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Note: Chai Hu (Bupleuri Radix) is classified as a herb for the Shaoyang (Lesser Yang) channel because it is the key ingredient in formulas used for Shaoyang syndrome in cold damage diseases. When pathogenic factors enter the Shaoyang, there is often a trend where exterior pathogens gradually resolve while interior pathogens intensify. Therefore, in such formulas, Chai Hu and Huang Qin (Scutellariae Radix) are juxtaposed to achieve the harmonizing method of Shaoyang by releasing the exterior and clearing the interior. However, Chai Hu has not been strictly fixed as a herb exclusive to the Shaoyang channel. This is because Chai Hu possesses a bitter, neutral, slightly cold nature, with a light flavor and ascending aroma, which aptly suits the treatment of pathogens located at the half-exterior half-interior level.

As for the assertions that "administering Chai Hu too early when the disease is in the Taiyang (Greater Yang) stage will invite the thief into the house" and "if Chai Hu is taken after the disease has entered the Yin channels, it will further deficiency the exterior," these warnings likely stem from concerns that later practitioners might vaguely misuse half-exterior half-interior herbs due to unclear diagnosis. Thus, these two scenarios were established to clarify this point. Have we not observed various formulas in Zhang Jingyue's *New Formulas*, such as various Chai Hu Decoctions, Chai Qin Decoction, and Chai Hu Baihu Decoction? He applied them effortlessly and appropriately, demonstrating a clear understanding of Chai Hu's utility, which aligns perfectly with my own views. Furthermore, ancient formulas include Xiaoyao San (Free and Easy Wanderer Powder) for dispersing constrained heat, Guichai Yin (Angelica and Bupleurum Decoction) for harmonizing Ying (Nutritive) level and dispersing pathogens, Buzhong Yiqi Tang (Tonify the Middle and Augment the Qi Decoction) for raising clear Yang and lifting sinking pathogens, and Shugan Yishen Tang (Soothe Liver and Benefit Kidney Decoction) for soothing the liver, clearing heat, nourishing Yin, and venting pathogens. Their subtleties are numerous and difficult to enumerate; how could they cause further deficiency of the exterior? When I use Chai Hu for mild cases of initial wind-pathogen invasion or for chronic conditions where pathogens linger and exterior heat persists, it yields miraculous effects. Why should one fear this useful, high-quality herb due to rigid adherence to old theories? Even if used, its dosage is strictly limited, leading to a customary practice that I feel compelled to refute.

Regarding Zhu Nanyang's statement that "if Rhinoceros Horn is unavailable, Sheng Ma can be used as a substitute" on the grounds that both have venting properties, Zhu Eryun argued against this, citing the significant difference in their ascending and descending actions. I consider this not to be a definitive conclusion. Rhinoceros Horn (Rhinocerotis Cornu) is a substance for clearing heat and venting pathogens, whereas Sheng Ma (Cimicifugae Rhizoma) is a substance for ascending and venting. One emphasizes clearing heat, while the other emphasizes ascending action; their natures differ, and thus their applications naturally diverge. It has never been heard that substances with different natures can be substituted for one another. If wind-cold is congested and obstructed, preventing the eruption of rashes, this falls under the responsibility of Sheng Ma. Conversely, if warm pathogens cause erythema and macules to appear intermittently, this is governed by Rhinoceros Horn. If Sheng Ma were used as a substitute, patients with lung-heat would inevitably suffer from sore throat, potentially worsening wheezing and counterflow qi. Patients with heat in the Ying (Nutritive) level would inevitably experience hematemesis, or at least epistaxis. Such errors are severe; how can substitution be justified? Moreover, since Rhinoceros Horn grows on the head, it is used as a venting agent. Zhu Eryun's claim that it is a descending substance also requires refutation. I dare not lightly criticize predecessors, but out of sincere concern, I have cautiously discussed this matter.