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According to Zhang Zhongjing's preface: "Although [I] could not cure all diseases, one can see his dedication to various illnesses." Therefore, he divided the exterior-interior and yin-yang of various diseases into six channels (Jing), allowing each to perform its own functions, clarifying the similarities and differences in pulse and symptoms, and distinguishing between cold-heat and deficiency-excess. This enables physicians to treat diseases within the framework of the six channels, employing methods such as sweating (Han), vomiting (Tu), purging (Xia), harmonizing (Hejie), warming (Wen), and tonifying (Bu), without making errors.

Diseases of the whole body are encompassed by the scope of the six channels, just as the *Rites of Zhou* divided official duties into six categories so that hundreds of responsibilities were fulfilled, or as the Heavenly Stems divided into six Qi allowed all things to mature. Cold damage (Shanghan) is merely one type of condition within the six channels. Wang Shuhe did not understand that Zhang Zhongjing's "six channels" referred to geographical boundaries (Jingjie) rather than meridian pathways (Jingluo). He erroneously cited the *Neijing*'s "Treatise on Heat Diseases" (*Rebing Lun*) and wrote a preface for Zhang Zhongjing's book, thereby confusing the therapeutic principles of the six channels. If the principles of the six channels are unclear, then Zhang Zhongjing's methods of differentiating pulses and symptoms will hardly align with the standards for treating all diseases.

The six channels mentioned in the *Neijing* specifically refer to diseases of the meridians, involving only excess heat in the exterior and interior, with no deficiency-cold. Although originating from cold damage, it has transformed into a heat disease; thus, it is called heat disease, not cold damage. It should be known that the heat disease in the *Neijing* is synonymous with warm disease (Wenbing); therefore, there are no aversion-to-cold symptoms, only methods for inducing sweating or purging, with no examples of warming or tonifying. The existence of the chapter "Evaluation of Heat Diseases" (*Ping Rebing Lun*) in the *Neijing* makes this clear.

Wang Shuhe did not investigate the root of diseases but merely analyzed them by name. Thus, the *Neijing* citations in his preface both contradict Zhang Zhongjing's intent and misinterpret Qibo's meaning.

Zhang Zhongjing's six channels divide the body into six regional territories, covering a broad scope. Although using pulses as coordinates, he did not base his theory solely on meridians. Whether wind-cold, wind-heat, internal injury, or external contraction, whether from exterior to interior, cold or heat, deficiency or excess—all are included. Hence, he combined cold damage and miscellaneous diseases into one work, titled *Treatise on Cold Damage and Miscellaneous Diseases*. Consequently, the outlines of the six channels stand independently, unconstrained by meridians, and not fixed by wind-cold.

However, since Zhang Zhongjing stated he used the *Suwen*, he should have expanded upon the broad principles of the six channels in the *Suwen*. According to the "Treatise on Skin Regions" (*Pibu Lun*): "Skin has divisions, vessels have networks; diseases differ, each having specific parts, left/right, upper/lower, locations of yin/yang, and the beginning/end of all meridians." This is the source of Zhang Zhongjing's creation of the six-channel regions. It also states: "Yang governs the exterior, Yin governs the interior." Thus, Zhang Zhongjing assigned the Three Yang to the exterior and the Three Yin to the interior. It further says: "What is in Yang governs entering inward; what is in Yin governs exiting outward, seeping into the interior." Therefore, Zhang Zhongjing associated Yangming with the interior. Shaoyin may present with fever; thus, Zhang Zhongjing uses Fuzi (Aconiti Lateralis Radix Praeparata) in exterior-releasing formulas because of its ability to seep/penetrate. It also states: "Shaoyin's Yin is named Shuru. When entering the meridians, it flows from the Yang aspect into the meridians; when exiting, it flows from the Yin aspect into the bones." Thus, Zhang Zhongjing formulated Mahuang Fuzi Tang (Ephedra and Prepared Aconite Decoction) to treat fever, deep pulse, and absence of interior symptoms, following the principle of flowing from the Yang aspect into the meridians. He formulated Fuzi Tang (Prepared Aconite Decoction) to treat body and joint pain, cold hands and feet, aversion-to-cold on the back, and deep pulse, embodying the principle of flowing from the Yin interior into the bones.

