有问于予曰。卫气昼行阳夜行阴。其行皆以传经行度。此义不疑乎。曰。有。轩岐本经本无误诠之文。独于论卫气。
远引宿度。别列其所行之经络。若犹然营气行度者。然于气之剽悍不循经之说不合。而诸家未能洞悉其故。泥以行度为
二十五周。是不可以不辨。盖卫气者。即太阳之盛气。所以卫外而为固。其气则剽悍不循经隧。内薰肓膜。外溢皮毛。
其所出入阴阳皆满。所以名卫。若待以次而行阳行阴。则已有不卫者矣。要其气为纯阳之大气。半入经隧之中以和营。
而半溢经隧之外以为卫。是即所谓体之充也。经衣冠文物言其出下焦。而人言为水谷之悍气。盖谓水谷之气能出卫犹去脉。
得食则高。而要非所以为卫之由也。唯其为下焦先天之本。故能出入阴阳。而无所不至。经曰。平旦阴尽而阳受气。日
入阳尽而阴受气。则常从足少阴入。其于阳目张。则气上行于头。以下六阳。入足心以下阴分。复合于目。于阴则从少
阴内注六阴。是以昼行阳二十五度。夜行阴亦二十五度。此若以经度分之。则卫将为一路之路。抑其未至而不卫者多矣。
故言五十度者。尽昼夜十二时而言也。行阳二十五。极昼六时也。行阴二十五。极夜六时也。平旦阳动而动。即与阳俱
出于目。以下六阳。然非不下阴分也。日入阴静而静。即与少阴同息于诸阴。以遍六阴。然非舍阳而去也。及夜半而大
会于子中者。以肾气动少阳于子。故阴阳相见而会也。总之其气为太阳有余之气。阳明溢满之气。而一本于下焦。故于
太阳阳明之守气外。更有此剽悍以常护于脉外。日得以效用于阳。夜得以效用于阴。其行阳而卫于阳也。如列营然。卒
乘居前。非谓中军无卫也。其行阴而亦为阴之卫也。如宿值然。戒严肘腋。非谓壁垒无军。要其昼夜二十五。各尽六时
言之耳。必若循次而传。何谓之剽气。又何以名卫乎。
A person asked me, "The Wei Qi (Defensive Qi) travels through the Yang aspects during the day and the Yin aspects at night. Its movement follows the sequence of meridians and specific cycles. Is there no doubt about this principle?" I replied, "There is doubt. The original texts of Huangdi and Qibo (the *Neijing*) contain no erroneous explanations. However, in the discussion on Wei Qi, it far-fetchedly references astronomical degrees and separately lists the meridians it traverses, as if it followed a fixed path similar to Ying Qi (Nutritive Qi). This contradicts the description of Wei Qi as swift, fierce, and not confined to the meridian pathways. Furthermore, various schools of thought have failed to thoroughly understand the reason for this, rigidly adhering to the notion that it circulates twenty-five cycles. This requires clarification.
Wei Qi is essentially the abundant Qi of the Taiyang (Greater Yang) channel, responsible for defending the exterior and maintaining solidity. Its nature is swift and fierce, not circulating within the meridian tunnels; internally, it steams the Hui membrane (San Jiao's interior membrane); externally, it overflows into the skin and hair. It fills both Yin and Yang aspects as it enters and exits, hence named 'Wei' (Guard). If it were to wait and move sequentially through the Yang and Yin aspects, parts of the body would remain unguarded. In essence, its nature is pure Yang Grand Qi. Half enters the meridian tunnels to harmonize with Ying Qi, while the other half overflows outside the meridians to serve as defense. This is what is meant by 'the fullness of the form.' The *Neijing* states from the perspective of external attire and cultural symbols that it originates from the Lower Jiao (Lower Burner), while people say it is the fierce Qi derived from food and water. This likely refers to the fact that the Qi of food and water can exit the Wei pathway, becoming elevated upon ingestion, but this is not the fundamental cause of Wei Qi formation. Precisely because it is rooted in the congenital foundation of the Lower Jiao, it can enter and exit Yin and Yang, reaching everywhere. The *Neijing* states: 'At dawn (Pingdan), Yin is exhausted and Yang receives Qi; at sunset, Yang is exhausted and Yin receives Qi.' Thus, it usually enters via the Foot-Shaoyin (Kidney) channel. When one opens their eyes, the Qi moves upward to the head, descends through the six Yang channels, enters the Yin aspect below the sole of the foot, and finally reunites at the eyes. Within the Yin aspect, it enters from Shaoyin and permeates the six Yin channels. Therefore, it travels through the Yang aspect twenty-five times during the day and through the Yin aspect twenty-five times at night. If this were divided strictly by meridian degrees, Wei Qi would follow a single isolated path, leaving many areas unguarded. Hence, the term 'fifty cycles' refers to the entire twelve double-hours of day and night. Traveling through Yang twenty-five times exhausts the six hours of daylight; traveling through Yin twenty-five times exhausts the six hours of nighttime. At dawn, Yang Qi activates, and Wei Qi moves with it, exiting the eyes and descending through the six Yang channels, yet it does not fail to enter the Yin aspect. At sunset, Yin Qi becomes quiet, and Wei Qi rests with the Shaoyin among the various Yin channels, pervading the six Yin channels, yet it does not abandon the Yang aspect. At midnight, they gather in the Zi hour (11 PM - 1 AM); this is because Kidney Qi stimulates Shaoyang Qi at Zi, causing Yin and Yang Qi to meet and converge. In summary, Wei Qi is the surplus Qi of Taiyang and the overflowing Qi of Yangming, fundamentally rooted in the Lower Jiao. Thus, beyond the guarding Qi of Taiyang and Yangming, there is this swift Qi constantly protecting outside the vessels, effective in Yang during the day and in Yin at night. Its movement through Yang to guard Yang is like vanguard troops, with soldiers and cavalry leading the front, implying that the central army also has guards. Its movement through Yin to guard Yin is like sentries on duty, alerting the flanks, implying that the fortifications also hold troops. Ultimately, the twenty-five cycles each for day and night refer to the completion of the respective six-hour periods. If it must follow a sequential transmission, why call it 'swift Qi'? And by what name would it be called 'Wei' (Guard)?"