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Cassiae Ramulus (Guizhi), with a sweet and pungent taste, possesses a strongly hot nature. It is ascending and belongs to the Yang within Yang. It has slight toxicity. It is the tender tip of Cinnamomi Cortex (Rougui, 肉桂). Its branches resemble those of willow trees, hence it is also called Willow Cinnamon (Liugui, 柳桂). It can treat diseases of the head and eyes in the Upper Jiao (Upper Burner), simultaneously circulating through the arms, harmonizing Ying Blood (Nutritive Blood) and the Muscle Layer (Muscular Level), stopping thirst and inducing sweating, and dispersing pathogenic factors and wind. It enters the Bladder Fu Organ (Bladder Bowel), making it a crucial herb for treating Cold Damage (Shanghan, 伤寒). However, there are indications for its appropriate and inappropriate use; if this distinction is not clearly understood, it may lead to death.

Cassiae Ramulus is an herb of the Foot-Taiyang Meridian (Foot Taiyang Channel). When pathogens enter the Taiyang meridian, headache and fever occur. In cases of headache and fever, Cassiae Ramulus should be used promptly to induce sweating; once sweat is produced, the Muscle Layer is harmonized. The human body is divided into Ying (Nutritive) and Wei (Defensive) aspects. When wind pathogens invade the body, they first affect the Wei aspect, then move from Wei to Ying, from Ying-Wei to the Fu organs, and from Fu to the Zang organs. This progression follows a specific order and must not be disordered.

In Taiyang disease, characterized by headache and fever, the pathogen has entered the Wei aspect but has not yet entered the Ying aspect. Although Cassiae Ramulus is an herb of the Taiyang meridian, it can only dispel pathogens that have entered the Wei aspect, not those that have entered the Ying aspect. In cases where there is fever without headache, it is not a Taiyang syndrome, and Cassiae Ramulus should not be used indiscriminately. Even if initially there is fever and headache, but later the headache ceases while fever persists, the condition has left the Taiyang stage, and Cassiae Ramulus should not be used indiscriminately.

Moreover, Cassiae Ramulus is an herb that induces sweating. When sweat is present, sweating should be stopped; when sweat is absent, sweating should be induced. This is an inevitable principle. However, one must distinguish between situations where sweating can be induced despite existing sweat, and situations where sweating should not be induced despite the absence of sweat. If a patient with Cold Damage has sweated excessively due to other herbs, and the Taiyang headache remains unresolved, Cassiae Ramulus must still be used to harmonize the exterior. This is not because we fear that Cassiae Ramulus will close the pores. Conversely, in Cold Damage with no sweat, sweating is indicated. If sweating fails to produce sweat after administration, it indicates that external pathogens have completely resolved, including those in the Taiyang meridian. Therefore, Cassiae Ramulus should not be lightly used to further open the interstices (Couli, 腠理). This is not out of fear that Cassiae Ramulus will cause excessive sweating. Understanding the reasons for inducing or not inducing sweating, and distinguishing between conditions suitable or unsuitable for sweating, ensures that using Cassiae Ramulus to dispel pathogens will result in no errors, preventing accidental deaths.

Some argue: "Cassiae Ramulus induces sweating and can also cause Yang Collapse (Wangyang, 亡阳). Why did Master Zhang Zhongjing (Zhang Zhongjing, 张仲景) completely overlook this?" For any exterior syndrome that has not dispersed, Guizhi Tang (Cinnamon Twig Decoction) must be used. I am very cautious about this and dare not use it in large doses. Alas! Cassiae Ramulus is an exterior-resolving herb, not a herb causing Yang Collapse. Cases of Yang Collapse following the use of Guizhi Tang occur because the herb was used improperly to resolve the exterior when it was contraindicated, leading to numerous complications. What fault does Cassiae Ramulus bear?

Some ask: "Guizhi Tang is the sacred medicine for cold damaging the Wei aspect. If a patient presents with fever, headache, and neck stiffness, and Guizhi Tang fails to relieve symptoms, instead worsening them, how is this explained?" This is likely due to the excessive use of Cassiae Ramulus. The Taiyang meridian is a Yang meridian. Cassiae Ramulus is a hot herb. When cold qi first enters the Taiyang meridian, the cold is not severe. Using a small dose of Cassiae Ramulus to dispel pathogens allows the fire of the Taiyang meridian to remain calm, making the cold pathogen fearful of heat and easy to resolve. However, using too much Cassiae Ramulus makes the flavor overly hot, stirring up the fire of the Taiyang meridian. Heat generates more heat, assisting the flaming fire of the Stomach, allowing cold pathogens to enter the Stomach. The cold transforms into heat, failing to resolve, while the original Taiyang symptoms persist. Therefore, when using Cassiae Ramulus, one must absolutely avoid excessive use which causes changes; it is best used in small doses to dispel pathogens.

