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The undifferentiated unity of the Great Dao cannot be known in its origin. However, the highest Dao, without words, cannot clarify its principles; the grandest form, without symbols, cannot measure its profundity. The subtlety of Dao and Xiang (symbol/image) cannot be elucidated without language. Let us attempt to trace the origin of the Mai (Pulse/Vessel). What is it? It is neither Qi (Vital Energy) nor Blood. It moves ceaselessly: Ying Qi (Nutritive Energy) circulates within the Mai, while Wei Qi (Defensive Energy) circulates outside. As stated in the Classics: "The Mai is the residence of Blood." From the *Suwen* down to the present, there are no records in the classics, nor biographies mentioning its name. Yet, its mysteries are profound, and the sage's intent is subtle. Even brilliant and wise scholars cannot easily comprehend it. What exactly is the Mai? The Mai has three names: first, the root of life; second, the spirit of Qi; third, the path of form. This corresponds to what the Classics call "Heavenly Harmony" (Tian He). To break a limb or blind both eyes causes no harm, but one cannot live for even a moment without the Mai; losing it means death. The Classics state: In Spring, the pulse is Xian (Wiry); (alternatively described as Chang/Long). In Summer, the pulse is Hong (Surging); (alternatively described as Gou/Hook). In Autumn, the pulse is Mao (Feather-like); (alternatively described as Se/Rough). In Winter, the pulse is Shi (Stone-like); (alternatively described as Chen/Deep). These describe the normal pulse, which aligns with the primordial creative Qi of nature, circulating through the four seasons and corresponding to the positions of Wood, Fire, Water, and Metal, governing growth, flourishing, harvesting, and storage. Thus, born from the yin and yang of heaven and earth, it is inseparable from Qi, providing signs of life and death in the pulse. The Classics say: "The Mai is the residence of Blood." It is like the capital city in the world, where prefectures and counties have government offices. The state establishes these offices to prevent villains from committing illegal acts. If the offices were not established, the virtuous would have no way to redress grievances, and the wicked would not be punished for their crimes. Yin and yang would mix, sages and fools would intermingle, leading to chaos. The Classics state: "The Five Movements and Yin-Yang are the Way of Heaven and Earth, the guidelines of all things, the parents of change, the beginning of life and death, and the residence of spiritual enlightenment." Since Yin-Yang is the residence of spiritual enlightenment, and the Mai is the residence of Blood, this is clearly visible. Without the Mai, Blood cannot circulate through the meridians and body parts, becoming turbulent and either dispersing or gathering. Without the Mai, Qi cannot move through sinews, bones, zang-fu organs, and up and down, potentially causing sudden collapse or syncope. Therefore, the Classics say: "If entry and exit cease, the Spirit Mechanism perishes; if ascent and descent stop, the Qi Establishment stands alone in danger." Thus, when Qi transforms, things are born; when Qi changes, things alter; when Qi is abundant, things grow strong; when Qi is weak, things decline; when Qi is exhausted, things die; when Qi is balanced, things are harmonious; when Qi is chaotic, things become diseased. All changes follow the abundance or deficiency of Qi.

