出入奈何。岐伯稽首再拜曰。明乎哉
问也。此粗之所过。上之所息也。请卒言之。
此论十二经脉。十五大络之外。而又有经别也。五位。五方之定位。六律建阴阳者。创建六阴
六阳以合诸经。诸经者。十二经脉。十二大络。十二经别也。六律分立阴阳。是以合天之十二月。
十二节。十二时。合地之十二经水。人之十二经脉。此五脏六腑之所以应天道也。夫六脏脉属脏络
腑。六腑脉属腑络脏。此荣血之流行于十二经脉之中。然经脉之外。又有大络。大络之外。又有经别。
是以粗工为易。而上工之所难也。离合者。谓三阳之经。别离本经而合于三阴。三阴之经。别离本
经而合于三阳。此即缪刺篇所当巨刺之经。左盛则右病。右盛则左病。如此者。必巨刺之。必中其
经。非络脉也。按、上章之所谓别者。言十二经脉之外。而有别络。此章之所谓别者。言十二经脉
之外。而又有别经。此人之所以生此阴阳血气。病之所以成是动所生。及大络
之奇病。经别之移易。治之所以分皮刺经刺缪刺巨刺也。所生之经络多歧。所成之病证各别。所治
之刺法不同。故上工之所难也。尚御公曰。五脏为阴。六腑为阳。阳者。天气也。主外。阴者。地
气也。主内。本篇以六腑应六律。以合阴阳诸经。盖五脏内合六腑。六腑外合十二经脉。故曰五脏
六腑之所以应天道。朱永年曰。五营运论云。在脏为肝。在体为筋。在脏为肺。在体为皮。是五
脏之外合于皮肉筋骨也。本脏篇曰。肺合大肠。大肠者。皮其应。心合小肠。小肠者。脉其应。是
五脏内合六腑。六腑外合于皮肉筋骨也。五脏六腑。雌雄相合。离合之道。通变无穷。高士宗曰。
太始天元册文曰。太虚寥廓。肇基化元。布气真灵。总统坤元。盖太始太虚者。乃空玄无极之境。
由无极而生太极。太极而分两仪。人虽本天地所生。而统归于天道。
足太阳之正。别入于 中。其一道下尻五寸。别入于肛。属于膀胱。散之肾。循膂当心入散。
直者从膂上出于项。复属于太阳。此为一经也。足少阴之正。至 中。别走太阳而合。上至肾。当
十四椎出属带脉。直者系舌本。复出于项。合于太阳。此为一合。成以诸阴之别。皆为正也。
此足太阳与足少阴为一合也。正者。谓经脉之外。别有正经。非支络也。足太阳之正。从经脉
而别入于 中。其一道者。经别之又分两歧也。尻、肫也。肛乃大肠之魄门。别入于肛者。别从
肛门而入属于膀胱。散之肾。复循脊膂上行。当心而散。其直行者。从背膂上出于项。复属于太
阳之经脉。此为一经别也。盖从经而别行。复属于太阳之经脉。故名经别。谓经脉之别经也。足少
阴之正。至 中。别走于太阳之部分。而与太阳之正相合。上行至肾。当脊之十四椎处。外出而属
于带脉。其直行者。从肾上系舌本。复出于项。与太阳上出于项之
经。正相合于项间。以为一合也。阴阳离合论曰。阳予之正。阴为之主。少阴之上。名曰太阳。
太阴之前。名曰阳明。厥阴之表。名曰少阳。谓阳乃阴与之正。而阴为之主。阳本于阴之所生。故
曰成以诸阴之别。谓三阳之经正。合于三阴。以成手足三阴之经别。此三阳乃归于三阴之正。故曰
皆为正也。是以三阳之别。外合于三阴之经。而内合于五脏。三阴之别。只合三阳之经。而不合于
六腑也。尚御公曰。按十二经脉之荣气流行。六阴脉属脏络腑。六阳脉属腑络脏。本篇三阴之经别。
上至肾属心走肺。而皆不络于六腑。又如足太阳之脉。循膂络肾。膀胱之经别。则别入于肛。属膀
胱。散之肾。足少阴肾脉。贯脊属肾络膀胱。其经别至 中。别走太阳而上至肾。又出属带脉。而
复出于项。手少阴心脉。起于心中。出络心系。下膈络小肠。其经别入于渊液两筋之间。属于心。
手厥阴心包络之脉。起于胸中。出属心包。下膈历络三焦。而经别下渊液三寸。入胸中。别属三焦。
手太阴肺脉。起于中焦。下络大肠。还循胃口。上膈属肺。其经别入渊液少阴之前。入走肺。散之
太阳。此经脉与经别出入不同。各走其道。而马氏以正为正经。宜经脉篇之直行者相合。别者为络。
宜与经脉篇之其支者其别者相合。噫。经脉血气之生始出入。头绪纷纭。不易疏也。
足少阳之正。绕髀入毛际。合于厥阴。别者入季胁之间。循胸里属胆散之。上肝贯心。以上挟
咽。出颐颔中。散于面。系目系。合少阳于目外 。足厥阴之正。别跗上。上至毛际。合于少阳。
与别俱行。此为二合也。
按、足少阳之脉。起于目锐 。循头面而下行于足跗。少阳之别。绕髀上行。至目锐 。而合
于少阳之经。是经脉与经别。交相逆顺而行者也。足厥阴之正。别行于跗上。上至毛际。而合少阳。
与少阳之别。合而偕行。此为
二合也。尚御公曰。与阳俱行。谓三阴之别。合于三阳之别俱行。而阳别成诸阴之别矣。故曰成
以诸阴之别。诸、语助辞。
足阳明之正。上至髀。入于腹里。属胃散之脾。上通于心。上循咽。出于口。上额颅。还系目系。
合于阳明也。足太阴之正。上至髀。合于阳明。与别俱行。上结于咽。贯舌中。此为三合也。
股内为髀。伏兔后为髀关。足阳明之正。从足跗而上至髀。从腹胸而上行头面。合手阳明之经
脉于目下承泣四白之间。盖亦与经脉相逆顺而行也。足太阴之正。别经脉而走阳明之髀分。与阳明
之正。相合而偕行。上结于喉。贯舌中。此为三合也。
手太阳之正。指地别于肩解。入腋走心。系小肠也。手少阴之正。别入于渊液两筋之间。属于
心。上走喉咙。出于面。合目内 。此为四合也。
阴阳系日月论曰。天为阳。地为阴。日为阳。月为阴。其合于人也。腰以上为天。腰以下为地。
足之十二经脉。以应十二月。月生于水。故在下者为阴。手之十指。以应十日。日主火。故在上
者为阳。手太阳之正指地者。谓手之太阳。下合于足太阳也。盖在脏腑十二经脉。有手足之分。论
阴阳二气。只有三阴三阳。而无分手与足矣。故六腑皆出于足之三阳。上合于手。是以手少阴之正。
上出于面。亦与足太阳相合于目内 之睛明。水火上下之相交也。夫手太阳少阴。皆属于火。天一
生水。地二生火。火上水下。阴阳互交。故手太阳指地而下交于足。手少阴上行而合于膀胱之经。
论天地水火。有上下之相交。归于先天。合为一气。故人之脏腑经脉。所以应天道也。
手少阳之正。指天别于巅。入缺盆。下走三焦。散于胸中也。手心主之正。别下渊液三寸。
入胸中。别属三焦。出循喉咙。出耳后。合少阳完骨之下。此为五合也。
少阳、初阳也。从阴而生。自下而上。故曰手少阳之正者。谓手合于足也。曰指天者。谓足
合于手也。论少阳心主二经。则为六合。论阴阳之气。只三合矣。巅乃督脉之会。督脉应天道之
环转一周。故从巅而别下入缺盆。走三焦而散于胸中也。渊液。胆经穴。在腋下三寸。手心主之正。
别经脉而下行于渊液之分。下渊液三寸。以入胸中。别属三焦。出循喉咙。上出耳后。合少阳经别
于完骨之下。此为五合也。
手阳明之正。从手循膺乳。别于肩 。入柱骨下。走大肠属于肺。上循喉咙。入缺盆。合于阳
