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According to the *Nan Jing* (Classic of Difficult Issues): The pulse of warm disease circulates through the various meridians. If it is unknown which meridian is affected, treatment should be directed according to the location of the affected meridian.

If there are symptoms of the Taiyang syndrome (Taiyang Meridian Syndrome), such as headache and aversion to cold, and after sweating or purging therapies, the condition persists beyond the transmission cycle of one meridian, and the pulse at both the cun (inch) and chi (cubit) positions is floating, this is Warm Disease of the Taiyang channel.

If the disease manifests after the appropriate season has passed, the pathogen is not in the exterior. Since sweating or purging therapies have already been applied, the pathogen is also not in the exterior. The classics state: "Those who do not have aversion to cold but instead have thirst suffer from warm disease." This clearly indicates that the heat originates internally and reaches the exterior, proving the absence of exterior syndrome evidence.

Commentary: In cold damage (Shanghan), the transmission of disease proceeds from the fu organs to the zang organs, and from yang meridians to yin meridians. Warm disease does not follow this pattern of transmission; it affects only one or two meridians. It may be due to the fire pathogen of a specific meridian, or because the pathogen takes advantage of deficiency in a specific meridian. Being struck by cold qi in spring, the pathogen emerges from the interior to the exterior, causing symptoms such as alternating chills and fever. If it strikes the fu organs, it causes fu organ disease; if it strikes the zang organs, it causes zang organ disease. Regardless of the number of days elapsed, it remains confined to these one or two meridians. The *Nei Jing* (Inner Canon) states that one should observe which meridian is disturbed and treat accordingly; this is a clear verdict. Jie'an's method of differentiating diseases by meridian is correct. However, defining warm disease as "passing the Taiyang meridian without transmitting to other meridians" is a key principle for distinguishing between cold damage and warm disease, which deserves admiration.

Discussion: Is there aversion to cold? Answer: Cold damage arises from wind-cold in winter, presenting with external symptoms of aversion to cold and aversion to wind. Since it is named warm disease, these symptoms should be absent. Question: On what basis do you say this? Answer: Based on the classics. The classics state: "In Taiyang disease, if there is fever but no aversion to cold, accompanied by thirst, it is warm disease." No aversion to cold indicates the disease is not caused by external invasion; thirst clearly indicates heat reaching the surface from the interior.

Commentary: Winter cold damage presents with aversion to cold due to external invasion, which is correct. However, stating that warm disease never presents with aversion to cold is incorrect. Generally, warm disease occurs when yang qi is freely circulating but is constrained by spring wind-cold. Although it involves internal heat, it is also triggered by external factors, thus presenting with symptoms like aversion to cold. Does only summerheat present with this symptom? Summerheat disease also presents this way. Summerheat is an external fire pathogen injuring the zang-fu organs, causing intense heat inside and out. Extreme heat can lead to shivering, manifesting as aversion to cold. If physicians do not understand this, they may misdiagnose it as cold damage; careful differentiation is essential.

Discussion: Both summerheat injury and cold damage involve fever. Misdiagnosing summerheat as cold damage is inadvisable. Generally, cold damages the form (body structure), while heat damages qi. In cold damage, external cold invasion results in a floating and tight pulse. In summerheat injury, there is no aversion to cold, and the pulse is deficient/weak. This is the distinction. The classics state: "Pulse is full/excessive with body cold indicates cold damage; pulse is weak with body heat indicates summerheat injury." Treatment should use Xiao Chai Hu Tang (Minor Bupleurum Decoction). If thirsty, add Shigao (Gypsum Fibrosum) and Zhimu (Anemarrhenae Rhizoma), or use Renshen Baihu Tang (Ginseng White Tiger Decoction). If prolonged rain causes excessive dampness, use Cangzhu Baihu Tang (Atractylodis Rhizoma White Tiger Decoction). If the vital qi is inherently weak and the injury is severe, use Qingshu Yiqi Tang (Clear Summerheat and Boost Qi Decoction).

