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The disease of latent warmth (Fuwén) erupts along the meridians; this classical instruction is clear and beyond doubt. However, Zhang Shiwang claimed that the eruption of warm pathogenic factors must proceed through the Shaoyang meridian; Lu Jiuzhi asserted that warm-heat diseases must originate in the Yangming meridian; Chen Pingbo held that the lungs and stomach are the sites inevitably invaded by warm pathogens; Wu Ke-you further posited that the Mo-yuan (a location between the interior and exterior) is where epidemic warm pathogens lie latent. Although each school’s discussion has its own insights, they only mention one aspect of warm diseases and cannot generalize the entirety of warm diseases. As for Wu Jutong’s *Wenbing Tiaobian* (Systematic Differentiation of Warm Diseases), he rigidly divided the Sanjiao (Triple Burner: Upper, Middle, Lower), stating that anyone suffering from a warm disease must begin at the Upper Jiao Hand-Taiyin Lung meridian. Consequently, he misidentified seasonal wind-warmth patterns as diseases caused by latent qi erupting into warmth, confusing the two without distinction; this error is particularly egregious. Students should base their studies on ancient classic texts, carefully investigate, and firmly understand that the eruption of warm diseases moves with the meridians. Only then can they possess true insight during clinical practice and avoid confusion by divergent theories.

The pathogen of Cold Damage (Shanghan) transmits from the exterior to the interior; all interior syndromes are invaded by exterior syndromes. The pathogen of warm-heat reaches from the interior to the exterior; all exterior syndromes float outward from interior syndromes. Only the epidemic pathogen originates from the middle pathway of the membrane network (Mo-luo), taking advantage of gaps based on exterior-interior and deficiency-excess conditions to erupt. It does not follow the sequential transmission of meridians, nor can it be exhausted in a single eruption. Wu Ke-you elucidated the "Nine Transmissions" (Jiu Chuan), as well as heat-binding with purgation of surrounding fluid (Rejie Pangliu) and sticky obstruction rather than dry binding; these were his unique insights. Furthermore, Cold Damage sinks from the Qi level into the Blood level, while warm-heat emerges from the Blood level back to the Qi level. Therefore, Cold Damage often begins at the Taiyang meridian, whereas warm-heat often starts at the Yangming meridian or the Shaoyin meridian. This constitutes a clear differentiation between heat returning to the Qi level or the Blood level.

According to the *Suwen·Relun* (Plain Questions: Treatise on Heat): When humans are injured by cold, they develop febrile diseases; even if the fever is severe, death is unlikely. However, those who suffer from "Lianggan Yu Han" (simultaneous contraction of cold affecting both exterior and interior) will inevitably die. It also states: For those who contract Cold Damage and subsequently develop warm diseases, those occurring before the Summer Solstice are called "Wen" (Warmth), and those after are called "Shu" (Summer Heat). It further states: Those whose essence is preserved and stored securely will not suffer from warmth in spring. Initially, there was no concept of contagion. Zhang Zhongjing stated: The *Yinyang Dalun* says: In winter, when the cold is severe, all things hide deeply. If gentlemen maintain their solidity and integrity, they will not be injured by cold; those who encounter it are said to have contracted Cold Damage. The qi of the four seasons can all cause disease, but Cold Damage is considered the most toxic because it forms the most killing and fierce qi. Those who fall ill immediately upon exposure are named "Cold Damage"; those who do not fall ill immediately harbor the cold toxin within the skin and muscles (Sun Simiao described it as within the muscle and bone). By spring, it transforms into a warm disease; by summer, it transforms into a summer heat disease, which is more severe than warmth. Thus, hardworking people often suffer from warm-heat diseases in spring and summer, all caused by encountering cold in winter. It also states: In the eleventh and twelfth months, the cold is already severe, so illnesses contracted then are heavier. Reviewing the discussions in the *Suwen*, Zhang Zhongjing, and various other schools, all state that these are caused by encountering cold toxins in winter, not by sudden contagion.