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A-Jiao (Donkey-Hide Gelatin) is the supreme medicine for nourishing blood; regardless of which meridian is affected, it falls within its therapeutic scope. Its flavor is rich and yin in nature; A-Jiao has the richest flavor among medicines, so it must be used for tonification, and should not be used when tonification is inappropriate. When added to Baitouweng Tang (Coptis Decoction), it is indicated for severe deficiency due to dysentery; when added to Neibu Danggui Tang (Internal Nourishment Angelica Decoction), it is indicated for excessive blood loss. Both Zhang Zhongjing and Sun Simiao have given clear instructions on this. However, A-Jiao is not a substance for filling voids and cannot be discussed on par with Shudi Huang (Rehmanniae Radix Preparata) or Shanyao (Dioscoreae Rhizoma). A-Jiao is prepared by decocting black donkey hide from Ji River water; its nature tends to descend and it lubricates the large intestine, making it unsuitable for diarrhea. Why then does Baitouweng Jia Gancao E'jiao Tang (Baitouweng Decoction plus Licorice and Donkey-Hide Gelatin) treat diarrhea? This is because it treats heat-dysentery with stagnation, precisely utilizing its lubricating property. Thus, Zhang Jiegu uses it in Jiajian Pingwei San (Modified Pingwei Powder) for heat-dysentery with abundant pus. Thirst that is not caused by heat consuming fluids implies that yin fluids from the lower jiao fail to ascend. A-Jiao cannot clear heat and its nature descends, so how can it stop thirst? Zhu Ling Tang (Polyporus Decoction) treats fever with thirst and also diarrhea with thirst; although the syndrome is generally unsuitable for A-Jiao, it is paradoxically combined with it. This is because the thirst and diarrhea are caused by heat, with water retention in the middle jiao where heat and water interact, leading to severe fluid injury. If one were to administer diuretic and drying agents like Zhu Ling (Polyporus), would not the fluids be nearly exhausted? Therefore, adding A-Jiao serves to moisten fluids and correct the bias of Zhu Ling and similar herbs, rather than treating the thirst and diarrhea directly. Extending this logic, Huotu Tang (Yellow Earth Decoction) dries dampness, Biejia Jian Wan (Turtle Shell Pill for Breaking Stagnation) breaks accumulations, Wenjing Tang (Warming the Menses Decoction) moves blood stasis, and Dahuang Gansui Tang (Rhubarb and Kansui Decoction) purges blood and drives out water; none of these actions can be achieved by the moistening, greasy, and descending nature of A-Jiao. Generally, because A-Jiao nourishes blood and moistens fluids while descending, it does not hinder the actions of drying dampness, breaking stagnation, moving stasis, purging blood, or driving out water, and it can assist where they fall short, hence its necessity. If one rigidly applies the principles of Huotu Tang and demands that A-Jiao perform tasks like drying dampness, it would be no different from the limited perception of touching a candle in the dark or listening to a pot.

Regarding Xi Jiao (Rhinoceros Horn), some say it is a stomach herb, others say it is a heart herb; some claim its nature ascends, others that it descends; some say it induces sweating most rapidly, others that its use for blood disorders contradicts classic teachings. Poisonous substances dissolve upon entering the earth; cattle belong to earth, and Xi Jiao features yellow flowers within black and black flowers within yellow. Although associated with water retention, it embodies the virtue of earth, justifying its classification as a stomach herb. *Shiming* states: "The heart is delicate; what it perceives penetrates even the subtlest details." Xi Jiao contains white stars penetrating both ends and shines brightly at night, justifying its classification as a heart herb. Its horn is long and sharp, hollow and ventilated, with a bitter, sour, salty, and cold taste. Thus, it can reach the highest and lowest extremes, as well as the innermost and outermost extremes. In reality, it neither ascends nor descends, does not induce sweating, and does not purge excess. It is a heart and stomach herb but does not exclusively target them; it is a blood herb but does not indiscriminately treat all blood disorders. Observing *Qianjin Fang* and *Waitai Miyao*, cases using Xi Jiao include those affecting the upper, middle, lower, exterior, and interior. Regardless of location, it is suitable only for blood-heat with toxicity. Various theories are inevitably biased.

When discussing the essence of Xi Jiao, Zou's theory is paramount. However, he claims that using Xi Jiao requires an exterior syndrome accompanied by skin lesions, yet the cases he cites from *Waitai Miyao* show no exterior syndrome. An exterior syndrome refers to pathogenic factors on the exterior requiring sweating. While Xi Jiao is sometimes used with Mahuang (Ephedrae Herba), it cannot be solely relied upon to induce sweating. Zou argues that the absence of Xi Jiao in Shengma Biejia Tang (Cimicifuga and Turtle Shell Decoction) indicates no exterior syndrome, while its presence in *Waitai Miyao* for sore throat indicates an exterior syndrome. However, Shengma Biejia Tang syndrome involves sore throat, so his reasoning is flawed.

