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The *Classic of Internal Medicine* states: "In winter, one is injured by cold." This refers to the invasion of cold pathogenic factors into the human body after the solar term of Start of Winter. If the body's righteous qi is solid and dense, what harm can there be? However, if one is even slightly negligent, the cold will injure the meridians associated with water (i.e., the Foot Shaoyin Kidney meridian), immediately presenting with alternating chills and fever, absence of sweating, and a floating and tight pulse; this is named Cold Damage (Shanghan).

Once spring arrives, it can no longer be termed Cold Damage. Nevertheless, contracting cold in winter has distinctions of depth: deep contraction is called "Zhong Han" (Mid-Cold), while shallow contraction is called "Mao Han" (Covered-Cold). Zhong Han occurs when cold pathogens directly invade the interior of the Three Yin meridians (Taiyin, Shaoyin, Jueyin), thus manifesting as vomiting, diarrhea, and abdominal pain; it urgently requires hot-natured decoctions to dispel cold. Mao Han occurs when cold pathogens cover the exterior of the body shell, manifesting as aversion to cold, fever, and body ache, which is not difficult to cure through diaphoresis (sweating). The above briefly outlines the general concepts of Cold Damage, Mid-Cold, and Covered-Cold. Additionally, there is the syndrome of Winter-Warmth (Dong Wen), which must be detailed. Winter-Warmth refers to a situation where winter should be cold but is instead warm; non-seasonal qi prevails, and upon exposure, illness ensues immediately. One should employ acrid-cool methods; strictly avoid misusing Mahuang Tang (Ephedra Decoction), Guizhi Tang (Cinnamon Twig Decoction), or Da Qinglong Tang (Major Green Dragon Decoction). Misuse will inevitably lead to myriad transformation syndromes.

These four conditions represent new acquisitions contracted during winter that manifest immediately. Conversely, if one contracts slight cold or warmth, which does not manifest at the time but waits until the following spring to erupt, this constitutes a latent Qi disease (Fu Qi Bing), which must be treated according to various categories of Warm Diseases.

A questioner asked: "I have seen in Dongyuan’s [Li Dongyuan] works discussions such as 'Winter injury by cold leads to warmth diseases in spring.' Have you merely picked up the dregs of predecessors' spittle, yet claiming it as an innovative breakthrough? Are you deceiving others, or are you severely deceiving yourself?" I replied: "Your words are excessive! I too have seen the book *Ci Shi Nan Zhi* (Difficulties of This Matter), which contains four treatises discussing the principles of excess and deficiency in the generation and restriction cycles of the Five Elements, and the relationships of being overcome and overcoming. Their meanings are obscure, making it indeed a difficult book to understand. I now divide the discussion into eight chapters to serve as an outline for seasonal syndromes. The logic is thorough, making it easy for readers to comprehend. I clearly distinguish the syndromes presented by new acquisition from winter cold injury; and the syndromes presented by latent qi from winter cold injury leading to spring warmth disease, detailing them one by one with clarity like seeing the palm of one's hand. This differs significantly in meaning from Dongyuan’s discussion. How could I possibly pick up his dregs and claim them as my own? It is akin to taking an examination with the same topic, yet the essays are substantially different. How dare I claim to deceive others and myself? Is this not so?"