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The theories regarding latent pathogenic factors (Fu Qi, 伏气), immediate onset upon infection (Ji Bing, 即病), direct invasion (Zhi Zhong, 直中), and transmission through meridians (Chuan Jing, 传经) have been the subject of heated debate. Scholars have focused excessively on textual analysis rather than elucidating actual clinical manifestations. Some argue that immediate onset after cold injury is termed *Shang Han* (Cold Damage, 伤寒), while latent cold transforming into heat after a long period is termed *Wen Bing* (Warm Disease, 温病). Others contend that since the Three Yang meridians are exterior and the Three Yin meridians are interior, how can pathogenic factors fly across to directly invade the Three Yin? Still others state that among *Shang Han* and sudden diseases, cold pathogenic factors are the most toxic and severe in harming humans. Infections during the other three seasons do not necessarily undergo meridian transmission; even if they do, it is not as urgent as in *Shang Han*. "Immediate onset upon invasion" is akin to common colds. Latent pathogenic factors vary in depth: some cold lingers from winter to manifest in spring or summer; some lingers for a month before manifesting the next. All are called latent pathogenic factors, and all involve a distinction between whether they transform into heat or remain cold. How can one simply label latent pathogenic factors as exclusively belonging to Warm Diseases, completely unrelated to Cold Damage? Moreover, in the warm, cool, damp, and hot climates of the three non-winter seasons, the interstices (Cou Li, 腠理) are loose and open, so transmission is slower; whereas in winter cold, interstices are tight, and internal qi is substantial, yet transmission is faster. This reasoning is illogical. Thus, blame is placed on the toxicity of the pathogen, and theories such as "transmission skipping meridians" (Yue Jing Chuan, 越经传) and "erroneous meridian transmission" (Cuo Jing Chuan, 错经传) are fabricated to defend these views. These are mere evasions, stemming from mental obstruction.

I have pondered this: Zhang Zhongjing’s treatises clearly mention wind striking the Six Meridians. If wind can strike directly, why cannot cold? There are two mechanisms for "immediate onset upon invasion": First, injury to the Upper Jiao (Upper Burner, 上焦), which lies in the pathway of ascending yang qi. Injury in the morning leads to disease in the evening, and vice versa. Symptoms begin with aversion to cold followed by fever, termed Taiyang Disease (Taiyang Bing, 太阳病) [Note: Simultaneous fever and aversion to cold indicates "fever and aversion to cold originate from Yang," where Yang refers to the Upper Jiao]. If neglected, various transformations occur, termed meridian transmission. This was stated by predecessors. Second, injury to the Lower Jiao (Lower Burner, 下焦), outside the main pathway of ascending yang qi. Symptoms may include mild aversion to cold without fever, mild fever with severe aversion to cold, or alternating chills and fever without regularity [Note: Absence of high fever with aversion to cold indicates "aversion to cold without fever originates from Yin," where Yin refers to the Lower Jiao]. After two to three days without resolution, the pathogen takes advantage of Taiyang meridian qi to ascend into the neck and back, resulting in high fever [Note: High fever appears at this stage, hence the distinction between "already febrile" and "not yet febrile"], thus forming typical Taiyang Disease. Pathogens may also enter the Shaoyang (Lesser Yang, 少阳) meridian causing alternating chills, fever, irritability, or enter the Yangming (Greater Yang, 阳明) meridian causing constipation and delirious speech. Alternatively, pathogens may directly invade the Three Yin meridians, presenting with predominant symptoms of a specific meridian (e.g., direct invasion of Taiyang with predominant Taiyang signs). Predominant symptoms in any meridian are termed direct invasion. Neglect leads to transformation, termed transmission. Taiyang disease has transmission; direct invasion of Three Yin also has transmission. Thus, Three Yang meridians have interior syndromes, and Three Yin meridians have exterior syndromes. This was mentioned by predecessors but not detailed.

