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Zhou Yu-zai said: If one is injured by cold in winter, one will surely suffer from heat disease in summer. This implies that "heat disease" stands in opposition to "spring-warmth," and is not the heat contracted during the summer season itself.

However, Jia-yan (Yu Chang), while discussing the six qi of heaven, pointed out that spring, autumn, and winter each govern one qi, whereas summer exclusively governs three qis (summer-heat, dampness, and fire/heat). What he referred to as "spasm" and "dampness" are still conditions caused by immediate external pathogenic factors, rather than latent cold hidden within the body that manifests as heat only in summer. Therefore, this statement refers to individuals who already have latent qi about to erupt and subsequently contract dampness. If one merely suffers from spasm or dampness, it cannot be immediately classified as heat disease. Thus, heat disease originates from within the body. Regardless of which meridian symptoms may accompany it, it must necessarily pass through the Yangming Meridian, and there are no exterior signs. If exterior signs are present, they must result from external contraction of wind pathogens. One should not hastily administer Baihu Tang (White Tiger Decoction); instead, the external pathogens must first be resolved before the primary formula can be used. This also follows the method of treating the exterior first and the interior later.

He further stated: Heat disease is essentially latent cold. Those who contract cold in winter and manifest it in spring are diagnosed with warm disease; those who manifest it in summer are diagnosed with heat disease. Why does some manifest in spring and others in summer? This is because the severity of the pathogenic contraction differs, human constitutions vary in strength, and triggering factors are distinct. Some cases arise from irregular diet or excessive physical labor, while others result from sexual indiscretion and exhaustion. In spring, although the wind-wood qi prevails, if the vital qi and blood do not significantly decline, the contact with pathogens occurs at different times, preventing immediate manifestation. By summer, yang qi is fully dispersed, and the fire command dominates, coinciding with the flourishing of damp-earth qi. At such a time, how could the pathogen remain latent? Consequently, the origin of heat disease lies in the Shaoyin Kidney Meridian, and its pathway of emergence is the Yangming Stomach Meridian. For warm disease, the pathway of emergence is the Shaoyang Gallbladder/Liver Meridian. Although the involved meridians differ, they generally do not depart from the Yangming and Shaoyang meridians, owing to the influence of seasonal qi. However, since the onset is delayed, the heat becomes more intense. This explains why Zhang Zhongjing employed Shigao (Gypsum Fibrosum) to clear stomach heat, Zhimu (Anemarrhenae Rhizoma) to purge latent kidney pathogens, and Gancao (Licorice Root) and Jingmi (Oryza Sativa) to support middle jiao qi. The decoction is named "Baihu" (White Tiger). White corresponds to metal and coolness; wind arises from the tiger and is fierce. When people encounter stifling heat and irritability, feeling helpless, suddenly a fierce wind arrives, bending grass and stirring waves. The fiery wheels and fire trees instantly transform into a cool world, bringing relief and satisfaction.