Some doubt: "Guizhi Tang treats Cold Damage by using heat to scatter cold. Scattering cold outward is not expelling sweat outward. Why is there concern about Yang Collapse?" I suspect this arises from misusing Guizhi Tang in non-Cold Damage cases. To use Guizhi Tang correctly, the patient must have contracted Cold Damage in winter and present with headache and neck stiffness. These are signs of cold damaging the Wei aspect. If fever occurs outside of winter, or if there is fever without headache and neck stiffness, these are not signs of Cold Damage invading the Wei aspect. How could this not result in the disaster of Yang Collapse? This is not the fault of Cassiae Ramulus.

Some doubt: "If Guizhi Tang is not used when indicated, allowing pathogens to transmit to other meridians, leaving headache and neck stiffness unchanged, can Guizhi Tang still be used?" When cold damages the Wei aspect and Guizhi Tang is not used promptly to scatter the exterior, allowing pathogens to enter the interior, emergency treatment should target the interior. However, if headache and neck stiffness persist, the pathogen remains in the Wei aspect. Although symptoms seem variable, it is fortunate that the pathogen remains in the Taiyang meridian, in the Wei aspect, and has not fully entered the interior. One can still use Guizhi Tang, reducing its dosage and adding herbs targeting the specific meridian invaded by the pathogen, achieving immediate results. One should not be rigidly confined to attacking only the interior meridian simply because many days have passed.

Some doubt: "Cassiae Ramulus is hot, while Ephedrae Herba (Mahuang, 麻黄) is cold. Their natures are like ice and charcoal. How can they jointly resolve Taiyang pathogens? Moreover, Master Zhang Zhongjing uses them together in a miraculous manner." The answer is: Only by understanding the inversion of Yin and Yang, and the similarities and differences of cold and heat, can one prescribe medicines and be called a divine physician. The difference between Ying and Wei in the human body is significant. When pathogens enter the Wei aspect, cold manifests; when they enter the Ying aspect, heat manifests. One cannot mistakenly view Ying and Wei as belonging solely to the Taiyang meridian without distinction. Cassiae Ramulus dispels cold in the Wei aspect, while Mahuang dispels heat in the Ying aspect. Using Cassiae Ramulus and Mahuang together dispels half of the cold and heat in the Ying and Wei aspects. What is there to doubt? Only when pathogens are on the verge of entering the Ying aspect but have not left the Wei aspect, presenting with either more cold and less heat, or less cold and more heat, might imprecise differentiation and improper treatment fail to quickly resolve pathogens and instead generate other complications. However, in the hands of Master Zhang Zhongjing, combining Cassiae Ramulus and Mahuang is indeed both miraculous and divine.

Some doubt: "Cassiae Ramulus scatters cold pathogens, specifically those in the Wei aspect. Once Cassiae Ramulus is used, shouldn't all cold pathogens in the Wei aspect be scattered? Why would pathogens then enter the Ying aspect? It seems Cassiae Ramulus cannot fully scatter pathogens in the Wei aspect. Could there be other herbs to supplement the insufficiency of Cassiae Ramulus?" The answer is: Regarding Cassiae Ramulus scattering cold in the Wei aspect, I worry it may be excessive, while you worry it may be insufficient. If pathogens enter the Ying aspect after using Guizhi Tang, it is not because Cassiae Ramulus is insufficient to scatter Wei pathogens, but because Cassiae Ramulus was used too late, allowing pathogens to enter the Ying aspect first. What can Cassiae Ramulus do then? This is why early treatment is prized in Cold Damage.

Some doubt: "Guizhi Tang is the vanguard for dispelling pathogens in Cold Damage. Used appropriately, pathogens retreat easily; used inappropriately, they are hard to resolve. How can we ensure the initial use of Guizhi Tang is never inappropriate?" Treating Cold Damage without proper syndrome differentiation leads inevitably to erroneous medication. Hence, ancients spoke of observing symptoms without examining pulses, yet pulse diagnosis is also indispensable. Master Zhang Zhongjing discussed symptoms without neglecting pulses, but unfortunately, people today are ignorant. By studying Master Zhang Zhongjing's *Treatise on Cold Damage* (Shanghan Lun, 《伤寒论》), how could one make errors by initially using Guizhi Tang? Yu Jiayan (Yu Jiayan, 喻嘉言) of Nanchang praised and analyzed Master Zhang Zhongjing's work with profound insight and clear vision, surpassing predecessors, unmatched in recent times. However, where minor discrepancies exist, I venture to debate again, hoping to avoid criticism of error. Thus, from now on, reading *Cold Damage* texts, one need not remain ignorant.