明也。手太阴之正。别入渊液少阴之前。入走肺。散之太阳。上出缺盆。循喉咙。复合阳明。此六
合也。
手阳明之正。从手之经脉。循膺乳间而别行。上于肩 。入柱骨下。走大肠。属于肺。复上循
喉咙。出缺盆。而与手阳明之经脉相合也。手太阴之正。别经脉于天府云门之际。入渊液之分。行
太阴之前。入走肺。于当心处散之太阳。复上出缺盆。循喉咙。与少阳之正相合。此为六合也。夫
阴阳六合。始于足太阳。而终于手太阴。复散之太阳。盖亦周而复始也。尚御公曰。肺主天。膀胱
为水府。肺者。太阴也。皆积水也。始于足太阳。而终于手太阴。周而复始。应天道之司天在泉。
六气环转之不息。
Huangdi asked Qibo: I have heard that the human body corresponds to the Heavenly Dao. Internally, there are five Zang organs corresponding to the five tones, five colors, five seasons, five flavors, and five positions (five directions); externally, there are six Fu organs corresponding to the six musical pitches (Lü). The six Lü establish Yin and Yang meridians, which combine with twelve months, twelve Earthly Branches, twelve solar terms, twelve major rivers, and twelve double-hour periods. These twelve primary meridians are how the five Zang and six Fu organs correspond to the Heavenly Dao. The twelve primary meridians are the basis of human life, the cause of disease formation, the means of healing, the signs of disease onset, the beginning of learning, and the boundary between skilled and unskilled practitioners. Crude physicians tend to overlook them, while superior physicians find them difficult to master. May I ask about their separation, joining, entry, and exit?
Qibo bowed twice and said: Your question is very clear! This is what crude physicians often pass over, and what superior physicians ponder deeply. Let me conclude my explanation.
This section discusses that beyond the twelve primary meridians and fifteen great collaterals, there are also "Jingbie" (Branch Meridians). The term "five positions" refers to the fixed locations of the five directions. "The six Lü establish Yin and Yang" means establishing six Yin and six Yang to coordinate with various meridians. The term "various meridians" includes the twelve primary meridians, twelve great collaterals, and twelve Jingbie. The six Lü divide Yin and Yang; thus, they correspond to Heaven's twelve months, twelve solar terms, and twelve double-hour periods, and to Earth's twelve major rivers and humans' twelve primary meridians. This is how the five Zang and six Fu organs correspond to the Heavenly Dao. The pulses of the six Yin organs belong to the Zang and connect to the Fu; the pulses of the six Fu organs belong to the Fu and connect to the Zang. This describes the circulation of Ying (Nutrient) blood within the twelve primary meridians. However, outside the primary meridians, there are great collaterals; outside the great collaterals, there are Jingbie. Therefore, crude physicians consider it easy, while superior physicians find it difficult. The term "separation and joining" refers to the fact that the Jingbie of the three Yang meridians separate from their