Zou quotes Wei Pei's playful remark that Xi Jiao is "upside-down Dahuang" (Rhei Radix et Rhizoma). This elaborates that Dahuang treats fire rising from the center downwards, while Xi Jiao treats fire rising from the bottom upwards. The meaning is profound but incomplete. According to *Ben Jing*, Dahuang treats stagnant blood in the lower body, while Xi Jiao resolves hundred toxins. From this, we deduce that Dahuang clears heat-stagnation in the blood level by purging downwards. Xi Jiao clears heat-toxicity in the blood level by resolving and dispersing. Dahuang does not mention detoxifying because heat-stagnation occurs in deficient areas, primarily affecting the intestines and stomach. Xi Jiao does not mention purging blood because heat-toxicity invades solid areas, primarily affecting the skin and muscles. Dahuang is extremely bitter, yellow, and fierce in nature, naturally driving pathogens downward. Xi Jiao is a spiritual substance that rushes to any location encountering toxicity. Claiming it descends from above and ascends from below is improper praise.

Lu Jiuzhi's *Xi Jiao Shengma Bian* in *Shibuzhai Yishu* appears detailed but is actually quite flawed. Using Shengma (Cimicifugae Rhizoma) to replace Xi Jiao appears in Sun Simiao's *Qianjin Fang*, predating Zhu Fengyi's *Huo Ren Shu*. Both herbs are hollow and ventilated, enter the Yangming meridian, have bitter flavors that can vent, and thus *Ben Jing* states both resolve hundred toxins. However, Shengma governs Qi, while Xi Jiao governs Blood. Shengma raises Yang Qi and resolves toxicity; Xi Jiao clears blood-heat and resolves toxicity. They are distinct and seemingly not interchangeable. Sun Simiao used various formulas with Xi Jiao, but specifically in *Muxiang Tang* (Costus Decoction) under Cold Damage and Miscellaneous Treatments, stated that for severe heat-toxicity, add Xi Jiao, or substitute with Shengma if unavailable. The treated condition was painful sores where Yang Qi was depressed by Yin pathogens, requiring acrid-warm Yang-promoting herbs like Muxiang (Aucklandiae Radix). Since heat was severe and toxic, Shengma could resolve toxicity and raise Yang without hindrance, allowing substitution. Zhu Fengyi applied this method to Xijiao Dihuang Tang (Rhino Horn and Rehmannia Decoction), inviting Lu's criticism, yet Lu himself erred. The concepts of "lifting pathogens outward" and "leading pathogens inward" have existed for a long time; I dare not refute them based on personal opinion alone. However, Zhang Zhongjing's *Shanghan Lun* and *Jingui Yaolue* strictly distinguish between releasing the exterior and purging the interior. Even when using sweating methods on Yin meridians, unless Taiyang pulse/syndromes are present, the pathogen is on the exterior or upper body. If the pathogen leaves its original meridian to enter another, treatment targets that specific meridian, allowing the pathogen to resolve naturally through medication, not by "lifting" it to migrate before resolution. Zhang Zhongjing repeatedly warned against sweating when the pathogen is not in the interior, which is well documented. Does Lu know that lifting pathogens outward requires them to be on the exterior/upper body first? Pathogens suitable for sweating are originally on the exterior/upper body; there is no record of lifting them from the interior/lower body to induce sweating. Some argue Shengma's name implies ascending action. However, Shengma raises Yang Qi from the deepest Yin. Zhou Shenzhen said: "All disease sites are Yin or Fire, where Yang Qi does not reach. Shengma raises Yang Qi to cure disease, not to lift pathogenic Qi away from the site; they cannot be conflated." Leading pathogens inward should be termed "causing" rather than "leading." Disease-free areas are first damaged by drugs, allowing pathogens to enter via deficiency due to drug error, unlike objects attracting each other. If cold drugs treat cold diseases and hot drugs treat hot diseases, one might call pathogens "led" by drugs. However, this merely exacerbates the primary disease, causing no new complications. Lu cites Yu's case of Mrs. Zhao, mistakenly using Xi Jiao to lead pathogens to attack the Heart, to prove Xi Jiao is not a stomach herb. Indeed, misuse of Xi Jiao causes severe harm. But claiming it is not a stomach herb shows shallow understanding. He also claims Xi Jiao treats "Heat Entering the Blood Chamber" by extracting pathogens from the deepest obscurity, hence calling it "ascending." Besides, Xi Jiao does not extract pathogens. There is no such treatment principle as extracting pathogens from deep obscurity by ascending. Zhang Zhongjing treats Heat Entering the Blood Chamber with Xiao Chaihu Tang (Minor Bupleurum Decoction), which seems ascending. However, in *Shanghan Lun* and *Jingui Yaolue*, only the case with intermittent chills and fever after initial onset prescribes Xiao Chaihu Tang, emphasizing this symptom to indicate it is not a general formula for this condition. The Liver and Gallbladder meridians function mutually. Although heat enters the Liver, chills and fever resembling malaria indicate the pathogen remains in Shaoyang. Xiao Chaihu Tang harmonizes, which fits best. Chaihu (Bupleuri Radix) belongs to harmonization; how can Xi Jiao be called ascending? *Huo Ren Shu* erroneously adds "Xiao Chaihu Tang is appropriate" to the *Shanghan Lun* line about water flow stopping during menstruation, daytime clarity, and evening delirium as Heat Entering the Blood Chamber, treating Xiao Chaihu Tang as a universal remedy, which is extremely crude.

