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Li Dongyuan stated: Fever in the four limbs, or dryness of the mouth, tongue, and throat, occurs because heat arises from the Heart and Small Intestine. The pathogenic fire attacks the main position, resulting in a combination of damp-heat, which causes restlessness and confusion.

The four limbs belong to Spleen Earth; when Fire attacks them, fever in the four limbs results. Alternatively, heaviness of the body and wandering pain occur because damp-heat struggles with each other, and wind-heat is constrained and unable to extend freely.

Respectfully noted: Various diseases presenting with exterior heat may have similar symptoms, but their pulse qualities and pathological origins differ. Therefore, categorizing the above examples: Zhang Zhongjing discussed cold damage (Shanghan) and acute febrile diseases. Fever accompanied by aversion to cold indicates onset in the Yang aspect; a floating, tight, and choppy pulse indicates Wind-Cold lodging in the Ying (Nutrient) and Wei (Defensive) levels. He divided the transmission into Six Channels, detailing over two hundred pulse-syndrome patterns, including those caused by mismanagement and complications, as well as warm malaria, wind-warmth, and warm epidemics. These are all variations arising from winter cold injury manifesting later as various pulse-syndrome changes, which is why the *Treatise on Cold Damage* (*Shanghan Lun*) was written. Liu Wansu (Liu Shouzhen) discussed heat diseases, attributing them to the constraint of Yang Qi generating heat, or severe constraint causing aversion to cold. This refers to "Excess leads to harm, restraint brings regulation," where extreme Yang resembles Yin. These resemble cold damage, which is why the *Book on Original Disease Patterns* (*Yuanbing Shi*) was written. Li Dongyuan (Li Mingzhi) discussed internal injury to the Spleen and Stomach. Initially, there is often shortness of breath with panting, fever, and irritability; the pulse is large and forceful with headache or unceasing thirst. The skin cannot withstand wind and cold, leading to alternating chills and fever, which closely resembles exterior cold damage. This is why the *Treatise on the Spleen and Stomach* (*Piwei Lun*) was written. The theories of these three gentlemen fundamentally aim to elucidate the principles of disease mechanisms in the *Inner Canon* (*Neijing*), systematically distinguishing the root and branch of heat syndromes, preventing one from mistaking one for another. However, scholars who fail to examine the underlying principles become specialized in narrow fields. Thus, Master Zhu Danxi said: Those who study Zhang Zhongjing first focus on cold damage, fearing the mistake of treating internal injury as exterior excess; those who study Li Dongyuan first focus on Stomach Qi, fearing the mistake of treating exterior excess as internal injury; those who study Liu Wansu first focus on heat, fearing the mistake of treating cold as heat. It is better to prioritize the *Inner Canon*, which naturally becomes flexible and vibrant, as its principles are profound and comprehensive. Without the treatises of these three gentlemen, how would one understand the accumulated obscurities of the classics? Yet, those who fail to examine principles and become narrowly specialized mistake one for another, misleading many people. Alas, Zhu Danxi's insights are subtle. Observing Zhang Zhongjing's methods, treatment relies on pulse verification, allowing infinite variation, deeply aligning with the *Inner Canon*. For example, if cold pathogen is at the exterior, use acrid-warm herbs to induce sweating; if in the interior, use acrid-hot herbs to warm; if transmitted to the half-exterior/half-interior level, use sweet-cold herbs to harmonize; if transmitted deep into the interior, use bitter-cold herbs to purge. Cooling agents are not abandoned either. Generally, one must rely on pulse verification to achieve flexibility, rather than adhering rigidly to fixed theories or specific formulas. Moreover, human diseases present subtle signs of Water and Fire. As Wang Bing (Wai Tai Pu) stated: "Heat comes and goes, appears by day and hides by night, emerges by night and hides by day, moving with seasons—this is absence of Fire." This example aligns with Liu Wansu's discussion on "Excess leads to harm, restraint brings regulation" in the *Book on Disease Patterns*. Zhu Danxi further discussed Yin-Yang, stating that aversion to cold does not necessarily mean cold, and aversion to heat does not necessarily mean heat, because the signs of Water and Fire in the human body are obscure and unpredictable. The ancients' deductions were thorough. However, Zhang Zhongjing's pulse methodology for cold damage also cited miscellaneous diseases; Liu Wansu's pulse methodology for heat syndromes was not exhaustive. Scholars should base themselves on Zhang Zhongjing, reference He Suo's pulse methods, and distinguish between internal injury and exterior excess. As Wang Haizang said: Zhang Zhongjing considers wiry and choppy pulses as Yin, while He Suo considers them as Yang. Although there is a distinction between Yin and Yang, they do not depart from the principle that numerous pulses indicate heat, and slow pulses indicate cold. Zhang Zhongjing and He Suo approached from different paths but did not contradict each other; combined, both are correct. Zhang Zhongjing's discussion on cold damage posits that pathogens enter from the exterior via Qi, considering the wiry pulse as a Yin pathogen entering from outside, affecting the Taiyang channel first. He Suo's discussion on miscellaneous diseases posits that pathology originates internally from Blood, considering the wiry pulse as a Yang disease originating inside, affecting the Shaoyang channel first. In this way, although clinical manifestations may be similar, the pulse quality and pathological origin differ. If scholars examine this carefully, they will naturally adapt and avoid mistaking one condition for another or being confined to rigid theories and specific formulas.