卫气，阳气也，即人之天气也。天有二十八宿，周布四面，（一面七星，四七二十八星
。）
，主
周于身，与宗气、营气度数相等。或曰∶卫气出于何所？行于何地乎？曰∶宗气积于上焦，营
气出于中焦，而卫气则出于下焦。营气随宗气行于经脉之中，卫气则不随宗气入于经脉，而
自行于各经脉外，及头目、手足、皮肤、分肉之间。故经曰∶清者为营，浊者为卫；营行脉
中，卫行脉外。或又曰∶卫气何以出于下焦，行于脉外乎？曰∶经谓上焦如雾，（此三焦，即
三
谷
下
正以下焦如渎之畜泄乎水也。）卫气赖下焦阴中真阳，以升出中、上二焦，故卫气出于下焦
。营为水谷之精气，属阴，阴性精专，自行脉中；卫为水谷之悍气，属阳，阳性剽悍滑利，
故行脉外。
请析言之。平旦阴尽，由寐而寤。邵子曰∶人之神，寐则栖肾，寤则栖心，将寐在脾，
熟寐在肾，将寤在肝，正寤在心。十二经脉，皆根于心。寤属阳，太阳为阳中之阳，故经曰
∶人寤则目张。目张则阳气出于睛明穴（属足太阳经），而上行于头，始于足太阳，次手太
阳，
而寐。目合则阳气从足少阴注于肾，肾注于心，心注于肺，肺注于肝，肝注于脾，脾复注于
肾，如是亦周二十五度，终而复始，如环无端。
再析言之。如卯初初刻，阴尽而寤，卫行太阳；（先行足经，次行手经。余皆同。）卯初
一
卯正一刻，卫复行少阳；卯正二刻，卫复行阳明；卯正三刻，卫复间行足少阴。阳尽间阴者
，以足少阴阴阳互根，为人身之大根柢、大枢纽也。如是环行，自卯至申，周二十五度，阳
尽于阴，阴受气矣，阴亦周二十五度。一昼一夜，漏下百刻而尽，卫气五十度周于身，如是
无已，与天地同纪。知此，则人之病否、生死可以决，药之升降、补泻、表里、阴阳可无差
矣。
卫气，属于阳气，也就是人体与自然界相通的天之气。天有二十八宿，均匀分布在四方，（每方七星，四七共二十八星），卫气在人体内循环运行，其运行的度数与宗气、营气相等。有人问：卫气产生于何处？运行于何地呢？回答说：宗气积聚在上焦，营气产生于中焦，而卫气则产生于下焦。营气跟随宗气在经脉内部运行，卫气却不跟随宗气进入经脉，而是自行运行在各经脉外部，以及头目、手足、皮肤、肌肉间隙之间。所以《内经》说：清轻的部分化为营气，重浊的部分化为卫气；营气行于脉中，卫气行于脉外。又有人问：卫气为什么产生于下焦，运行于脉外呢？回答说：经典说上焦如雾（这里提到的三焦，即指下焦像沟渠一样蓄积和排泄水液的功能），卫气依赖下焦阴中的真阳之气，升发而出到达中、上二焦，所以说卫气出于下焦。营气是水谷的精微之气，属于阴，阴性精纯专一，所以自行于脉中；卫气是水谷的悍烈之气，属于阳，阳性剽悍滑利，所以行于脉外。
请详细分析其道理。清晨时分，阴气尽而阳气生，人从睡眠中醒来。邵子说：人的神志，睡觉时栖息于肾，清醒时栖息于心，将睡时在脾，熟睡时在肾，将醒时在肝，正醒时在心。十二经脉，都根源于心。清醒属于阳，太阳经为阳中之阳，所以《内经》说：人清醒时眼睛睁开。眼睛睁开，则阳气出于睛明穴（属足太阳膀胱经），向上运行至头部，起始于足太阳经，接着是手太阳经，然后入睡。眼睛闭合，则阳气从足少阴肾经注入肾脏，肾注于心，心注于肺，肺注于肝，肝注于脾，脾再注回肾，这样也循环二十五周，终而复始，如环无端。
再详细分析。如在卯初初刻，阴气尽而人醒，卫气运行于太阳经；（先运行足部经脉，后运行手部经脉。其余情况相同。）卯初一刻，卫气再次运行于少阳经；卯正二刻，卫气再次运行于阳明经；卯正三刻，卫气再次间歇性地运行于足少阴经。阳气尽而间歇运行阴经的原因，是因为足少阴肾经阴阳互根，是人体最大的根基和枢纽。这样循环运行，从卯时至申时，循环二十五周，阳气尽而转入阴分，阴分接受气机了，阴分也循环二十五周。一昼一夜，漏壶滴水一百刻结束，卫气在体内五十周循环，如此不停息，与天地运行的规律同步。懂得这个道理，那么人的疾病与否、生死就可以判断，药物的升降、补泻、表里、阴阳运用就不会出差错了。
Wei Qi (Defensive Qi), which is a form of Yang Qi, corresponds to the Heavenly Qi in humans. The heavens have Twenty-Eight Mansions (the lunar lodgings), distributed evenly around the four directions (seven stars per direction, totaling twenty-eight stars). Wei Qi circulates throughout the body, and its rhythmic cycles are equal in measure to those of Zong Qi (Pectoral Qi) and Ying Qi (Nutritive Qi). Some ask: From where does Wei Qi originate? Where does it travel? The answer is: Zong Qi accumulates in the Upper Jiao (Upper Burner), Ying Qi originates from the Middle Jiao (Middle Burner), while Wei Qi originates from the Lower Jiao (Lower Burner). Ying Qi follows Zong Qi within the meridians, whereas Wei Qi does not enter the meridians with Zong Qi but travels independently outside the various meridians, as well as in the head, eyes, hands, feet, skin, and between the muscles. Thus, the Classics state: The clear and light part becomes Ying Qi, the turbid and heavy part becomes Wei Qi; Ying Qi travels within the vessels, Wei Qi travels outside the vessels. Others ask: Why does Wei Qi originate from the Lower Jiao and travel outside the vessels? The answer is: The Classics describe the Upper Jiao as like a mist (referring