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Heaven has four seasons, and thus there are the Six Excesses (Liu Yin, i.e., Wind, Cold, Summerheat, Dampness, Dryness, and Fire). When humans are affected by these pathogens, disease arises according to the deficiency or excess of their Zang-Fu organs. Pathogens are like thieves breaking into a house; they take advantage of places where walls and doors are not secure to enter.

In the past, three people traveled at dawn in the dew. One remained healthy, one fell ill, and one died. The healthy person had consumed alcohol and food first, resulting in robust Stomach Qi and a solid exterior; the sick person ate but did not drink alcohol; the deceased person walked on an empty stomach. This demonstrates that when pathogens approach, it is because the body's Qi is necessarily deficient.

Spring Qi should be warm, allowing all things to sprout and renew, with its energy being open and unobstructed. If the weather is cold and clothing is thin, causing the Cou Li (pores and interstices) to close, Yang Qi cannot penetrate and vent, leading to various diseases. Sudden onset indicates a light pathogenic invasion; however, some cases involve pathogens acquired from winter. As Wang Shuhe stated: Cold pathogens hide in the skin and muscles, transforming into Warm Diseases (Wen Bing, acute febrile diseases characterized by fever) in spring; such invasions are deep. For poor individuals with dense muscle texture and strong Stomach Qi, who engage in labor and sweat occasionally, even if invaded, the pathogens are expelled through sweat. Thus, although their bodies may be frail, they do not fall ill.

When Cold initially attacks the human body, the skin and hair are affected first, corresponding to the Lung; subsequently, the muscles are affected, corresponding to the Stomach. If one takes acrid-dispersing formulas upon feeling slight discomfort, how could Yang Qi fail to vent and become stagnant to cause disease? Initially, there is body heat and cough; severely, rashes or macules appear. This is collectively named "Spring Yang Cold Stagnation." There are also cases where pathogens are acquired in spring, Yang Qi fails to penetrate, and due to the individual's strong constitution, symptoms do not appear immediately. Instead, as late spring approaches early summer, the desire to vent arises, leading to febrile illness. These pathogens mostly transmit to the Pericardium and Stomach, presenting as alternating chills and fever, persistent fever, rashes, macules, or epidemic warm diseases (Wen Yi, warm diseases with contagious nature), named "Late-Onset Spring Warmth."

Summer corresponds to the virtue of Fire, and all things flourish. However, south of the Yangtze River, the land is low and influenced by tides. During the continuous plum rains, Dampness pathogens are prevalent; during Major and Minor Heat periods, intense heat prevails. Summerheat damages Human Qi, and Dampness invades the intestines and stomach. In summer, one should be cautious in daily routine and consume bland flavors, which are essential for health preservation. Summerheat is formless and enters through the mouth and nose; it first injures the Qi level, causing shortness of breath, soft pulse, and limb weakness. Summerheat injures the Heart; since the Heart governs fluids, it causes mental restlessness, insomnia, and sweating. Alternatively, after long sunny days making the soil dry, sudden heavy rain causes heat vapor to rise, making one susceptible to Summerheat. Whether traveling or resting in simple shelters, despite differences in labor and rest, the susceptibility to pathogens is the same; this is called "Yang Summerheat." Conversely, residing in cool pavilions or water terraces, loving cooling, and preferring frozen beverages depresses Stomach Qi, causing aversion to cold, high fever, scanty sweat, sluggish deep pulse, vomiting, or diarrhea; this is called "Yin Summerheat," which must be understood. Summerheat invariably carries Dampness and filth. Some diseases manifest as Cholera (Huo Luan, acute gastroenteritis with vomiting and diarrhea), having four causes: contracting Summerheat, catching Cold, contracting Dampness, and dietary injury. Red and white dysentery results from internal invasion of Damp-Heat and irregular diet, named "Simultaneous Disease of Summerheat and Dampness."

Autumn Qi should be cool, and Metal Qi is clear and肃 (solemn/clear), so fewer people fall ill. If autumn sun is scorching, humans contract its Qi, or if they sit outdoors seeking coolness, pores are obstructed by wind and dew, preventing pathogen expulsion, making them highly susceptible to disease. Malaria (Nue Zheng, a parasitic disease with alternating chills and fever) largely originates here. Symptoms include body heat, headache, cough, and wheezing; the later the onset, the heavier the condition, named "Cool Wind Attacking Summerheat."

Winter Qi is biting, and all things hibernate. However, latent Summerheat from summer and autumn remains inside. At Winter Solstice, when Yang Qi begins to recover, sensing this Qi leads to venting, often presenting as aversion to cold with hot limbs, cough, hemoptysis, bleeding gums, and epistaxis. Additionally, mild winter weather with insufficient concealment of Yang Qi leads to Winter Warmth (Dong Wen) syndrome. During the three winter months, those skilled in health preservation avoid fog and dew in the morning, stay indoors alone, and sleep without excessive warmth, establishing the root for spring vitality. Walking on an empty stomach at dawn and failing to regulate sexual activity easily generates Cold diseases, historically named Shang Han (Cold Damage, a general term for exogenous febrile diseases). Can one not be cautious? This is named "Failure of Winter Storage." The treatment methods were fully prepared by former sages; why add my words? However, no one had established laws specifically divided by four seasons. Therefore, I explored the subtleties and presented my own views to compile this section. May practitioners understand it clearly; by studying it thoroughly, they will naturally achieve mastery. Conditions unrelated to atmospheric influence should be classified separately to show my intent. The *Nei Jing* discusses seasonal pathogenic influences based on the Four Qi; my division of seasonal illnesses and treatments traces the root and source. It differs little from ancient legislation, except for the different primary herbs used.