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The *Ling Shu* states that there is Yin and Yang internally, and also externally. Internally, the Five Zang Organs are Yin, and the Six Fu Organs are Yang. Externally, the sinews and bones are Yin, and the skin and hair are Yang (from the chapter "Shou Yao Gang Rou"). The *Su Wen* states: Yang channels receive Wind pathogenic factors, while Yin channels receive Dampness pathogenic factors. Therefore, Yin Qi ascends from the feet to the head, then descends along the arms to the fingertips; Yang Qi ascends from the hands to the head, then descends to the feet. Thus it is said that diseases of Yang ascend, reaching their peak before descending; diseases of Yin descend, reaching their peak before ascending (this refers to the concept of alternating reversal and compliance, but this merely describes the general principle. If the Foot Taiyin channel descends, it would not be consistent with other Yin channels) (from the chapter "Tai Yang Yang Ming Lun").

Li Dongyuan stated: In cases where symptoms worsen during the day and remain quiet at night, it indicates excess in Yang disease, which is a disorder of Qi without involvement of Blood. In cases where symptoms worsen at night and remain quiet during the day, it indicates excess in Yin disease, which is a disorder of Blood without involvement of Qi. In febrile diseases where fever occurs during the day and quietness at night, it signifies that Yang Qi is flourishing in the Yang aspect. When quiet during the day and feverish with irritability at night, it signifies that Yang Qi has sunk into the Yin, termed "Heat Entering the Blood Chamber" (Re Ru Xue Shi). When fever and irritability persist throughout both day and night, it indicates Extreme Yang with absence of Yin, requiring urgent draining of Yang and vigorous tonification of Yin. In cold diseases, if chills occur at night and quietness during the day, it signifies that Yin Blood is flourishing in the Yin aspect. If quiet at night and chills during the day, it signifies that Yin Qi is overflowing into the Yang aspect. If chills persist throughout both day and night, it indicates Extreme Yin with absence of Yang, requiring urgent draining of Yin and vigorous tonification of Yang. If chills occur during the day, irritability at night, and inability to ingest food, it is termed "Yin-Yang Intertwining," a condition leading to death.

The *Nei Jing* states: The Five Zang Organs store Spirit, Qi, Blood, Hun, and Po; they store but do not drain, thus remaining full but not solid. The Six Fu Organs transform water and grain and transport Body Fluids; they transmit but do not store, thus remaining solid but not full. This is because when food enters the mouth, the Stomach becomes full and the Intestines empty; after food moves down, the Intestines become full and the Stomach empties. (This section summarizes content from the chapters "Ben Cang" of *Ling Shu* and "Wu Zang Bie Lun" of *Su Wen*).

The *Nan Jing* states: Zang organs belong to Yin; Yin diseases desire warmth, prefer closing doors and staying alone, and dislike hearing human voices. Fu organs belong to Yang; Yang diseases desire coolness and prefer seeing people. Thus, one can distinguish diseases of Zang and Fu based on these signs (Yin diseases are cold, hence desiring heat. Yin nature prefers tranquility, hence closing doors and staying alone, disliking noise. Yang diseases are hot, hence desiring coolness. Yang nature prefers activity/disturbance, hence desiring company). Diseases of Zang are static and do not migrate; the pathology remains at its original location. Diseases of Fu resemble rushing sounds, flowing up and down, with no fixed location. (This section summarizes content from Difficulties 51 and 52). It further states: There are twelve meridians. Currently, the Five Zang and Six Fu account for only eleven. The remaining one is the Hand Jueyin Pericardium Channel (The Hand Shaoyin channel is the True Heart channel. The Pericardium channel, named Master of the Heart, is an accessory branch of the True Heart and does not share the same meridian as the True Heart, because the True Heart represents Ministerial Fire, while the Pericardium represents Ministerial Fire [Note: Text implies True Heart is Sovereign Fire/Ministerial distinction contextually, but text says 'Zhen Xin Wei Jun Huo' - True Heart is Sovereign Fire]. The San Jiao is the Father of Qi, and the Pericardium is the Mother of Blood; they are exterior-interior pairs. Both have names but no distinct physical form. Thus, adding the Hand Jueyin Pericardium channel to the Five Zang and Six Fu results in twelve channels). There are five Zang organs, yet six Fu organs, referring to the San Jiao. Its meridian belongs to the Hand Shaoyang, making it an external Fu organ (San Jiao Qi combines with the Kidney; the Kidney is the root of Yuan Qi. San Jiao is the branch of Yuan Qi, governing the Qi of the whole body, having a name but no form). However, there are also six Zang organs, referring to the two Kidneys. The left is the Kidney, and the right is the Gate of Vitality (Ming Men). The Gate of Vitality is the residence of Spirit and Essence; in men, it stores Essence; in women, it anchors the Uterus. Its Qi connects with the Kidney. (This section modifies content from Difficulties 38 and 39).

The *Su Wen* states: The domains governed by the Five Zang Organs: The Heart governs Blood vessels (restraining Ying Qi, moving with each pulse beat); the Lung governs Skin and Hair (wrapping muscles and sinews, repelling various pathogens); the Liver governs Sinews and Membranes (binding and connecting joints, moving with Shen); the Spleen governs Muscles (covering and hiding sinews and bones, transporting Wei Qi); the Kidney governs Marrow (expanding sinews to generate marrow, supporting the body's stance). The aspects stored by the Five Zang Organs: The Heart stores Shen (Spirit) (when two Essences interact, it is called Shen); the Lung stores Po (Corporeal Soul) (that which exits and enters with Essence is called Po); the Liver stores Hun (Ethereal Soul) (that which comes and goes with Shen is called Hun); the Spleen stores Yi (Intellect) (what the mind remembers is called Yi); the Kidney stores Zhi (Will) (what Yi retains is called Zhi. Yang Shangshan stated: The Kidney has two parts; the left Kidney stores Zhi, and the right Gate of Vitality stores Essence). (This section slightly expands content from the chapter "Xuan Ming Wu Qi").