to the function of the San Jiao, specifically how the Lower Jiao acts like a ditch to store and drain fluids). Wei Qi relies on the True Yang within the Yin of the Lower Jiao to ascend and emerge into the Middle and Upper Jiao; therefore, it is said that Wei Qi originates from the Lower Jiao. Ying Qi is the essence of water and grain, belonging to Yin; its nature is pure and specialized, so it travels within the vessels. Wei Qi is the fierce Qi of water and grain, belonging to Yang; its nature is bold, swift, and slippery, so it travels outside the vessels.
Let us analyze this in detail. At dawn, when Yin is exhausted and Yang arises, one wakes from sleep. Shao Zi stated: The human spirit resides in the Kidney during sleep, in the Heart during wakefulness, in the Spleen when about to sleep, in the Kidney during deep sleep, in the Liver when about to wake, and in the Heart when fully awake. The Twelve Meridians all root in the Heart. Wakefulness belongs to Yang; the Taiyang (Greater Yang) meridian is Yang within Yang. Therefore, the Classics say: When a person is awake, their eyes open. When the eyes open, Yang Qi emerges from Jingming (BL1, Foot-Taiyang Bladder Meridian) and travels upward to the head, starting with the Foot-Taiyang, then the Hand-Taiyang, until sleep occurs. When the eyes close, Yang Qi flows 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. This also completes twenty-five cycles, ending and beginning again, like a circle without end.
Let us analyze further. At the first quarter of Mao (5:00-5:15 AM), when Yin is exhausted and one wakes, Wei Qi travels through the Taiyang meridian; (it first travels the Foot meridians, then the Hand meridians. The same applies to others.) At the second quarter of Mao, Wei Qi travels through the Shaoyang (Lesser Yang) meridian; at the third quarter of Mao, Wei Qi travels through the Yangming (Bright Yang) meridian; at the fourth quarter of Mao, Wei Qi intermittently travels through the Foot-Shaoyin meridian. The reason for Yang exhausting and intermittently traveling through Yin meridians is that the Foot-Shaoyin (Kidney) meridian has Yin and Yang rooted in each other, serving as the great foundation and pivot of the human body. Circulating in this manner, from Mao to Shen (5:00 AM to 3:00 PM), it completes twenty-five cycles. Yang exhausts into Yin, and Yin receives the Qi; Yin also completes twenty-five cycles. In one day and night, as the clepsydra (water clock) drains one hundred quarters, Wei Qi completes fifty cycles throughout the body, ceaselessly continuing, synchronized with the rhythms of Heaven and Earth. Understanding this, one can determine whether a person is ill or healthy, alive or dead, and the administration of herbs—regarding ascending/descending, tonifying/reducing, exterior/interior, and Yin/Yang—will be free from error.