六十四难曰∶《十变》又言∶阴井木，阳井金；阴荥火，阳荥水；阴输土，阳输木；阴经
金，阳经火；阴合水，阳合土。
人身经脉，起于井穴，五脏属阴，从春夏而至秋冬，故阴井为木。阴井木生阴荥火，阴荥火
生阴输土，阴输土生阴经金，阴经金生阴合水。六腑属阳，从秋冬而至春夏，故阳井为金，阳
井金生阳荥水，阳荥水生阳输木，阳输木生阳经火，阳经火生阳合土。此阴阳逆顺之气，五行
相生之序也。
阴阳皆不同，其意何也？
然∶是刚柔之事也。阴井乙木，阳井庚金。阳井庚，庚者，乙之刚也；
阴井乙，乙者，庚之柔也。乙为木，故言阴井木也；庚为金，故言阳井金也。余皆仿此。
刚柔者，即乙庚之配合也。阴井为木，乙，阴木也。阳井为金，庚，阳金也。乙与庚合，以阴
木合阳金，故曰庚乃乙之刚，乙乃庚之柔也。阴荥火，阳荥水，是丁与壬合也。阳输木，阴输
土，是甲与己合也。阳经火，阴经金，是丙与辛合也。阳合土，阴合水，是戊与癸合也。此阴
阳配合之道也。其十干化合之义，已详三十三难中，当参互观之。
按∶《灵枢·本输篇》论井荥输经合甚详，欲求脏腑经脉之血气生死出入者，不可不知也。
其义以营卫气血，皆生于胃腑水谷之精，营行脉中，卫行脉外，血行脉中，气行脉外。然血中
有气，气中有血，阴阳互根，不可相离。是脉内之血气，从气卫而渗灌于脉外，脉外之气血，
亦从孙络而溜注于络中，外内出入之相通也。五脏内合五行，故其俞五，六腑外合六气，故其俞
六。盖六气生于五行，而有二火也。人身十二经脉，合六脏六腑之十二大络，及督脉之长强，
任脉之尾翳，脾之大包，凡二十七脉之血气，出入于手足指之间，所出为井，所溜为荥，所注
为输，所行为经，所入为合。此二十七脉之血气，从四肢通于脏腑，而脏腑中之血气，又从经
脉缪处通于孙络，而溜于络脉，交相逆顺而行，外而皮肤，内而经脉者也。夫经脉有三百六十
五穴会，络脉有三百六十五穴会，孙络亦有三百六十五穴会，经脉宽大，孙络窄小，经脉深而
络脉浅，故黄帝有五脏之所溜处，阔散之度，浅深之状，高下所至之问也。而医言过心化赤之
血，由脉管行遍，散诸微丝管，由微丝管之尾，渐并渐粗，入回血管，血入回血管，其色变紫，
与脉管交相逆顺而行，至总回管，过心入肺，呼出炭气，吸入养气，复化为赤血者，即此义也。
西医知血之行诸脉络，而不知所以能行者，气为之也。其井荥输经合五行出入之道，西医昧而
不明，是知其所当然，而不知其所以然也。
The Sixty-fourth Difficulty states: The "Shi Bian" (Ten Transformations) further mentions: Yin Jing (Well) points belong to Wood, Yang Jing (Well) points belong to Metal; Yin Ying (Spring) points belong to Fire, Yang Ying (Spring) points belong to Water; Yin Shu (Stream) points belong to Earth, Yang Shu (Stream) points belong to Wood; Yin Jing (River) points belong to Metal, Yang Jing (River) points belong to Fire; Yin He (Sea) points belong to Water, Yang He (Sea) points belong to Earth.
Human meridians originate at the Jing-Well points. The Zang organs belong to Yin and follow the progression from Spring/Summer to Autumn/Winter; therefore, Yin Jing-Well points belong to Wood. Yin Jing-Well (Wood) generates Yin Ying-Spring (Fire); Yin Ying-Spring (Fire) generates Yin Shu-Stream (Earth); Yin Shu-Stream (Earth) generates Yin Jing-River (Metal); Yin Jing-River (Metal) generates Yin He-Sea (Water). The Fu organs belong to Yang and follow the progression from Autumn/Winter to Spring/Summer; therefore, Yang Jing-Well points belong to Metal, Yang Jing-Well (Metal) generates Yang Ying-Spring (Water); Yang Ying-Spring (Water) generates Yang Shu-Stream (Wood); Yang Shu-Stream (Wood) generates Yang Jing-River (Fire); Yang Jing-River (Fire) generates Yang He-Sea (Earth). This represents the Qi dynamics of Yin-Yang reversal and sequence, as well as the order of the Five Elements generating each other.
Since Yin and Yang [attributes of the Five Shu points] are different, what is the meaning behind this?
