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Blood Residue Char (Xueyu Tan, charred human hair) is hair. If not processed, its texture cannot be transformed; therefore, it must be converted into charcoal before being used in medicine. Its properties can resolve blood stasis and generate new blood, resembling Sanqi (Notoginseng Radix). Thus, it is effective in treating hematemesis (vomiting blood) and epistaxis (nosebleed). Long-term consumption can also treat Laozhai (consumptive disease/tuberculosis), as patients with this condition inevitably have both blood deficiency and stasis; hence, the *Jingui Yaolue* refers to it as Xuebi Xu Lao (blood bi and deficiency exhaustion). Human hair originates from the heart's blood; consuming it allows for self-restoration through "using human to tonify human," a subtle妙 effect that prevents blood deficiency. Furthermore, its power to resolve stasis makes it excellent for treating Xuebi (blood obstruction); thus, long-term use naturally yields results. Its nature also promotes urination (the *Jingui Yaolue* contains formulas for promoting urination such as Gaofa Jian [Hair Paste Decoction]). Since half of human urine exudes from blood vessels, Blood Residue Char resolves stasis and generates new blood, facilitating vascular circulation, thereby producing this effect. Its ability to resolve stasis and generate new blood also effectively treats bloody stools with a foul odor, intestinal rot, and amenorrhea (closure of menstruation) in women where menses do not arrive on time.

Method for preparing Blood Residue Char: Take hair shaved from young adults, wash it clean with alkaline water, then rinse with clear water to remove the alkaline taste. Dry it, then stir-fry in an iron wok until the hair transforms completely into a paste-like state. Cool it, grind it finely, and sieve it. Any hair particles not fully transformed may be fried again.

Nail (Zhijia): Also known as Jintui, it is the surplus of tendons. Crush it, roast until scorched, and grind into powder for use. Its taste is slightly salty, possessing opening and breaking properties. Applied externally to sores and ulcers that are about to rupture but have not yet done so, it accelerates rupture. Internally, it induces labor and expels the placenta. Inhaling its scent stops nosebleeds, and applying it to the eyes eliminates eye nebulae (corneal opacities). I have independently prepared a Nebula-Grinding Eye Drop solution; for dense opacities, adding Nail Powder to other herbs and grinding them together for eye application has proven effective repeatedly.

The treatment of Shanghan (Cold Damage) is categorized by Six Channels chapters. However, there are six channels in the hands and six in the feet, totaling twelve channels. Why does the *Shanghan Lun* divide them into only six channels when there are twelve? According to the *Neijing*’s discussion on the twelve channels, whenever a channel is mentioned without specifying whether it is a hand or foot channel, it refers to the foot channel. When referring to hand channels, it explicitly states "Hand [Name] Channel." This is likely because foot channels are longer and larger than hand channels, which are shorter and smaller; thus, foot channels can encompass hand channels. Mentioning only the foot channel implicitly includes the hand channel. The *Shanghan Lun*’s division into six channels follows the *Neijing*’s convention, embedding hand channels within foot channels. Those who interpret the *Shanghan Lun* claiming that all six channels mentioned are solely foot channels fail to understand Zhang Zhongjing’s profound intent in writing the treatise.

A "Channel" (Jing) is where Qi and Blood flow. When a Zang-Fu organ connects with a specific channel, it becomes the "House" (Fu) of that channel. The flowing Qi and Blood originate from the House, and external pathogens invading internally often settle in the House. Below, the twelve hand and foot channels and their respective Houses are listed in detail.

Although there are twelve hand and foot channels, they are named according to six categories because the names for hand and foot channels are originally identical. The channels are Yin or Yang. Yang channels are divided into Taiyang, Yangming, and Shaoyang; Yin channels are divided into Taiyin, Shaoyin, and Jueyin. Yin and Yang channels are exterior-interior pairs: Taiyang and Shaoyin are paired, Yangming and Taiyin are paired, and Shaoyang and Jueyin are paired. Pairs exist because their Yin and Yang meridians run parallel, with Yang operating on the exterior and Yin on the interior. Regarding the association of channels with Houses: the House of the Foot Taiyang Channel is the Bladder; the House of the Foot Shaoyin Channel is the Kidney; the House of the Foot Yangming Channel is the Stomach; the House of the Foot Taiyin Channel is the Spleen; the House of the Foot Shaoyang Channel is the Gallbladder; and the House of the Foot Jueyin Channel is the Liver. These constitute the three Yin and three Yang channels of the feet and their Houses.

The House of the Hand Taiyang Channel is the Small Intestine; the House of the Hand Shaoyin Channel is the Heart; the House of the Hand Yangming Channel is the Large Intestine; the House of the Hand Taiyin Channel is the Lung; the House of the Hand Shaoyang Channel is the Sanjiao (Triple Burner); and the House of the Hand Jueyin Channel is the Pericardium. These constitute the three Yin and three Yang channels of the hands and their Houses.

