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At the onset, chills and fever appear, resembling Taiyang disease (diseases caused by pathogenic factors affecting the Taiyang channel), but accompanied by pain or swelling in the feet and knees. Although initially caused by sitting or lying on damp ground, wading through water, or walking on ice, over time it inevitably transforms into heat, thus belonging to Damp-Heat. The *Classic* states: "All swellings and fullness due to dampness belong to Spleen Earth." It also says: "When injured by dampness, the lower part of the body is affected first." This is because the Spleen governs the four limbs, and the feet are located below, easily receiving dampness. When dampness stagnates and generates heat, Damp-Heat combats each other, causing pain. Therefore, it was anciently named "Yong Ji" (Obstruction Disease), and should be treated with agents that promote circulation and unblockage, such as Qianghuo Daoshi Tang (Notopterygium Decoction for Removing Stagnation) or Danggui Niantong Tang (Angelica Sinensis Decoction for Relieving Pain). By ensuring Qi does not stagnate, the pain will heal itself. There was no concept of "Hongxiang Jiao" (Foot Qi/Jock Itch equivalent in TCM context, often referring to Beriberi-like symptoms) in ancient times; the *Neijing* called it "Jue" (Reversal/Cold Extremities); during the Two Han Dynasties, it was called "Huan Feng" (Sluggish Wind); after the Song and Qi dynasties, it was termed "Hongxiang Jiao". Cases with swelling are named "Shi Hongxiang Jiao" (Damp Foot Qi), characterized by flaccid and soft tendons and vessels, edema, or sores; treatment should focus on draining dampness and dispersing wind. Cases without swelling are named "Gan Hongxiang Jiao" (Dry Foot Qi), where "dry" implies heat, characterized by contracted, cramping, painful tendons and vessels, dryness, thinness, and lack of swelling; treatment should focus on moistening blood and clearing dryness. Some arise from external pathogens, others from internal injury, but both are essentially Damp-Heat. In the North, the terrain is high and dry; people drink milk and cheese, eat meat, and drink alcohol, leading to Damp-Heat flowing downward. In the South, the terrain is low and humid; people with weak Qi and Blood, due to sexual indiscretion, carrying heavy loads over long distances, or exposure to rain and snow, suffer from Cold-Damp invading due to deficiency. Generally, Wind, Cold, Summerheat, and Dampness invading the Yang channels cause exterior diseases, with symptoms mostly at the lateral malleolus and dorsum of the foot, treatable by dispersing. Invading the Yin channels causes interior diseases, with symptoms mostly at the medial malleolus and sole, treatable by warming and promoting urination. Exterior signs: spontaneous sweating and migrating pain indicate Wind excess; no sweating, painful stiffness indicates Cold excess; swelling and heaviness indicate Damp excess; irritability, thirst, and numbness indicate Summerheat excess. If all four pathogens are present, identify the predominant one. "Jue" is due to Wind; "Pain" is due to Cold; "Swelling" is due to Damp. Cold excess feels like insects crawling on the skin; Heat excess leads to flaccidity. All six foot meridians can be affected, but none of the hand meridians are involved. Cold is treated with warmth; Heat with cooling. Exterior conditions are dispersed; Interior conditions are purged. If there is severe deficiency, tonifying decoctions are used intermittently, chosen according to the cold or heat nature of the disease. One must not be rigid. Dark and thin individuals are easier to treat; fat, pale, or reddish individuals are difficult to cure. Dark-skinned people tolerate Wind-Damp; pale/reddish people do not. Thin people have firm flesh; fat people have soft flesh. Medication must distinguish between Deficiency/Excess, Cold/Heat, and Exterior/Interior. Huangqin (Scutellariae Radix) and Cangzhu (Atractylodis Rhizoma) are essential for Damp-Heat. Fangji (Stephaniae Tetrandrae Radix) and Duhuo (Angelicae Pubescentis Radix) treat Damp-Heat swelling from the waist down to the feet. Mugua (Chaenomelis Fructus) enters the Liver and benefits tendons. Chifuling (Poria Cocos with Red Sandalwood) and Mutong (Akebiae Caulis) drain dampness. Rougui (Cinnamomi Cortex) and Wufulzi (Aconiti Lateralis Radix Praeparata) disperse Cold-Damp. Muxiang (Aucklandiae Radix), Binglang (Arecae Semen), Xiangfu (Cyperi Rhizoma), and Wuyao (Linderae Radix) are Qi-moving agents. Honghua (Carthami Flos) and Taoren (Persicae Semen) invigorate blood and resolve stasis. Niuxi (Achyranthis Bidentatae Radix), Duzhong (Eucommiae Cortex), Bibai (Dioscoreae Hypoglaucae Rhizoma), and Hugu (Ossis Cornu Tigris - *Note: Tiger bone is banned, historically used*) strengthen bones and tendons. Renshen (Ginseng Radix), Huangqi (Astragali Radix), Baizhu (Atractylodis Macrocephalae Rhizoma), Danggui (Angelicae Sinensis Radix), Shaoyao (Paeoniae Radix Alba/Rubra), and Dihuang (Rehmanniae Radix) tonify Qi and Blood. Used appropriately, both attacking and tonifying methods can succeed. Foot Qi starts subtly and is often unrecognized. Diet and activity remain normal, except for sudden weakness and inability to move the bent foot. Northern and Southern etiologies differ internally/externally, but both stem from Kidney Deficiency. Women suffer this due to Empty Blood Sea, similar to male Kidney Deficiency. If the pathogen ascends to the heart causing persistent vomiting, death is imminent; use Bawei Wan (Eight-Ingredient Pill) to warm and expel. If it enters the Kidneys, causing lumbar/calf swelling, urinary obstruction, black aura around eyes/forehead, chest oppression, wheezing, and groaning, with an absent Left Chi pulse, prognosis is fatal, as Kidney Water overwhelms Heart Fire in those with Kidney Yang Deficiency. Thus, for Kidney Deficiency Foot Qi, Jin Gui Shenqi Wan (Kidney Qi Pill from the Golden Cabinet) should be taken prophylactically.

