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In winter, cold pathogenic factors invade from the skin and hair, moving from the exterior to the interior. Initially, symptoms of the Three Yang meridians appear, such as Taiyang disease (disease syndrome caused by pathogenic invasion of the Taiyang meridian), characterized by stiffness and pain in the head and neck accompanied by aversion to cold. If the disorders of the Three Yang meridians are not resolved, the pathogen gradually transmits into the Three Yin meridians. Among these, some pathogens remain in the Three Yang meridians without entering the Three Yin; some knot in the Fu organs of the Stomach without involving other meridians; and some directly strike the Three Yin meridians without passing through the Three Yang. All these Shanghan (Cold Damage) syndromes initially present with signs of cold pathogenic factors. Only after onset do they gradually transform into heat and transmit inward, revealing heat signs. Therefore, the initial treatment must focus on unblocking Yang and dispelling cold. Only after transformation into heat is there a method to drain heat. This is the general principle of Shanghan disease.

As for Warm diseases (Wenbing), they arise from cold pathogenic factors latent in Shaoyin (the Kidney meridian system) during winter. When Yang Qi moves internally in spring and summer, the latent pathogen transforms into heat and emerges outward from Shaoyin. If the pathogen emerges via the Taiyang meridian, it also presents Taiyang meridian symptoms, such as stiffness and pain in the head and neck, similar to Shanghan. However, Shanghan lacks internal stagnant heat, so there is aversion to cold without thirst, clear urine, and no internal heat. In contrast, Warm pathogens manifest superficially while heat stagnates internally; although exterior symptoms exist, internal heat is already vigorous. Symptoms include thirst, yellow urine, heat in the Chi pulse area (wrist), and joint pain—various signs of internal heat absent in Shanghan. The same applies when symptoms involve Yangming disease (syndrome of the Yangming meridian) or Shaoyang disease (syndrome of the Shaoyang meridian). Initial treatment focuses on clearing and draining internal heat and guiding the pathogen outward. This contrasts with Shanghan treatment, which uses warming versus cooling methods. Cold contracted and immediately manifesting is Shanghan, progressing from exterior to interior; cold pathogen stagnating and transforming into heat manifests as Warm disease, progressing from interior steaming outward. Shanghan initially never shows internal heat signs; Warm disease always presents internal heat signs at onset. This is the key distinction in differentiating Shanghan and Warm diseases for medication. Understanding this allows for clear clinical reasoning.

Latent pathogens from winter, stagnating until spring and summer, activate with internal Yang Qi, transforming into heat and emerging outward; this is Warm disease caused by latent Qi (Fuqi). The *Neijing* states: "Winter injury by cold leads to Warm disease in spring." It also says: "For those whose Shanghan transforms into Warm disease, onset before the Summer Solstice is termed Warm disease, and after the Summer Solstice is termed Heat disease (Shu)." The *Nanjing* states that Shanghan includes five types, among them Warm disease and Heat disease. The *Shanghan Lun* states: "Taiyang disease with fever, thirst, and no aversion to cold is called Warm disease." All these refer to Warm disease caused by latent pathogens.

Another type is Wind-Warmth (Fengwen) pathogen. Contracted during spring and summer from warm winds, the pathogen stagnates in the Lung, causing cough and fever, potentially developing into macules (Shazhen). The *Neijing*'s statement "Wind rampant within, treat with acrid-cool" and Ye Tianshi's *Wenre Lun* statement "Warm pathogens enter from above, first attacking the Lung" both refer to this acute contraction of Wind-Warmth. Latent Qi emerges from within; treatment focuses on clearing and draining internal heat. Its manifestations are complex, requiring observation of Six Meridian (Taiyang, Yangming, Shaoyang, Taiyin, Shaoyin, Jueyin) patterns to establish random legislation. Acute Wind-Warmth targets the Lung specifically; treatment focuses on acrid-cool dispersal. For severe heat, sweet-cool resolving methods are added. The path of interior-exterior interaction differs significantly from latent Warm disease; the depth and weight of treatment are also distinct. Recent physicians exclusively follow Ye Tianshi, ignoring latent Qi-induced Warm disease. Upon encountering Warm pathogens, whether acute or latent, they uniformly apply Ye's light acrid-cool methods, prescribing Yinqiao San (Honeysuckle and Forsythia Decoction) or Sangju Yin (Mulberry Leaf and Chrysanthemum Decoction) casually. Physicians and patients prefer this simplicity. Those proposing latent Qi theories are dismissed as heterodox, ignorant of what latent Qi disease entails. Alas! Latent Warm disease is common among external contractions, especially in the South, not a strange ailment. It is recorded in the *Neijing*, *Nanjing*, and *Shanghan Lun*, not heterodoxy. Clinicians' inability to distinguish it, lacking even basic pathways, renders medical practice questionable!