Furthermore, the "Treatise on Separation and Union of Yin and Yang" states: "Taiyang is Kai (Opening)," so Zhang Zhongjing uses it to govern exterior syndromes, taking floating pulse, aversion-to-cold, and stiffness/pain of the head and neck as the outline. His wording resembles the *Rebing Lun*, but his intent differs. "Yangming is He (Closing)," so he uses it to govern interior syndromes, taking stomach excess (Wei Shi) as the outline. Although eye pain and nasal dryness exist, they are not the primary focus. "Shaoyang is Shu (Pivot)," and "Shaoyin is also Shu," so both belong to half-exterior/half-interior syndromes. Shaoyang is the Yang Pivot, focusing on the half-exterior, so bitter taste, dry throat, and vertigo are the outline, excluding chest/flank pain/stiffness. Shaoyin is the Yin Pivot; lethargy or insomnia, desire to vomit but unable, are also half-exterior/half-interior syndromes. Although dry tongue and mouth exist, they are not in the outline, focusing instead on the half-interior.

Does Yangming alone govern the interior? No, all Three Yin govern the interior, but due to different yin-yang positions, their focuses differ. Yangming governs the Yang aspect of interior syndromes; the Yang path is solid, so stomach excess belongs to Yangming. Taiyin governs the Yin aspect of interior syndromes; the Yin path is deficient, so spontaneous diarrhea belongs to Taiyin. Taiyin is Kai and the most Yin within Yin, so it governs interior cold and spontaneous diarrhea. Jueyin is He and Yang within Yin, so it governs interior heat and rebellious Qi. Shaoyin is the pivot within Yin, so its governance varies—sometimes cold, sometimes heat, sometimes exterior, sometimes interior, without fixed rules, similar to Shaoyang.

Let us use geography as an analogy: The six channels are like states. Above the waist is the territory of the Three Yang, governing the exterior based on the surface. The Heart is the borderland of the Three Yang: internally from the chest/heart, externally from the vertex, anteriorly to the head, posteriorly to the shoulders/back, inferiorly to the feet, internally connecting to the Bladder. This is the Taiyang territory. This channel governs Ying and Wei, managing exterior syndromes of the body, like a border state defending against enemies. Internally from the chest/heart to the stomach/intestines, externally from the forehead/skull (like face to abdomen), inferiorly to the feet, this is the Yangming territory. From the heart to the pharynx, retreating to the cheekbones, ascending to eyes/ears, diagonally to the vertex, externally from the flanks, internally belonging to the Gallbladder, this is the Shaoyang territory. Closer than Taiyang, Yangming is like the capital region.

Below the waist is the territory of the Three Yin, governing the interior, not extending to the exterior, as the abdomen is the borderland of the Three Yin. From the abdomen via the Spleen to the intestines and anus, this is the Taiyin territory. From the abdomen to the kidneys and bladder/urethra, this is the Shaoyin territory. From the abdomen via the Liver, ascending through the diaphragm to the heart, along the flanks, descending to the lower abdomen and sinews, this is the Jueyin territory. This channel circulates through the Sanjiao, governing interior syndromes of the body, like a state assisting the capital.

Taiyin and Yangming share the same location but have different treatments, akin to the division of governance by Duke Zhou and Duke Shao. The four channels' locations differ in interior/exterior entry-exit and upper/lower traction, like the ancient kings dividing land and people, interlocking like dog's teeth. If referring to meridians as Jing, these are the roads of the six channels, not the territories. The Zheng (regular), Ke (invading), Hebing (combined), Bingbing (concurrent) pathogens, or those belonging to Spleen/Stomach, are like bandits filling the land—in their own territory, neighboring states, or the capital.

