夫子午流注者，刚柔相配，阴阳相合，气血循环，时穴开阖也。何以子午言之？曰∶子
时一
者，住也。天干有十，经有十二，甲胆、乙肝、丙小肠、丁心、戊胃、己脾、庚大肠、辛肺
、壬膀胱、癸肾，余两经者，乃三焦、包络也。三焦乃阳气之父，包络乃阴血之母。此二经
虽寄于壬癸，亦分派于十干。且每经之中，有井荥俞经合，以配金水木火土。是故阴井木而
阳井金，阴荥火而阳荥水，阴俞土而阳俞木，阴经金而阳经火，阴合水而阳合土矣。经中必
有返本还原者，乃十二经出入之门户也。阳经有原，遇俞穴并过之，阴经无原，以俞穴即代
之。是以甲出丘墟乙太冲之例。又按《千金》云∶六阴经亦有原穴，乙中都、丁通里、己公
孙、辛列缺、癸水泉，包络内关也。故阳日气先行而血后随也，阴日血先行而气后随也。得
时为之开，失时为之阖。阳干注腑，甲丙戊庚壬而重见者，气纳于三焦。阴干注脏，乙丁己
辛癸而重见者，血纳包络。如甲日戌时，以开胆井，至戊寅时，正当胃俞，而又并过胆原，
重见甲申时，气纳三焦荥穴，属水，甲属木，是以水生木，谓甲合还元化本。又如乙日乙酉时，
以开肝井，至己丑时，当脾之俞，并过肝原，重见乙未时，血纳包络荥穴，属火
，乙属木，是以木生火也。余皆根据此。俱以子午相生，阴阳相济也。阳日无阴时，阴日无阳
时。故甲与己合，乙与庚合，丙与辛合，丁与壬合，戊与癸合也。何以甲与己合？曰∶中央
戊己属土，畏东方甲乙之木所克，戊属阳为兄，己属阴为妹，戊兄遂将己妹嫁与木家，与甲
为妻，庶得阴阳和合而不相伤。所以甲与己合，余皆然。子午之法，尽于此矣。
The method of Zi Wu Liu Zhu (Midnight-Noon Ebb-Flow) refers to the matching of rigidity and softness between Heavenly Stems and Earthly Branches, the harmony of Yin and Yang, the circulation of Qi and Blood in meridians, and the opening and closing of specific acupoints according to time. Why is it named after "Zi" (Rat hour/Midnight) and "Wu" (Horse hour/Noon)? The answer is: "Zi" here means "to stay" or "to reside."
There are ten Heavenly Stems and twelve Meridians. Among them, Jia corresponds to the Gallbladder Meridian, Yi to the Liver Meridian, Bing to the Small Intestine Meridian, Ding to the Heart Meridian, Wu to the Stomach Meridian, Ji to the Spleen Meridian, Geng to the Large Intestine Meridian, Xin to the Lung Meridian, Ren to the Bladder Meridian, and Gui to the Kidney Meridian. The remaining two meridians are the Sanjiao (Triple Burner) Meridian and the Pericardium Meridian. The Sanjiao is the father of Yang Qi, and the Pericardium is the mother of Yin Blood. Although these two meridians are attached under the stems Ren and Gui, they are also distributed among the ten Heavenly Stems.
Furthermore, within each meridian, there are five Shu points—Jing-Well, Ying-Spring, Shu-Stream, Jing-River, and He-Sea—which correspond to the Five Elements: Metal, Water, Wood, Fire, and Earth. Thus, the Jing-Well point of Yin meridians belongs to Wood, while that of Yang meridals belongs to Metal; the Ying-Spring of Yin belongs to Fire, while that of Yang belongs to Water; the Shu-Stream of Yin belongs to Earth, while that of Yang belongs to Wood; the Jing-River of Yin belongs to Metal, while that of Yang belongs to Fire; and the He-Sea of Yin belongs to Water, while that of Yang belongs to Earth.
In the flow through meridians, there must be a step of "returning to the origin," which serves as the gateway for the entry and exit of the twelve meridians. Yang meridians have Yuan-Source points; when the flow passes the Shu-Stream point, it simultaneously passes the Yuan-Source point. Yin meridians do not have independent Yuan-Source points, so their Shu-Stream points serve as Yuan-Source points. This is the example of why Jia (Gallbladder) flows out from Qiuxu (GB40, Gallbladder Yuan-Source) and Yi (Liver) flows from Taichong (LR3, Liver Yuan-Source/Shu-Stream).
Additionally, according to *Qianjin Fang* (Essential Prescriptions Worth a Thousand Gold), the six Yin meridians also have Yuan-Source points: Zhongdu (LR6) for Yi, Tongli (HT5) for Ding, Gongson (SP4) for Ji, Lieque (LU7) for Xin, Shuiquan (KI5) for Gui, and Neiguan (PC6) for the Pericardium. Therefore, on Yang days, Qi moves first and Blood follows later; on Yin days, Blood moves first and Qi follows later. When the time is right, the points open; when the time is missed, the points close.
Yang stems (Jia, Bing, Wu, Geng, Ren) flow into the Fu organs. If a stem repeats (reappears), the Qi is absorbed by the Sanjiao Meridian. Yin stems (Yi, Ding, Ji, Xin, Gui) flow into the Zang organs. If a stem repeats, the Blood is absorbed by the Pericardium Meridian. For example, on a Jia day at Xu hour, the Jing-Well point of the Gallbladder is opened. By Wu Yin hour, it reaches the Shu-Stream point of the Stomach, simultaneously passing the Yuan-Source point of the Gallbladder. Upon encountering Jia Shen hour again, the Qi is absorbed by the Ying-Spring point of the Sanjiao, which belongs to Water. Since Jia belongs to Wood, this represents Water generating Wood, termed "Jia combines and returns to its origin to transform its essence." Similarly, on a Yi day at Yi You hour, the Jing-Well point of the Liver is opened. By Ji Chou hour, it reaches the Shu-Stream point of the Spleen, simultaneously passing the Yuan-Source point of the Liver. Upon encountering Yi Wei hour again, the Blood is absorbed by the Ying-Spring point of the Pericardium, which belongs to Fire. Since Yi belongs to Wood, this represents Wood generating Fire. All other cases follow this principle. This is all based on the generation of Zi and Wu and the mutual complementarity of Yin and Yang. Yang days have no Yin hours, and Yin days have no Yang hours. Therefore, Jia combines with Ji, Yi with Geng, Bing with Xin, Ding with Ren, and Wu with Gui.
Why do Jia and Ji combine? The answer is: Central Wu and Ji belong to Earth, which fears being controlled by the Wood of Eastern Jia and Yi. Wu is Yang and acts as the elder brother; Ji is Yin and acts as the younger sister. The elder brother Wu marries off his sister Ji to the Wood family, making her the wife of Jia, thereby achieving harmony between Yin and Yang without mutual harm. Thus, Jia combines with Ji, and the rest follow similarly. The principles of Zi Wu Liu Zhu end here.