primary meridians and join the three Yin meridians, while the Jingbie of the three Yin meridians separate from their primary meridians and join the three Yang meridians. This is the meridian system referred to in the *Miao Ci* chapter where "Ju Ci" (Giant Puncture) should be applied. When excess is on the left, disease appears on the right; when excess is on the right, disease appears on the left. In such cases, Ju Ci must be used, targeting the primary meridians, not the collateral vessels. Note: In the previous chapter, "bie" referred to "Bieluo" (Collateral Vessels) outside the twelve primary meridians; in this chapter, "bie" refers to "Biejing" (Branch Meridians) outside the twelve primary meridians. This explains why humans generate these Yin-Yang and Qi-Blood, why diseases form as "Shi Dong" (Moving) and "Suo Sheng" (Generated) conditions, and why treatments differ into skin puncture, meridian puncture, Miao Ci, and Ju Ci. The resulting meridians are complex, the formed diseases are distinct, and the puncture methods vary, making it difficult for superior physicians. Shang Yugong stated: The five Zang are Yin, and the six Fu are Yang. Yang represents Heavenly Qi and governs the exterior; Yin represents Earthly Qi and governs the interior. This chapter uses the six Fu to correspond to the six Lü, combining with Yin-Yang meridians. Generally, the five Zang internally combine with the six Fu, and the six Fu externally combine with the twelve primary meridians. Hence, it is said that the five Zang and six Fu correspond to the Heavenly Dao. Zhu Yongnian stated: In the *Wu Yun Xing Da Lun*, it says: In the Zang, it is Liver; in the tissues, it is Sinews; in the Zang, it is Lung; in the tissues, it is Skin. This shows the external combination of the five Zang with skin, flesh, sinews, and bones. In the *Ben Zang* chapter, it says: Lung combines with Large Intestine, and Large Intestine corresponds to skin; Heart combines with Small Intestine, and Small Intestine corresponds to vessels. This shows the internal combination of the five Zang with the six Fu, and the external combination of the six Fu with skin, flesh, sinews, and bones. The five Zang and six Fu combine in male-female pairs, and the way of separation and joining involves infinite variations. Gao Shzong stated: In the *Tai Shi Tian Yuan Ce Wen*, it says: The Great Void is vast and empty, initiating the foundation of transformation and origin, distributing true spiritual Qi, commanding the Kun Yuan. The Tai Shi and Great Void refer to the realm of emptiness and non-existence. From non-existence arises Tai Ji, and Tai Ji divides into Liang Yi. Although humans originate from Heaven and Earth, they ultimately return to the Heavenly Dao.