Taiyang territory is largest, adjacent to Shaoyin internally and Yangming externally, so diseases relate. For example, difficulty urinating is originally a Bladder channel disease; Shaoyin disease also presents with difficulty urinating, indicating the pathogen has reached the boundary of Shaoyin. Constipation for 6-7 days, headache, and fever indicate Yangming heat invading Taiyang's boundary. The head and neck are the thoroughfares of Taiyang. Since Taiyang governs Ying and Wei, and the chest/heart is the root of Ying and Wei, which circulate endlessly, it is like border officials and soldiers constantly traveling to the capital. Wheezing and chest fullness indicate Taiyang exterior pathogens entering Yangming territory and causing disturbance, hence called Taiyang-Yangming Combined Disease. If no headache or neck stiffness, but chest oppression/stiffness, rising Qi, and inability to breathe through the throat, this pathogen did not come from Taiyang but is Yangming heat-solid binding in the chest, like rebels causing trouble in their own territory.

The Heart is the master of the six channels, so all six channels can present with vexation. If no head/neck stiffness, vexation does not belong to Taiyang; if no alternating chills/fever, vexation does not belong to Shaoyang; if no Three Yang symptoms, vexation does not belong to the Three Yang. Thus, mental restlessness, palpitations, and inner embarrassment—all deficiency vexations—belong to Yangming, because the Heart resides in the Yangming territory. Yangming is like the capital, so both Heart and Abdomen are within its domain. Pathogen in the Heart causes deficiency vexation; in the Abdomen, excess heat. The Heart is Yang and formless; the Abdomen is Yin and formed.

Diseases of the human body often involve the Heart and Abdomen. Yang pathogens gather in the Heart; Yin pathogens gather in the Abdomen. The Liver is Yang within Yin, so it can cause Yin pathogenic Qi to strike the Heart. Yangming governs interior Yang, so it can cause Yang pathogens to gather in the Abdomen.

Again, let us use military strategy as an analogy. The essence of strategy is knowing terrain and where bandits come from. Knowing which direction leads to which prefecture. The incoming route is the border pass (Three Yang); the outgoing route is the interior (Three Yin). The six channels' incoming routes differ: Taiyang is the main road, Shaoyin is the remote path, Yangming is the direct road, Taiyin is the nearby road, Shaoyin is the rear road, Jueyin is the diagonal road. Invading pathogens mostly come from the Three Yang; regular pathogens often arise from the Three Yin, like foreign invaders coming from borders or rebels arising from the interior.

Understanding the terrain of the six channels allows one to grasp the pivot of all diseases; detailing the incoming routes allows one to control the rules of treatment. By symptom: Cold damage is a major invader, disease from outside; Wind strike is a roaming bandit, disease spreading from sides; Miscellaneous disease is a rebel, disease arising from within. Once identified as a certain type of bandit and known origin, defend at the source. If disaster spreads to neighboring counties, attack from two sides. If pathogen enters Taiyang territory, release via sweating, like deploying troops at key points and striking before they settle. Light pathogens are in the Wei (Defensive) level; heavy in the Ying (Nutritive) level; especially heavy in the chest/diaphragm, like bandits shallow outside the pass, deep at the pass, deepest inside. Thus, Mahuang (Ephedrae Herba) represents troops outside the pass; Guizhi (Cinnamomi Ramulus) and Gegen (Puerariae Lobatae Radix) represent troops at the pass; Da Qinglong Tang (Major Blue-Green Dragon Decoction) and Xiao Qinglong Tang (Minor Blue-Green Dragon Decoction) represent troops inside the pass.

When external invaders are unstable, internal thieves rise in response, hence the method of dual resolution, leading to formulas like Da/Xiao Qinglong Tang and modified Guizhi/Mahuang formulas. If the vanguard lacks discipline causing internal chaos, prioritize interior over exterior, hence Wuling San (Five-Ling Powder), Shizao Tang (Ten-Jujube Decoction), Xianxiong Tang (Trap-Chest Decoction), Xiexin Tang (Drain-Epigastric Decoction), Didang Tang (Eliminate-Accumulation Decoction).

