The method of Six-Meridian differentiation in Zhang Zhongjing's work does not fully align with the discussions in the *Huangdi Neijing* (Yellow Emperor's Inner Canon). I once pondered this deeply but could not find an explanation. It was only after reading Cheng Jiaoqian's (Cheng Zhi) *Shanghan Hou Tiaobian* (Differentiation of Post-Strain Cold Sequelae) that I encountered a passage refuting Wang Shuhe's "Preface to the Examples," which offered profound and logical analysis, highly worthy of adoption.

The *Neijing* states: "All heat diseases belong to the category of cold damage." The use of the word "category" indicates that heat disease is merely one type within cold damage. However, they are both similar and dissimilar; they resemble each other yet do not. Although both involve the Six Meridians, the etiological factors of cold and heat differ.

For instance, on the first day, the Taiyang Meridian (Greater Yang Meridian) is affected, presenting with headache, stiffness of the neck and back, and rigidity of the waist and spine; this is similar. The dissimilarity lies in the presence or absence of aversion to cold. On the second day, the Yangming Meridian (Yang Brightness Meridian) is affected, presenting with fever, eye pain, dry nose, and insomnia; this is also similar. The dissimilarity lies in the fact that in cold damage, the pathogen enters the Stomach, whereas in heat disease, it does not enter the Stomach, because entering the Stomach prevents further transmission to other meridians. On the third day, the Shaoyang Meridian (Lesser Yang Meridian) is affected, presenting with hypochondriac pain and deafness; this is similar. The dissimilarity lies in the fact that cold damage presents with alternating chills and fever, while heat disease presents only with heat in the interior half (half-li), without cold in the exterior half (half-biao).

In the Three Yin syndromes of cold damage, there is a complex mixture of cold and heat, varying irregularly; whereas in heat disease, there is only heat and no cold. On the fourth day, the Taiyin Meridian (Great Yin Meridian) is affected, presenting with abdominal fullness and dry throat; this is completely dissimilar. The Taiyin syndrome of cold damage involves abdominal fullness, vomiting, diarrhea, and inability to eat. On the fifth day, the Shaoyin Meridian (Lesser Yin Meridian) is affected, presenting with dry mouth, dry tongue, and thirst; although this resembles one aspect of Shaoyin cold damage where the pulse is faint and fine and the patient desires sleep, overall it remains dissimilar. On the sixth day, the Jueyin Meridian (Terminal Yin Meridian) is affected, presenting with vexation, fullness, and retraction of the testicles; while vexation may occur in cold damage, overall it is dissimilar. The Jueyin syndrome of cold damage involves inability to eat and vomiting roundworms immediately after eating.

Such detailed and precise analysis can be called a unique insight through the ages. I would further argue that the *Neijing*'s mention of days serves to inform people of the constant patterns, while Zhang Zhongjing's omission of days aims to teach people to understand variations. Those studying cold damage must first break through this confusion to gain mastery over Zhang Zhongjing's methods.

Zhang Zhongjing's book is named *Shanghan Lun* (Treatise on Cold Damage), yet it lists Wind Strike (Zhong Feng) at the beginning. The *Neijing* states: "Wind is the beginning of all diseases." If the body remains calm and pure, the muscle pores (Cou Li) will close and resist external pathogens; even severe wind toxins cannot harm it. Thus, Wind Strike often arises from loose Cou Li, allowing wind pathogens to easily invade. Therefore, the *Benlun* (Original Treatise) states: "Taiyang Wind Strike, with floating Yang and weak Yin. Floating Yang causes spontaneous heat; weak Yin causes spontaneous sweating. With shivering aversion to cold, chilly aversion to wind, mild fever, nasal congestion, and dry retching, Guizhi Tang (Cinnamon Twig Decoction) should govern it." The described symptoms of Taiyang Wind Strike are all characterized based on the skin and hair level. Since the pathogen enters from the exterior, it must be driven out urgently. However, since the Cou Li are inherently loose, excessive sweating should not be induced. Therefore, the rationale for using Guizhi Tang by Zhang Zhongjing is primarily to harmonize Ying (Nutritive Qi) and Wei (Defensive Qi) to release the muscle layer. It seeks a slight perspiration, not profuse sweating like flowing water. In the formula, Shaoyao (Paeoniae Radix Alba), Gancao (Glycyrrhizae Radix), and Dazao (Jujubae Fructus) mainly secure Ying Qi to push out Wei pathogens, preventing wind pathogens from invading internally and facilitating their exit. Then, Guizhi (Cinnamomi Ramulus) combined with Shengjiang (Zingiberis Rhizoma Recens) establishes continuous power to expel pathogens. Modern practitioners who fail to understand this principle often replace it with a batch of wind-dispelling herbs, forcing sweat, or even adding acrid-hot drugs, disturbing Ying and Blood. Rarely do such cases avoid causing adverse changes leading to critical conditions. Should not physicians exercise caution at the outset?