The Zheng (Regular) branch of Foot-Taiyang enters the popliteal fossa. One path descends five cun below the sacrum, enters the anus, belongs to the Bladder, and scatters to the Kidney. It follows the paravertebral muscles upward, dispersing at the heart level. The straight path ascends from the paravertebral muscles, emerges at the nape, and re-joins the Foot-Taiyang meridian. This constitutes one meridian branch. The Zheng branch of Foot-Shaoyin reaches the popliteal fossa, diverges to Foot-Taiyang, and joins it. It ascends to the Kidney, exits at the level of the fourteenth thoracic vertebra to belong to the Dai Mai (Girdle Vessel). The straight path connects to the root of the tongue, emerges at the nape, and joins Foot-Taiyang. This forms one union. Thus, all branches of Yin meridians are called "Zheng." This is the first union between Foot-Taiyang and Foot-Shaoyin. "Zheng" means a regular meridian existing outside the primary meridian, distinct from collateral branches. The Zheng branch of Foot-Taiyang diverges from the primary meridian into the popliteal fossa. That branch represents a further division of the Jingbie. "Kao" refers to the popliteal fossa. The anus is the魄门 (Gate of Essence) of the Large Intestine. Diverging into the anus means entering via the anus to belong to the Bladder, scattering to the Kidney, then ascending along the spinal muscles, dispersing at the heart. The straight path ascends from the back muscles, emerges at the nape, and re-joins the Taiyang primary meridian. This is one Jingbie. Since it diverges from the primary meridian and re-joins the Taiyang meridian, it is named Jingbie, meaning the branch meridian of the primary meridian. The Zheng branch of Foot-Shaoyin reaches the popliteal fossa, diverges to the region of Taiyang, and joins its Zheng branch. It ascends to the Kidney, exits at the fourteenth thoracic vertebra to belong to the Dai Mai. The straight path ascends from the Kidney to connect to the root of the tongue, emerges at the nape, and joins the Taiyang path emerging at the nape in the neck region, forming one union. The *Yin Yang Li He Lun* states: Yang provides the correct energy to Yin, and Yin acts as the master. Above Shaoyin is named Taiyang; before Taiyin is named Yangming; on the surface of Jueyin is named Shaoyang. This means Yang is the correct energy given by Yin, and Yin is its master. Yang originates from Yin, hence it is said "formed by the branches of all Yin." It implies that the Zheng branches of the three Yang meridians join the three Yin to form the Jingbie of the hand and foot Yin meridians. Since these three Yang return to the Zheng of the three Yin, it is said "all are Zheng." Therefore, the branches of the three Yang externally join the three Yin meridians and internally join the five Zang; the branches of the three Yin only join the three Yang meridians and do not join the six Fu. Shang Yugong stated: According to the circulation of Ying Qi in the twelve primary meridians, the six Yin pulses belong to Zang and connect to Fu, while the six Yang pulses belong to Fu and connect to Zang. In this chapter, the Jingbie of the three Yin ascend to the Kidney, belong to the Heart, and travel to the Lung, without connecting to the six Fu. For example, the Foot-Taiyang pulse follows the spinal muscles to connect to the Kidney; the Jingbie of the Bladder diverges into the anus, belongs to the Bladder, and scatters to the Kidney. The Foot-Shaoyin Kidney pulse penetrates the spine, belongs to the Kidney, and connects to the Bladder; its Jingbie reaches the popliteal fossa, diverges to Taiyang, ascends to the Kidney, exits to belong to the Dai Mai, and re-emerges at the nape. The Hand-Shaoyin Heart pulse originates in the heart, exits to connect to the heart system, descends through the diaphragm to connect to the Small Intestine; its Jingbie enters between the