If pathogen enters Shaoyang territory, mix exterior/interior, cold/heat, attacking/tonifying agents for defense and resolution. Like narrow paths favoring short weapons over spears, and defense over offense. Light pathogens enter Couli (pores); heavy enter Muyuan (fascial spaces); especially heavy enter Spleen/Stomach. Xiao Chaihu Tang (Minor Bupleurum Decoction) treats Couli; Da Chaihu Tang (Major Bupleurum Decoction) treats Muyuan; Xiao Jianzhong Tang (Minor Construct the Middle Decoction), Banxia Xiexin Tang (Pinellia Drain Epigastric Decoction), Huangqin (Scutellariae Radix), Huanglian (Coptidis Rhizoma) are Shaoyang Spleen agents; Chaihu Jia Mangxiao Tang (Bupleurum Plus Gypsum Decoction) and Chaihu Jia Muli Tang (Bupleurum Plus Oyster Shell Decoction) are Shaoyang Stomach agents. If Taiyang-Shaoyang Combined/Concurrent disease occurs, it is one army invading Shaoyang; Chaihu Guizhi Tang (Bupleurum and Cinnamon Twig Decoction) is a two-pronged attack. If all Three Yang combine, it is three-sided enemy attack; the method is to isolate Yangming. If Yangming territory is secured, Yang pathogens from Taiyang/Shaoyang resolve spontaneously. If internal rebels calm, external invaders cease; this is why Baihu Tang (White Tiger Decoction) succeeds.

If Yang pathogens do not fight in the interior, use Dachengqi Tang (Major Order the Qi Decoction) for urgent purging, attacking bandits to protect the lord. If Yin pathogens directly invade the Central Palace, use Sini Tang (Frigid Extremities Decoction) to urgently rescue the interior, strengthening the lord to expel bandits. Yangming is the interior, with Yang facing the border (Taiyang/Shaoyang). If pathogen enters Yangming near Taiyang, though not invading Taiyang, Taiyang troops cannot ignore it; thus, Yangming Ying/Wei diseases borrow Mahuang-type formulas for sweating. Near Shaoyang, though not entering Shaoyang, Shaoyang troops cannot remain passive; thus, Yangming Couli diseases borrow Chaihu for resolution. Thus, Yangming's failure to hold implies either Taiyang insecurity or Shaoyang unpreparedness. Hence, Two Yangs often combine to cause disease.

If pathogen is already in Yangming territory, must send troops to vigorously drive it out, leaving none behind; hence use Zhizi Chi Tang (Gardenia and Fermented Soybean Decoction) and Gua Di San (Melon Tip Powder) for vomiting to sweep quickly. If deeply penetrating the interior, cannot drive out, then scorched earth policy (clear fields for a thousand li) deprives them of plunder; this is where Baihu Tang excels. If pathogen is in the inner court, must clear internal Yin thieves; this is how Chengqi formulas win. Agents like Yinchen (Artemisiae Scopariae Herba) and Zhuling (Polyporus) legislate for undisciplined armies.

Taiyin is also interior; Shaoyin/Jueyin territories are Taiyin's borderlands. Taiyin occupies the Central Plain, connecting externally to Three Yang, but Yin/Yang paths diverge, with diaphragm barriers between Heart/Abdomen. Thus, Cold-Water pathogens from Taiyang exterior invasion are light; from Shaoyin interior transmission are heavy. Wind-Wood pathogens from Shaoyang invasion are slight; from Jueyin upward assault are severe. If original pathogen transfers to Yangming becoming excess, like exhausted troops, purging cures it. If Yangming excess transfers to original channel becoming deficiency, pathogen strong/deficiency weak, warming/tonifying recovery is difficult.

Though Taiyin and Yangming territories are separate, there is no barrier. Yangming is a thoroughfare for enemies, gathering troops, a four-battle ground. Taiyin is a granary, relied upon by armies, also a bandit nest. If Yuan Qi is sufficient, pathogen enters Yangming; if insufficient, enters Taiyin. In Yangming territory, deploy troops for a decisive battle, winning quickly. In Taiyin territory, granaries burned/looted, empty stores, starving soldiers cannot resist.

