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Zhang Zhongjing's *Treatise on Cold Pathogenic Diseases* (*Shanghan Lun*) is a work that comprehensively governs the treatment of exogenous diseases, rather than being exclusively for treating wind-cold pathogens. The differentiation of the Six Channels (Liu Jing) is clear and distinct; thus, the patterns of cold diseases, warm diseases, and epidemics are all made evident. The following outlines are recorded here: "The characteristic of Taiyang disease (disease of the Taiyang channel) is a floating pulse, headache, stiffness of the neck, and aversion to cold." "The characteristic of Yangming disease (disease of the Yangming channel or fu-organ excess heat) is 'stomach-house excess' (gastric-intestinal dryness-heat accumulation)." "The characteristic of Shaoyang disease (disease of the Shaoyang channel) is bitter taste in the mouth, dry throat, vertigo, and deafness." "The characteristic of Taiyin disease (deficiency-cold disease of the Taiyin spleen channel) is abdominal pain, spontaneous diarrhea, and frequent vomiting." "The characteristic of Shaoyin disease (deficiency disease of the Shaoyin heart-kidney) is merely desiring sleep (mental lethargy)." "The characteristic of Jueyin disease (mixed cold-heat disease of the Jueyin liver channel) is excessive thirst, qi rushing up to the chest, hunger without desire to eat, vomiting roundworms after eating, and if purgatives are misused, diarrhea will not cease."

Regardless of whether it is an exogenous or endogenous disease, regardless of its manifestation, nothing surpasses these six characters: Exterior (Biao), Interior (Li), Cold (Han), Heat (Re), Deficiency (Xu), and Excess (Shi). The Three Yang channels belong to the Exterior, and the Three Yin channels belong to the Interior. The Interior within the Exterior refers to Yangming; the Exterior within the Interior refers to Shaoyin. They each have a mutual exterior-interior relationship. The Fu organs of the Three Yang govern the Exterior, while their Jing channels govern the Interior. For the Three Yin channels, the Heart and Lung govern the Exterior, while the Spleen, Liver, and Kidney govern the Interior. For exogenous diseases, Exterior patterns are suitable for diaphoresis (sweating method), and Interior patterns are suitable for purgation. For endogenous injuries, Exterior patterns are suitable for clearing and tonifying, while Interior patterns are suitable for warming and tonifying. Endogenous injury leading to yang deficiency results in yin excess; those with yin excess are prone to contracting cold pathogens. Endogenous injury leading to yin deficiency results in yang hyperactivity; those with yang hyperactivity are prone to contracting heat pathogens. This is what is meant by "pathogens entering due to deficiency." Here, "deficiency" refers to the weakness of healthy qi, and "excess" refers to the abundance of pathogenic factors. Thus, the classics state: "When pathogenic factors are abundant, it is an Excess pattern; when essence and qi are depleted, it is a Deficiency pattern." If physicians can comprehend and intricately analyze these principles, distinguishing them clearly and logically, they will be sufficiently competent.

Wind
Wind pathogens have internal and external origins. Internal wind pathology affects the Liver; treatment should employ acrid-cool methods. External wind pathology affects the Lungs; treatment should employ warm-dispersing methods. Accompanied by cold, the pulse is tight; accompanied by dampness, the pulse is wiry; transforming into dryness, the pulse is rapid; transforming into cold, the pulse is slow; the primary disease presents with a floating pulse.

Cold
Cold pathogens have Exterior and Interior aspects, each having Deficiency and Excess types. In Excess cases, resolve the Exterior using Mahuang Tang (Ephedra Decoction); attack the Interior using Sanwu Baisan (Three-Ingredient White Powder). In Deficiency cases, consolidate the Exterior using Guizhi Tang (Cinnamon Twig Decoction); warm the Interior using Sini Tang (Frigid Extremities Decoction). Accompanied by wind, the pulse is floating; accompanied by dampness, the pulse is deep.

Summerheat
Hot weather and humid ground combine to form a syndrome. Summerheat is prevalent according to the season, hence named accordingly. When pathogenic factors are excess, the pulse is surging; when healthy qi is deficient, the pulse is soggy.

Dampness
Dampness has Clear and Turbid distinctions. Dew-like dampness injuring the Qi level is called Clear dampness; tide-like dampness injuring the Blood level is called Turbid dampness. Clear dampness is suitable for diaphoresis; Turbid dampness is suitable for promoting urination. Transforming into dryness, the pulse is urgent; transforming into cold, the pulse is slow; the primary disease presents with a slippery pulse.

Dryness
Dryness has Deficiency and Excess types. Deficient dryness rescues the Lungs; Excess dryness drains the Heart. Using sour-sweet cool-moistening methods constitutes the standard correct treatment. Pathogenic excess presents with a choppy pulse; healthy qi deficiency presents with a short pulse.

Fire
Fire pathogens have Yin and Yang distinctions. Yang fire can be treated by "drawing firewood from under the cauldron" (clearing heat and draining fire); Yin fire is suitable for "guiding the dragon back to the sea" (nourishing yin and descending fire). Yang fire presents with a forceful pulse; Yin fire presents with a pulse lacking spirit.