The term "cold damage" generally refers to the severe cold of winter, where water freezes and ice forms, creating a killing/cruel qi. When people are exposed to it and fall ill immediately, it is called cold damage, characterized by aversion to cold, headache, and fever. Therefore, Mahuang Tang (Ephedra Decoction) or Guizhi Tang (Cinnamon Twig Decoction) are used to disperse exterior cold pathogens, naturally resolving fever and cooling the body. Are there any complications? If headache and aversion to cold (exterior signs) are resolved, but delirium, fear of heat, restlessness, thirst, and constipation appear, purgation therapy should be used. If stool becomes unblocked but heat worsens, what strange complication is this? In spring, summer, and autumn, even if there is aversion to cold, fever, and mild headache, it is considered a common cold (ganmao), a mild case of non-seasonal sudden cold, not as severe as true winter cold damage. If cold is contracted in winter but does not manifest immediately, it lies latent in the skin and muscles. In spring, summer, or autumn, this latent cold transforms into warm disease or heat disease depending on the seasonal qi. Because warm or summerheat conditions are about to emerge, exposure to sudden cold triggers the transformation into warm disease in spring. Once transformed, it cannot be referred to as cold again. Thus, Zhang Zhongjing stated: "Fever without aversion to cold and with thirst indicates warm disease." Summerheat disease is similar; compared to warm disease, it involves more intense heat without aversion to cold, indicating the pathogen is not external, and thirst indicates heat originating internally and reaching the exterior, confirming no exterior syndrome. Treatment for warm and summerheat diseases generally prohibits sweating therapy, especially if onset is delayed, as the pathogen is no longer in the exterior. Latent cold transforming into summerheat in summer is essentially heat disease. The term "summerheat" is derived from the dominance of summer fire qi. Since warm and heat syndromes originate from latent winter cold, they are collectively termed cold damage. However, since the time of onset differs, treatments must not be confused. Claiming all four seasons involve true cold damage is incorrect. These three categories (warm, heat, summerheat) should be treated with acrid-cool agents. Using winter cold damage medications universally would be fatal. Xinqiang Huozhe Tang (Acrid Cool Notopterygium and Heteromorpha Decoction) is suitable; it can also substitute Da Qinglong Tang (Major Green Dragon Decoction) for treating cold damage complicated by wind or wind-cold injury, providing stability. One formula replaces three dangerous ones. Such efficacy is miraculous! The layperson is unaware of this. If the exterior is resolved but interior signs remain, purgation is appropriate without doubt. Furthermore, if cold damage persists after purging beyond the transmission cycle, it becomes warm disease. Having undergone sweating or purging, the pathogen is no longer in the exterior; treatment must adapt to the specific condition. For individuals engaged in hard labor, symptoms of headache, aversion to cold, fever, soreness in bones and legs, slight thirst, spontaneous sweating, and a floating, large but weak pulse indicate cold injury due to labor. Bu Zhong Yi Qi Tang (Tonify the Middle and Augment the Qi Decoction), an acrid-warm formula, is beneficial. The classics state: "Warmth can remove great heat," referring to this scenario. For cases requiring harmonization, modify Xiao Chai Hu Tang. If purgation indications appear, add Dahuang (Rhei Radix et Rhizoma) to gently promote bowel movement. Avoid overly harsh medicines, as the harm is significant. If initial symptoms lack fever and headache, but present with aversion to cold, cold limbs, abdominal pain, vomiting, diarrhea, and a deep, slow, weak pulse, this is direct transmission of cold (zhizhong han zheng). It requires warming therapy, not sweating or purging. Epidemic pestilence (yili) is caused by abnormal seasonal qi, affecting old and young similarly through contagion. Avoiding foul odors prevents damage to true qi; exposure damages righteous qi, leading to contagion. Just as a strong wall keeps thieves out, strong righteous qi repels pathogens; when righteous qi is weak, pathogens enter opportunistically. Treatment differs from warm/summerheat. With exterior signs, use Renshen Baidu San (Ginseng Detoxification Powder); with half-exterior/half-interior signs, use Xiao Chai Hu Tang; with full interior signs, use Da Chai Hu Tang (Major Bupleurum Decoction) for purgation. Without pulse diagnosis, aim for balance. Malaria and dysentery are also epidemics; treat them according to standard methods.

Commentary: Differentiating cold damage from summerheat injury is crucial. It is like a boat saving lives; those who read and understand it clearly should study it carefully to grasp its essence and apply it judiciously.