Yang channels are the exterior of Yin channels, and the Taiyang Channel is the exterior of the exterior. Its main pathway is along the back, actually forming the outer boundary of the entire body. The Ying (Nutritive) Blood and Wei (Defensive) Qi of the body rely on it for protection and integration. It possesses sufficient thermal energy to defend Ying and Wei against internal invasion by external pathogens. Therefore, the *Neijing* calls it Ju Yang (Giant Yang). Tracing the source of this heat, it stems from the Ministerial Fire (Xiang Huo) and Sovereign Fire (Jun Huo). Sovereign Fire originates in the heart’s blood vessels and circulates with the lungs, dissipating heat into the Great Qi in the chest (also called Zong Qi), which extends outward to nourish Ying and Wei. This is like the sun high in the sky radiating heat downward; hence, its name is Taiyang. Ministerial Fire originates in the Mingmen (Gate of Life) within the kidneys. Although the kidney belongs to Water, it harbors Ministerial Fire. The steaming vapor of water and fire penetrates from the bladder through the fatty membranes connecting to the Sanjiao to reach the body's surface. This is akin to the earth’s core water-fire energy penetrating the ground in spring to generate heat. Since this heat arises from within water, the Taiyang Channel is also called the Taiyang Cold Water Channel. Because the heat of the Taiyang Channel derives from both Sovereign and Ministerial Fires, its House is not only the Bladder but also the Chest. This is evident from the fact that formulas such as Xianxiong Decoctions/Pills and Xiexin Decoctions in the *Shanghan Lun* are listed under the Taiyang chapter.

Regarding the sequence of transmission among the six channels in Shanghan disease, the *Suwen* chapter of the *Neijing* details it: "When humans are injured by cold, they develop fever. On the first day, Ju Yang receives it, causing headache, neck stiffness, and back rigidity. On the second day, Yangming receives it; Yangming governs muscles, and its vessels clamp the nose and connect to the eyes, causing body heat, eye pain, dry nose, and inability to lie down. On the third day, Shaoyang receives it; Shaoyang governs the gallbladder, and its vessels follow the flanks and connect to the ears, causing hypochondriac pain and deafness. When the meridians of the three Yang channels are affected but the pathogen has not entered the Zang organs, sweating can cure it. On the fourth day, Taiyin receives it; Taiyin vessels distribute in the stomach and connect to the throat, causing abdominal fullness and dry throat. On the fifth day, Shaoyin receives it; Shaoyin vessels pass through the kidneys, connect to the lungs, and tie to the root of the tongue, causing dry mouth, dry tongue, and thirst. On the sixth day, Jueyin receives it; Jueyin vessels follow the genitalia and connect to the liver, causing irritability, fullness, and retraction of the scrotum." When pathogens enter the Fu organs via the meridians, purgation can cure them. This is the *Neijing*’s account of the six-channel transmission sequence. The *Shanghan Lun* follows the *Neijing*’s order for the six channels but does not explicitly state that transmission occurs one channel per day. In my clinical experience, I have seen cases where Shanghan persisted in the Taiyang House for ten days. The timing of transmission to other channels is not fixed. The *Neijing* describes the norm, but pathological changes often exceed standard examples. Transmission to a specific channel presenting corresponding symptoms is not absolute. Investigating the causes and combining them with my clinical experiments, I know that presenting symptoms of a specific channel upon transmission often indicates prior internal injury in that channel. Without internal injury, transmission to a channel may not immediately present its characteristic symptoms. This requires careful observation by the clinician.

As for the naming of the six channels, hand and foot names are identical, but some are named after the originating House of the hand channel, while others are named after the originating House of the foot channel. For example, the Taiyang Channel is named the Taiyang Cold Water Channel, derived from the Foot Taiyang House, and the Hand Taiyang is also named Taiyang Cold Water Channel, linking the hand channel to the foot channel. Similarly, the Yangming Channel is named the Yangming Dry Metal Channel, derived from the Hand Yangming House (Large Intestine belongs to Metal, and its paired Lung also belongs to Metal); the Foot Yangming is also named Yangming Dry Metal Channel, linking the foot channel to the hand channel. The Shaoyang Channel is named the Shaoyang Ministerial Fire Channel, derived from the Foot Shaoyang House (Gallbladder houses Ministerial Fire); the Hand Shaoyang is also named Shaoyang Ministerial Fire Channel, linking the hand channel to the foot channel. The Taiyin Channel is named the Taiyin Damp Earth Channel, derived from the Foot Taiyin House (Spleen is Damp Earth); the Hand Taiyin is also named Taiyin Damp Earth Channel, linking the hand channel to the foot channel. The Shaoyin Channel is named the Shaoyin Sovereign Fire Channel, derived from the Hand Shaoyin House (Heart is Sovereign Fire); the Foot Shaoyin is also named Shaoyin Sovereign Fire Channel, linking the foot channel to the hand channel. The Jueyin Channel is named the Jueyin Wind Wood Channel, derived from the Foot Jueyin House (Liver belongs to Wood and governs Wind); the Hand Jueyin is also named Jueyin Wind Wood Channel, linking the hand channel to the foot channel. This explains the rationale for merging the twelve hand and foot channels into six.