It is answered: This concerns the matter of Gang (Firm/Hard) and Rou (Soft/Yielding). Yin Jing-Well corresponds to Yi Wood, and Yang Jing-Well corresponds to Geng Metal. In Yang Jing-Well, Geng is the Gang of Yi; in Yin Jing-Well, Yi is the Rou of Geng. Since Yi belongs to Wood, it is said that Yin Jing-Well belongs to Wood; since Geng belongs to Metal, it is said that Yang Jing-Well belongs to Metal. The rest follow this pattern.
Gang and Rou refer to the pairing of Yi and Geng. Yin Jing-Well is Wood; Yi is Yin Wood. Yang Jing-Well is Metal; Geng is Yang Metal. Yi and Geng combine; combining Yin Wood with Yang Metal, it is said that Geng is the Gang of Yi, and Yi is the Rou of Geng. Yin Ying-Spring is Fire, Yang Ying-Spring is Water; this is the combination of Ding and Ren. Yang Shu-Stream is Wood, Yin Shu-Stream is Earth; this is the combination of Jia and Ji. Yang Jing-River is Fire, Yin Jing-River is Metal; this is the combination of Bing and Xin. Yang He-Sea is Earth, Yin He-Sea is Water; this is the combination of Wu and Gui. This is the way of Yin-Yang combination. The meaning of the ten Heavenly Stems' combinations has been detailed in the Thirty-third Difficulty; one should consult it for cross-reference.
Note: The "Ben Shu" chapter of the *Ling Shu* discusses the Jing-Well, Ying-Spring, Shu-Stream, Jing-River, and He-Sea points in great detail. Those who seek to understand the life, death, entry, and exit of Blood and Qi in the Zang-Fu organs and meridians must not be ignorant of these principles.
The principle lies in the fact that Ying-Qi, Wei-Qi, Blood, and Qi all originate from the essence of water and grain digested by the Stomach. Ying-Qi circulates within the vessels, while Wei-Qi circulates outside the vessels; Blood circulates within the vessels, while Qi circulates outside the vessels. However, there is Qi within Blood, and Blood within Qi; Yin and Yang are mutually rooted and cannot be separated. Thus, the Blood and Qi within the vessels permeate and irrigate outside the vessels via the Wei-Qi, and the Qi and Blood outside the vessels flow into the Luo vessels via the Sun-Luo vessels. This demonstrates the mutual connection of internal and external entry and exit.
The five Zang organs internally correspond to the Five Elements, hence their Shu points number five. The six Fu organs externally correspond to the Six Qi, hence their Shu points number six. Generally, the Six Qi arise from the Five Elements, but include two Fires. The twelve meridians of the human body correspond to the twelve major Luo vessels of the six Zang and six Fu organs, as well as Changqiang (GV1) of the Du vessel, Weiyi (CV15) of the Ren vessel, and Dabao (SP21) of the Spleen, totaling twenty-seven vessels. The Blood and Qi of these twenty-seven vessels enter and exit between the fingers and toes. What emerges is called the Jing-Well point; what trickles is called the Ying-Spring point; what pours is called the Shu-Stream point; what flows is called the Jing-River point; what enters is called the He-Sea point. The Blood and Qi of these twenty-seven vessels travel from the limbs to the Zang-Fu organs, and the Blood and Qi within the Zang-Fu organs travel from the intersections of the meridians to the Sun-Luo vessels, then flow into the Luo vessels. They move in alternating reverse and forward directions, extending outward to the skin and inward to the meridians.
There are three hundred and sixty-five intersection points for the main meridians, three hundred and sixty-five for the Luo vessels, and three hundred and sixty-five for the Sun-Luo vessels. The main meridians are broad, while the Sun-Luo vessels are narrow; the main meridians are deep, while the Luo vessels are superficial. Therefore, the Yellow Emperor asked about the places where the Qi of the five Zang organs trickles, the degree of its breadth and dispersion, its depth and superficiality, and the extent of its reach.
Physicians speak of blood that turns red after passing through the heart, which travels through the vascular tubes, disperses into various capillaries, and gradually merges and thickens from the ends of the capillaries into venous vessels. When blood enters the venous vessels, its color changes to purple. It moves in alternating reverse and forward directions relative to arterial blood, reaches the vena cava, passes through the heart into the lungs, exhales carbon dioxide, inhales oxygen, and is reconverted into red blood. This process embodies the meaning described above.
Western medicine knows that blood circulates through the vessels but does not know the reason why it can circulate, which is due to the action of Qi. Regarding the pathways of entry and exit of the Five Elements in the Jing-Well, Ying-Spring, Shu-Stream, Jing-River, and He-Sea points, Western medicine is vague and unclear. This means they know what happens (the phenomenon) but do not know why it happens (the underlying mechanism).