Southern cases entering from outside manifest only as lower leg swelling/pain; Northern cases arising from inside may reach the hand joints. Initial treatment uses dispersing formulas, followed by purging the bowels to guide out pathogens. The *Classic* states: "Wind blowing after exiting a shelter condenses on skin as Bi (Obstruction), on vessels as Qi (Stagnation), on feet as Jue (Cold Extremities)." The *Treatise on the Great Truth and Essential Principles* says: "Excess of Taiyin Dampness causes internal Fire stagnation, spreading externally, leading to calf swelling, fluid retention internally, and edema below." Internal injury from wine/food damages Spleen/Stomach transport, preventing ascending Qi, which flows down to attack Liver/Kidney, pouring into calves. Combined with sexual excess, pathogens invade deficiency, causing Foot Qi. Chronic cases become stubborn diseases, hard as stone, called "Shi Ju" (Stone Abscess). Red-purple discoloration with ulceration is called "Huan Ju" (Sluggish Abscess). Only warming and tonifying are suitable. Symptoms include vomiting upon eating, aversion to food odor, abdominal pain/diarrhea, constipation/urinary retention, mental confusion, delirium, high fever/headache resembling Taiyang disease. This is "Foot Qi attacking the Heart," often fatal. Dark/thin are easy to treat; fat/white/fleshy are difficult.

Li Dongyuan stated: "For Foot Qi, taking tonics and using herbal washes are absolute taboos." This refers to Southern external Dampness causing swelling/pain, not Northern internal Dampness sinking. For internal Dampness unable to exit, use draining and guiding methods to vent pathogens. If Foot Qi dampness sinks, causing chronic sores/swelling, it becomes a Fistula; use lifting herbs to raise dampness, then adjust Qi/Blood. For Foot Qi attacking the heart, use Siwu Tang (Four Substances Decoction) plus fried Huangbai (Phellodendri Cortex) and Bibai. Apply Wufenzi (Aconiti Lateralis Radix Praeparata) powder mixed with saliva to Yongquan (KI1) acupoint, moxibustion applied to draw heat downward. Three prohibitions: 1. Anger causes Heart Fire, triggering attacks; 2. Loud speech damages Lung, triggering attacks; 3. Exposing feet to wind/water/cold. Abstinence and diet control are key. Pulse floating/wiry indicates Wind; soggy/weak indicates Damp; surging/rapid indicates Heat; slow indicates Cold; thready indicates Deficiency; deep/firm indicates Excess. Knotted pulse stems from Qi stagnation; scattered from worry; tight from anger; fine from sorrow.

For Kidney Wind-Toxin accumulation causing heavy waist/knees, use Weilingxian (Syneilesis Radix) powder, honey pills size of sesame seeds. Take 80 pills with wine initially; mild evacuation of foul matter (green pus, peach gum) indicates toxin removal. If ineffective, take 100 pills at night; follow with porridge. Continue warming tonics. Wind-toxin affects all organs; Heart/Lung meridians start at fingers; Liver/Spleen/Kidney meridians start at toes.

Heel pain may be due to Phlegm or Blood Heat. Blood Heat: Siwu Tang plus Huangbai, Zhimu, Niuxi. Phlegm: Erchen Tang plus Nanxing, Huangbai, Fangji. If toes curl and lack color, it is Kidney Qi Deficiency failing to nourish; use tonification. Heel is source of Du Mai, path of Kidney Meridian, foundation of bones. Heat/swelling/pain here is due to Foot Three Yin Deficient Heat. Danxi said fire arises from extreme Yin Deficiency at Yongquan. Youth with excessive wine/sex often suffer this.

Persistent knee swelling risks "Crane Knee Wind" (Knee swelling with thin calves, wiry/tight pulse). Caused by Three Yin Deficiency and Cold-Damp flow. If Huantiao (GB30) pain radiates to heel with normal skin, deep-rapid/slippery pulse suggests "Fugu Ju" (Bone-Clinging Abscess), toxin adhering to bone due to insufficient Kidney Yang/Qi, causing Yin-Blood stasis and Heat-Pus formation. Long-term Bawei Wan prevents this by warming bones and moving blood. Misdiagnosis as Damp-Heat leads to fatal Qi/Blood depletion when pus forms. Both Crane Knee Wind and Fugu Ju affect those with Kidney Deficiency. Weak True Qi allows deep pathogen invasion. Ancients used Fuzi to warm Kidney Qi and drive herbs to dispel Cold. In deficient bodies, Cold lingers, Extreme Yin generates Yang, Cold transforms to Heat, leading to ulceration. Using Cold/Cool herbs causes disability, contracture, paralysis, Stone Abscess, or Sluggish Abscess. Lower body is distant; only Guizhi and Fuzi can reach it. Kidney governs bones; buttocks/lower body belong to Kidney; only Guizhi/Fuzi enter these meridians to circulate.