Regarding the Six Qi (Wind, Cold, Summer Heat, Dampness, Dryness, Fire), their numerical sequence begins from Heaven and ends on Earth. In the first half of the year, starting after the Great Cold solar term, the Heavenly Qi dominates; in the second half of the year, starting after the Great Heat solar term, the Earthly Qi dominates; the interaction between Heaven and Earth is governed by the "Qi Jiao" (the intersection of Heavenly and Earthly Qi). When the ruling Qi is Hot, one should not use Hot remedies to avoid offending it; when the ruling Qi is Cold, one should not use Cold remedies; when the ruling Qi is Cool, one should not use Cool remedies; when the ruling Qi is Warm, one should not use Warm remedies. If the ruling Qi matches the Principal Qi, one should also not offend it; if it differs, one should offend it only slightly. This is referred to as the "Four Feared Things." However, if the Heavenly Qi contradicts the seasonal norm, one may follow the actual season and the factors overcoming the Principal Qi, allowing for appropriate intervention, aiming for balance without excess.

The so-called Epidemic Diseases are caused by abnormal Qi present in all four seasons. In spring and summer, there may be times of cold and chill; in autumn and winter, there may be times of warmth and heat. Within a certain region, if people of all ages suffer from similar symptoms, this is called "Tian Xing" (Heavenly Transmission/Contagious Disease). If spring should be warm but is restrained by Clear/Cold Qi, the pathogenic factor is attributed to the Liver, and the disease is named "Qing Jin Qian" (Green Tendon Pulling); if summer should be hot but is restrained by Cold Qi, the pathogenic factor is attributed to the Heart, and the disease is named "Chi Mai KT" (Red Vessel [Condition]); if autumn should be cool but is suppressed by Hot Qi, the pathogenic factor is attributed to the Lung, and the disease is named "Bai Qi Li" (White Qi Fox-like); if winter should be cold but is suppressed by Warm Qi, the pathogenic factor is attributed to the Kidney, and the disease is named "Hei Gu Wen" (Black Bone Warmth); Earth has no fixed form and is named due to Fire, thus varying with Metal, Wood, Water, and Fire, and the disease is named "Huang Rou Sui" (Yellow Flesh Following). Such Tian Xing diseases, if severe, spread poison throughout the world; if moderate, they affect one region or village; if minor, they concentrate on one family. All are summoned by the collective conduct of the common people. Therefore, the spirits of Heaven and Earth utilize this abnormal Qi to inflict punishment. Moreover, human fate involves different encounters, and fortune varies between smooth and obstructed periods, hence some diseases concentrate on a single family. Since Heaven and Earth generate such harmful Qi, they also provide things born from Heaven and Earth to guard against it, which is called "Xian Ren Zhi Fang" (The Wise Know the Method).

Patients exhibit fever, lower back pain with stiffness and urgency, legs curled up and unable to extend, abdominal pain as if breaking, visual disturbances such as seeing flowers/sparks, or alternating chills and fever, traction of the bilateral tendons in the neck preventing flexion and extension, stiff neck and strong back, red and yellow eyes, desire to turn the eyes but only able to close them and look sideways. This disease, named "Qing Jin Qian," originates in the three months of spring. The source moves from the Foot-Jueyin Liver Meridian to the Foot-Shaoyang Gallbladder Meridian. At this time, Shaoyang Qi begins to emerge, and Shaoyin Qi begins to decline. Yin and Yang become stagnant in the Cou Li (interstices of skin and muscles), causing the Zang-Fu organs to receive harsh pathogens and become diseased. If the Fu organs are deficient, they are injured by Yin pathogens, resulting in fever; if the Zang organs are excessive, they are damaged by Yang toxins, resulting in aversion to cold.