Latent pathogenic factor onset also has two mechanisms: triggering and late onset, detailed in previous chapters. Generally, pathogens linger in the muscles of the Lower Jiao, adhering outside tendons, bones, and blood vessels, avoiding contact with yang qi. Therefore, they often require a significant trigger (such as external pathogenic factors or internal qi shifts) to manifest. The mechanism is severe; treatment may be exterior-releasing or interior-clearing, transforming cold or heat, entirely depending on the strength of the patient's constitution. Pathogens may follow Taiyang qi upward to the neck and back, becoming Taiyang exterior syndrome; or rush directly to the Bladder and Small Intestine, becoming Taiyang interior syndrome. Symptoms include sudden urinary retention and asthma, progressing to edema and jaundice; or directly enter the lower abdomen and Mingmen (Gate of Life, 命门), becoming Shaoyin (Lesser Yin, 少阴) syndrome; or pass through Shaoyin, overflowing into blood vessels, causing chaotic blood flow, becoming Jueyin (Terminal Yin, 厥阴) syndrome. These two scenarios describe patients with deficient lower body qi ("pian si xia xu ren"). Symptoms include diarrhea, cold limbs with curling up but feeling warm internally, sensation of qi rushing to the heart, hardness and distension in both hypochondria, progressing to oral ulcers eroding gums, continuous spontaneous sweating, colic-like pain around the navel, and leakage of five bodily fluids. Alternatively, if Jueyin blood and qi are strong and reject the pathogen, the pathogen moves outward, becoming Shaoyang syndrome. Due to dryness and stagnation in fine blood vessels, the pulse is wiry and thin, symptoms are alternating chills and fever, progressing to urticaria. Or, following the anterior surface of the lower abdomen, ascending to the membranes of the chest and stomach, becoming Yangming syndrome; or following the interior anterior aspect of the lower abdomen, ascending to the diaphragm regions, becoming Taiyin (Greater Yin, 太阴) syndrome. In such cases, although pathogens travel along meridians, they are close to zang-fu organs. Defenses are completely breached, allowing pathogens to go wherever they wish. Loss of righteous qi control leads to rapid transmission. This too was mentioned by predecessors but not detailed.

Zhang Zhongjing’s treatises focus on foot Six Meridian syndromes, while hand Six Meridian syndromes are classified as interior diseases because latent pathogens first manifest in foot meridians and must ascend inward before affecting hand meridians. Furthermore, transmission from Taiyang to Yangming and Shaoyang results in heat syndromes, while Three Yin syndromes result in cold syndromes. This is because when pathogens move outward on the exterior, interior yang becomes trapped and transforms into heat; when pathogens attack directly inward, interior yang drains downward and transforms into cold. If upper jiao cold damage required transmission through all yang meridians before entering yin, Yangming and Shaoyang would already be transformed into heat, and the trapped heat in Three Yin would be even more severe. Why would it suddenly transform into cold? Additionally, in Taiyang disease, headache resolving spontaneously after seven days occurs because the pathogen has exhausted its course within the meridian. If one wishes to prevent progression to the next meridian ("zai jing"), needling the Foot-Yangming meridian prevents transmission and ensures recovery. Old注释 interpreted "exhaustion of the meridian course" as transmission through all six meridians, which later scholars criticized, arguing that "exhaustion of the meridian course" means the pathogen completes its cycle within the same meridian, not transmission. While plausible, this fails to explain the significance of "seven days." In reality, this refers to a scenario where no meridian accepts the pathogen. For example, Taiyang headache: on day two, the pathogen moves to Yangming, but Yangming rejects it; on day three, it moves to Shaoyang, but Shaoyang rejects it; subsequently, it moves to Taiyin, Shaoyin, and Jueyin, but the Three Yin meridians reject it. The pathology remains confined to headache. The pathogen is shallow and easily dispersed, hence spontaneous recovery. "Wishing to progress to the next meridian" implies a heavy pathogen that cannot disperse, with trapped heat seeking to transform into a new disease. Thus, needling Foot-Yangming prevents transmission and vents trapped qi. This is merely one aspect of transmission variation in Taiyang disease and cannot serve as the general rule for Shanghan transmission. These critical junctures have never been fully understood. The root cause is the failure to carefully observe the path of the pathogen and the mechanisms of transformation, using analogies to grasp the actual situation. Instead, scholars cling to isolated phrases from the text to attack each other, failing to apply them to specific clinical contexts. The phrase "not applicable" originates from Yu Shi of Jiashan. Truly insightful words, truly insightful words.