two tendons at Yuanye, belonging to the Heart. The Hand-Jueyin Pericardium pulse originates in the chest, exits to belong to the Pericardium, descends through the diaphragm to connect sequentially to the Sanjiao; its Jingbie descends three cun below Yuanye, enters the chest, and separately belongs to the Sanjiao. The Hand-Taiyin Lung pulse originates in the middle jiao, descends to connect to the Large Intestine, returns to follow the stomach opening, ascends through the diaphragm to belong to the Lung; its Jingbie enters before Yuanye and the Shaoyin, travels to the Lung, and scatters to Taiyang. These primary meridians and Jingbie have different paths of entry and exit, each following its own route. Ma Shi considered "Zheng" as the regular primary meridian, suitable for matching the straight paths in the *Jing Mai* chapter; "Bie" as collaterals, suitable for matching the branches and divergences in the *Jing Mai* chapter. Alas, the generation, origin, entry, and exit of Qi and Blood in the meridians are complicated and difficult to sort out.
The Zheng branch of Foot-Shaoyang winds around the thigh, enters the pubic region, and joins Jueyin. Another branch enters the space between the lower ribs, follows the interior of the chest, belongs to the Gallbladder and scatters, ascends to the Liver, pierces the Heart, ascends to flank the throat, emerges in the jaw area, scatters on the face, connects to the eye system, and joins Shaoyang at the outer canthus. The Zheng branch of Foot-Jueyin diverges above the dorsum of the foot, ascends to the pubic region, and joins Shaoyang, traveling together with its branch. This is the second union.
Note: The Foot-Shaoyang pulse originates at the outer canthus, follows the head and face, and descends to the dorsum of the foot. The Shaoyang branch winds around the thigh upward, reaches the outer canthus, and joins the Shaoyang meridian. This shows the primary meridians and Jingbie traveling in opposite directions. The Zheng branch of Foot-Jueyin diverges above the dorsum of the foot, ascends to the pubic region, and joins Shaoyang, traveling together with the Shaoyang branch. This is the second union. Shang Yugong stated: "Traveling together with Yang" means the branches of the three Yin join the branches of the three Yang to travel together, and the branches of Yang complete the branches of Yin. Hence, it is said "formed by the branches of all Yin." "All" is a particle.
The Zheng branch of Foot-Yangming ascends to the thigh, enters the abdominal cavity, belongs to the Stomach and scatters to the Spleen, connects upward to the Heart, follows the throat upward, emerges from the mouth, ascends to the forehead and skull, returns to connect to the eye system, and joins Yangming. The Zheng branch of Foot-Taiyin ascends to the thigh, joins Yangming, travels together with its branch, knots at the throat, and pierces the middle of the tongue. This is the third union.
The inner thigh is the thigh (Bi). Behind Futu is Bigan. The Zheng branch of Foot-Yangming ascends from the dorsum of the foot to the thigh, travels up from the abdomen and chest to the head and face, and joins the Hand-Yangming meridian between Chengqi and Sibai below the eyes. It likely travels in opposition to the primary meridian. The Zheng branch of Foot-Taiyin diverges from the primary meridian to the thigh region of Yangming, joins the Zheng branch of Yangming to travel together, knots at the throat, and pierces the tongue. This is the third union.
The Zheng branch of Hand-Taiyang points downward, diverges at the shoulder joint, enters the axilla, travels to the Heart, and connects to the Small Intestine. The Zheng branch of Hand-Shaoyin diverges into the space between the two tendons at Yuanye, belongs to the Heart, travels upward to the throat, emerges on the face, and joins at the inner canthus. This is the fourth union.