Someone questioned me: You state that lifting pathogens outward applies only when pathogens are on the exterior/upper body. Yet *Yuyi Cao* records Zhou Xinchuan's rest dysentery cured by Yu's "Counter-current Boat Pulling" method, lifting internalized pathogens outward. Why are you so rigid? I replied: The "Counter-current Boat Pulling" theory is often criticized by later generations. Actually, it does not literally lift pathogens to the exterior, and it secretly aligns with Zhang Zhongjing's principles, which can be verified by cross-referencing. Yu's *Dysentery Discussion* states: "Dysentery must first resolve the exterior through sweating, then regulate the interior; this is the key for early-stage dysentery, which students must remember." For chronic dysentery resulting from missed exterior release, where pathogens have deeply invaded, claiming "Counter-current Boat Pulling" extracts them externally ignores where the pulling originates. Pulling upward from the extreme lower body violates the prohibition against sweating for Shaoyin interior syndromes. Yu's analogy is excessive and potentially harmful. *Jingui Yaolue* states: "Diarrhea with wiry pulse, fever, and spontaneous sweating will heal spontaneously." Yu interprets this as chronic dysentery requiring counter-current pulling to explain the healing. Wiry pulse belongs to Shaoyang. In cold-type diarrhea, it signifies declining pathogenic Qi and recovering Yang Qi. Yu forces his interpretation, fabricating arguments, which should not serve as a model. So why did this method cure Zhou Xinchuan's rest dysentery? The patient was 73 years old, with puffy face and eyes, dark skin, and no other symptoms, indicating Yang deficiency and Yin excess. Dysentery has cold and hot types; this was likely cold dysentery with heavy dampness and light heat. Due to sinking Yang Qi struggling with damp-heat, the pulse was deep, rapid, and forceful. Yu's claim of Yang pathogens sinking into Yin is incorrect. The disease is in the intestines/stomach, unrelated to Shaoyin. Comparing it to Zhang Zhongjing's use of Xiao Chaihu Tang for Yangming disease to induce sweating: In Yangming, upper jiao blockage prevents fluid descent, causing stomach disharmony and constipation. Here, pathogenic obstruction in intestines/stomach prevents fluid distribution and transmission, causing chronic dysentery. Xiao Chaihu Tang harmonizes the exterior, leading to slight sweating due to upper jiao unblocking. Rest dysentery normally cannot be sweated; taking Renshen Baidu San (Ginseng and Toxin-Expelling Powder) produces apparent sweating because raising Yang transforms dampness, harmonizing Yin and Yang, allowing grain essence to nourish the skin and body. Although Renshen Baidu San contains Renshen (Ginseng Radix), it is ultimately a draining formula, so Bu Zhong Yi Qi Tang (Middle-Warding and Augmenting Qi Decoction) was used to complete the cure. The Chaihu, Renshen, Gancao (Licorice Root), Shengjiang (Fresh Ginger), and Dazao (Jujubae Fructus) in the latter constitute Xiao Chaihu Tang minus Huangqin (Scutellariae Radix) and Banxia (Pinelliae Rhizoma). The former involved heat; this involved cold. The former required unblocking; this required consolidating. Hence, Huangqin and Banxia were unnecessary. Furthermore, Zhang Zhongjing's formulas for cold diarrhea never include purgatives, sometimes using Shizhi Yuliang (Kaolin and Calcined Oyster Shell) to consolidate the lower or Congbai (Allii Fistulosi Bulbus) to raise Yin (see Congbai for details). Yu externally bandaged the anus to prevent Qi leakage and internally administered decoctions to raise it. He grasped Zhang Zhongjing's intent without rigidly copying his formulas; only a wise person could achieve this. Although Zhang Zhongjing also used counter-current boat pulling to treat diarrhea, Yu's application as "lifting pathogens to the exterior" may lack careful observation.