Jueyin territory is the zone of Ministerial Fire circulation. Its original Qi is Minor Fire; if wind-cold-dryness-dampness enters, it transforms entirely into Heat, i.e., Major Fire. Minor Fire is the life force of the body; Major Fire is the great disaster. Its territory connects to Sanjiao. Pathogen attacking Upper Jiao causes Qi rushing to Heart, burning pain in Heart, thirst, oral ulcers, sore throat/obstruction. Pressing into Middle Jiao causes cold extremities, faint pulse, hunger without desire to eat, vomiting roundworms after eating. Moving to Lower Jiao causes dysentery with heaviness, or pus/blood in stool, causing deep harm, like a rebellious army.

Zhang Zhongjing formulated Wu Mei Wan (Mume Pill), using cold/heat together, attacking/tonifying simultaneously, regulating Qi/Blood, harmonizing Sanjiao, as the main formula for pacifying Jueyin, like a Grand Commander of the interior. Giving water for thirst, Fuling Gancao Tang (Poria and Licorice Decoction) for water retention, Zhigancao Tang (Processed Licorice Decoction) for restoring pulse, Danggui Sini Tang (Angelica Frigid Extremities Decoction) for cold extremities—these are elite troops sent separately to rescue the Heart Master in Upper Jiao and calm the Spirit. Using Baihu/Chengqi types clears Stomach and calms Middle Jiao heat-excess; Baitouweng Tang (Pulsatillae Decoction) and Sini San (Frigid Extremities Powder) clear Spleen and stop Lower Jiao heat-dysentery, rescuing Yin in the Abdomen and supporting Stomach Qi.

Kidney is one Fu organ but divides into Yin/Yang channels. Shaoyin is one channel but combines Yin/Yang Zang, being the root. Thus, pathogens have Yin/Yang paths; Zang divides Yin/Yang Qi. If Yang pathogen attacks Shaoyin-Yang, reverse fever, vexation, cough/thirst, sore throat. If Yang pathogen attacks Shaoyin-Yin, abdominal pain, spontaneous diarrhea, or pus/blood in stool. If Yin pathogen attacks Shaoyin-Yang, body/joint pain, cold extremities, back aversion-to-cold, lethargy. If Yin pathogen attacks Shaoyin-Yin, aversion-to-cold, vomiting, clear grain diarrhea, restlessness desiring death.

Zhang Zhongjing formulated Mahuang Fuzi Xixin Tang (Ephedra, Prepared Aconite, and Asarum Decoction), Huanglian Ejiao Tang (Coptis and Donkey-Hide Gelatin Decoction), Gancao Jiegeng Tang (Licorice and Platycodon Decoction), Zhufu Tang (Pig Skin Decoction), Banxia Kujiu Tang (Pinellia and Vinegar Decoction) to defend against Yang pathogens attacking Shaoyin-Yang. He formulated Taohua Tang (Peach Blossom Decoction) and Zhuling Tang (Polyporus Decoction) to defend against Yang pathogens entering Shaoyin-Yin. Fuzi Tang, Wuyu Tang (Evodia Decoction), Sini Tang defend against Yin pathogens attacking Shaoyin-Yang. Tongmai Sini Tang (Pulse-Restoring Frigid Extremities Decoction), Fuling Sini Tang, Ganjiang Fuzi Tang defend against Yin pathogens entering Shaoyin-Yin.

Shaoyin is the root of six channels, connecting externally to Taiyang and internally to Yangming. Thus, initial reverse fever and fever of whole body/extremities after 8-9 days indicate Shaoyin-Yang pathogen invading Taiyang territory. Spontaneous diarrhea of pure green water, epigastric pain, dry mouth/tongue indicate Shaoyin-Yang pathogen invading Yangming territory. Exiting Taiyang, use Mahuang as vanguard supervised by Fuziu; entering Yangming, rely fully on Dachengqi without supervision, like using guides differently from main troops. Yin pathogens invading Taiyin use Lizhong Tang (Regulate the Middle Decoction) and Sini plus Human Urine/Pig Bile, similarly.

Alas! Without pondering Zhang Zhongjing's compilation, how can one see the disease and know its origin?