The *Yin Yang Xi Ri Yue Lun* states: Heaven is Yang, Earth is Yin; the Sun is Yang, the Moon is Yin. Corresponding to humans, the upper body is Heaven, and the lower body is Earth. The twelve meridians of the feet correspond to the twelve months. The Moon is born from Water, so those below are Yin. The ten fingers of the hands correspond to the ten Days. The Sun governs Fire, so those above are Yang. The Hand-Taiyang Zheng "pointing downward" means Hand-Taiyang joins Foot-Taiyang below. Generally, among the twelve meridians of Zang and Fu, there is a distinction between hand and foot; but when discussing Yin-Yang Qi, there are only Three Yin and Three Yang, without distinguishing hand and foot. Thus, all six Fu originate from the three Yang of the feet and join the hands upward. Therefore, the Hand-Shaoyin Zheng emerges upward on the face and also joins Foot-Taiyang at Jingming in the inner canthus. This is the mutual interaction of Water and Fire above and below. Both Hand-Taiyang and Hand-Shaoyin belong to Fire. One generates Water, Two generates Fire. Fire is above, Water is below, and Yin-Yang interact mutually. Thus, Hand-Taiyang points downward to join the foot, and Hand-Shaoyin ascends to join the Bladder meridian. Discussing Heaven, Earth, Water, and Fire, there is mutual interaction above and below, returning to the Pre-Heaven state, combining into one Qi. Thus, the meridians of human Zang and Fu correspond to the Heavenly Dao.
The Zheng branch of Hand-Sanjiao points upward, diverges at the vertex, enters the supraclavicular fossa, descends to travel through the Sanjiao, and scatters in the chest. The Zheng branch of Hand-Zhujin (Pericardium) diverges three cun below Yuanye, enters the chest, separately belongs to the Sanjiao, exits following the throat, emerges behind the ear, and joins Shaoyang below Wanggu. This is the fifth union.
Shaoyang is the initial Yang. It is born from Yin and rises from below; hence, the Zheng branch of Hand-Sanjiao is described as "Hand joining Foot." To say "points upward" means "Foot joining Hand." Discussing the Shaoyang and Zhujin meridians results in six unions; discussing Yin-Yang Qi results in only three unions. The vertex is the meeting point of the Du Mai, which corresponds to the cyclical rotation of the Heavenly Dao. Thus, it diverges from the vertex, enters the supraclavicular fossa, travels through the Sanjiao, and scatters in the chest. Yuanye is an acupoint of the Gallbladder meridian, located three cun below the armpit. The Zheng branch of Hand-Zhujin diverges from the primary meridian, descends to the region of Yuanye, goes three cun below Yuanye to enter the chest, separately belongs to the Sanjiao, exits following the throat, emerges behind the ear, and joins the Shaoyang Jingbie below Wanggu. This is the fifth union.
The Zheng branch of Hand-Yangming follows the chest and breast from the hand, diverges at Jianyu, enters below the vertebral column, travels to the Large Intestine, belongs to the Lung, follows the throat upward, enters the supraclavicular fossa, and joins Yangming. The Zheng branch of Hand-Taiyin diverges before Yuanye and Shaoyin, travels to the Lung, scatters to Taiyang, emerges from the supraclavicular fossa, follows the throat, and re-joins Yangming. This is the sixth union.
The Zheng branch of Hand-Yangming follows the intercostal and breast regions from the hand's primary meridian, diverges, ascends to Jianyu, enters below the vertebral column, travels to the Large Intestine, belongs to the Lung, ascends again to follow the throat, emerges from the supraclavicular fossa, and joins the Hand-Yangming primary meridian. The Zheng branch of Hand-Taiyin diverges from the primary meridian between Tianfu and Yunmen, enters the region of Yuanye, travels before Taiyin, enters the Lung, scatters to Taiyang at the heart level, emerges from the supraclavicular fossa, follows the throat, and joins the Zheng branch of Shaoyang. This is the sixth union. The six unions of Yin and Yang begin with Foot-Taiyang and end with Hand-Taiyin, then scatter to Taiyang again. This is a cycle repeating itself. Shang Yugong stated: The Lung governs Heaven, and the Bladder is the reservoir of Water. The Lung is Taiyin and both accumulate water. Beginning with Foot-Taiyang and ending with Hand-Taiyin, cycling repeatedly, it corresponds to the Si Tian and Zai Quan of the Heavenly Dao and the ceaseless rotation of the Six Qi.