The character "Mai" consists of components meaning flesh, eternity, claw/nail, and blood. With this true primordial Qi, the limbs and bones, flesh and blood, sinews and bones, nails and hair flourish and can rely on it for growth, enduring eternally. Hence, the components of flesh and eternity refer to this. The components of claw and blood indicate that it circulates like water, branching out to cover the whole body, with no blockage. The *Shiming* states: "Mai means curtain/mask." Like a curtain covering, it integrates the form of the body, guiding the True Primordial Qi of Taiyi. Primordial Qi, in terms of Qi, is neither cold nor hot, neither warm nor cool. In terms of the Mai, it is neither wiry, surging, rough, nor deep. It does not float or sink due to Qi, nor flow or stagnate due to Blood; it is the naturally harmonious Qi. Thus, spring warmth, summer heat, autumn coolness, and winter cold occur because Primordial Qi moves ceaselessly, circulating through the positions of Wood, Fire, Water, and Metal, driving the transformations of temperature and seasons, continuously generating new life without pause, as days and months alternate and seasons shift, yet the pulse never rests. After humans acquire their physical form and the five Zang organs are formed, the internal Primordial Qi arises. Thus, the wiry, surging, feather-like, and stone-like pulses correspond to the Qi of the four seasons, within which the Mai resides. The *Dao De Jing* states: "Look at it, but do not see it; listen to it, but do not hear it; grasp it, but do not hold it. Meet it, but do not see its front; follow it, but do not see its back." This describes the Mai. It also says: "Mold clay to make a vessel; it is the emptiness inside that makes the vessel useful. Therefore, 'being' provides convenience, but 'non-being' provides function." It further says: "I do not know its name, so I call it Dao; forcing a name upon it, I call it Great." This is the original intent behind naming the Mai. Thus, Dao is the mystery of all things; Mai is the spirit of all bones. The subtlety of mystery and spirit is the same as Primordial Qi, which exists in every vessel and reaches everywhere. Blood flows because of it, and Qi generates because of it. Thus, Ying Qi circulates within the Mai, and Wei Qi circulates outside. Looking forward, it seems ahead; suddenly it is behind, yet it never depletes—all due to the Mai. Separately speaking, there is Qi, Blood, and Mai; collectively speaking, only the Mai circulates and manages Qi and Blood. Therefore, the Classics state: "Qi and Blood are the spirit of man. They must be carefully nurtured." The *Yin Yang Bie Lun* states: "What is called Yang is the Yang of the Stomach cavity." This Yang refers to the Mai. The Stomach belongs to Earth. The Mai is the creatively transformative Qi of nature. If Earth had no Qi, how could it grow, flourish, harvest, and store? If Qi had no Earth, how could it nourish and transform all things? There would be no generation or destruction. The Qi of a healthy person constantly receives support from the Stomach. The *Zheng Li Lun* states: "When food enters the Stomach, the Mai channels begin to flow. Yin and Yang intersect; when the Stomach is harmonious, the Mai moves. Humans receive the rhythms of Heaven and Earth." Thus, in Spring, a slight wiry quality with Stomach Qi indicates health; a wiry pulse without Stomach Qi indicates death. In Summer, a slight hook quality with Stomach Qi indicates health; a hook pulse without Stomach Qi indicates death. In Late Summer, a slight soft quality with Stomach Qi indicates health; a weak pulse without Stomach Qi indicates death. In Autumn, a slight feather-like quality with Stomach Qi indicates health; a feather-like pulse without Stomach Qi indicates death. In Winter, a slight stone-like quality with Stomach Qi indicates health; a stone-like pulse without Stomach Qi indicates death.

Yin refers to the True Zang Pulse. Its appearance signifies deterioration, and deterioration leads inevitably to death. The Five Zang organs belong to Yin. When the Liver pulse arrives, it is central without exterior, urgent like touching a blade, sounding like pressing a lute string. When the Heart pulse arrives, it is firm and beating, like rolling coix seeds. When the Lung pulse arrives, it is large and empty, like feathers brushing the skin. When the Kidney pulse arrives, it beats and cuts off, like fingers tapping on stone. The Spleen pulse is weak and occasionally rapid, occasionally slow. Such pulses represent the exclusive manifestation of Zang pulses without Stomach Qi. When all five Zang pulses arrive in isolation and cut off, death ensues. Therefore, the Classics state: "Distinguishing Yang allows one to know the contraindicated times for disease; distinguishing Yin allows one to know the time of life and death." Human constitutions vary—restless, rapid, slow, weak, long, short, thick-skinned, fleshy—and the pulse responds accordingly. Usually, four breaths per respiration cycle is the standard. Exhalation relates to the Heart and Lung; inhalation relates to the Kidney and Liver. The Stomach governs all four directions during respiration. Rapid indicates Heat; slow indicates Cold. Like the equinoxes of Spring and Autumn, dividing Yin and Yang, balancing day and night, each obtaining fifty degrees. Adding one degree brings Heat; subtracting one brings Cold. The subtlety of the pulse can be understood from this. It may resemble scattered leaves, burning firewood, clay balls, silk threads, gushing springs, vomiting debris, an inverted knife, turning ropes, or swimming fish. If it undergoes thousands of changes and becomes abnormal, it signifies the severance of True Primordial Qi. The Classics state: "Accumulated Yang becomes Heaven; accumulated Yin becomes Earth. Yang transforms into Qi; Yin forms shape." This speaks of the separation of One Qi into clear and turbid. Primordial Qi is the root of Heaven and Earth. Hua Tuo said: "The Mai is the precursor of Qi and Blood." Confucius said: "Heaven does not speak, yet the four seasons proceed, and all things are born." The pulse is likewise. Another Classic states: "Since ancient times, those who connect with Heaven are the root of life, all connecting with Heavenly Qi." Connecting with Heaven means connecting with True Primordial Qi. The physical body is generated by borrowing Qi from Heaven and Earth; thus, the nurturing Qi connects to Heaven, receiving Yin and Yang as its foundation. Heaven and Earth combine Qi, and this is called Man. Heavenly Qi never ceases; true spirituality is internally attached; movement and change all communicate with Heaven. The *I Ching* states: "When Qian and Kun are arranged, Yi (Change) stands within them." Thus, the body of Heaven and Earth is born through Yi, and its transformation is completed through Yi. When Yang operates, Spring births and Summer grows; when Yin operates, Autumn harvests and Winter stores. Cold goes, Heat comes; Heat goes, Cold comes. Beginning ends it, ending restarts it; this is the transformation of Heaven and Earth. Yi remains silent within, allowing the four seasons to succeed according to their time. Cold does not overwhelm Heat, Heat does not deprive Cold; there are no aberrations of excessive Yang or hidden Yin, avoiding extreme cold or heat. Thus, all things obtain harmonious Qi, acting moderately without excess. The *Dao De Jing* states: "All things carry Yin and embrace Yang, blending Qi to achieve harmony. People use it daily without knowing it." This is the Way of the Mai. Therefore, the Mai cannot be solely floating, sinking, large, small, abundant, deficient, Yin, or Yang. It must contain sinking within floating, floating within sinking, large within small, small within large, abundant within deficient, deficient within abundant, Yin within Yang, and Yang within Yin. It fills the body, overflowing within all bones. No meridian lacks it, no Qi or Blood fails to reach it. It nourishes sinews, bones, hair, and skin, making them firm, strong, smooth, and lustrous. It is not the Heart, nor Kidney, nor Liver, nor Spleen. When the Five Zang are prosperous, True Qi is dense and protected from pathogens. However, sorrow, worry, hunger, fullness, overwork, rest, wind, rain, cold, heat, great fright, or sudden fear consume and confuse True Qi, separating Qi and Blood, becoming the root of disease. Alas! Among all things, the Five Constants are complete. Why should the Way of the Mai lack the Five Constants? Benevolence (Ren) protects the whole body, filling the Five Zang and nourishing the limbs and bones. Without harmonious Qi, if only the True Zang pulse appears, death occurs. Life implies it is not seen; death implies it appears exclusively. Loving life and fearing death is Ren. Distributing throughout the body, harmonizing Qi and Blood, valuing the head, eyes, ears, and nose, and devaluing the soles, buttocks, and genitals. It ascends and descends, applying everywhere, reaching everywhere; this is Righteousness (Yi). Long people have long pulses; short people have short pulses. Fat people have sinking pulses; thin people have floating pulses. Adults have strong pulses; children have weak pulses. If long people have short pulses, short people have long pulses, fat people have floating pulses, thin people have sinking pulses, adults have weak pulses, and children have strong pulses, such cases are unreasonable and indicate disease. This is Propriety (Li). Appearance in the Cun position indicates upper body disease; in the Guan position, middle body disease; in the Chi position, lower body disease. When the Five Zang are diseased, each has specific locations, and the pulse emerges visibly, not hiding, allowing observation of excess and deficiency to cure the disease. This is Wisdom (Zhi). Spring wiry, Summer surging, Autumn feather-like, Winter stone-like. When Taiyang arrives, the pulse is deep; when Taiyin arrives, the pulse is large and long; when Shaoyin arrives, the pulse is floating; when Yangming arrives, the pulse is rough and short; when Shaoyang arrives, the pulse is hooked; when Jueyin arrives, the pulse is wiry. If the four seasons do not lose their timing, and the Six Qi serve as constant standards, this is Trustworthiness (Xin). Only those who explore profound mysteries, penetrate depth, extend far, integrate learning of Heaven and Humanity, and understand natural principles can reach this understanding.