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The *Classic of Difficult Issues* (Huangdi Neijing) states: "If one is injured by cold in winter, one will inevitably suffer from warm disease in spring." It also says: "If one fails to store essence in winter, one will inevitably suffer from warm disease in spring." Although both refer to suffering from warm disease, why must they be distinguished as being caused by "injury by cold" versus "failure to store essence"? What is the rationale? The answer is that these are all cases of latent pathogenic qi (pathogenic factors lying dormant within the body). In severe cases of cold damage (Shanghan), illness occurs immediately during winter; in mild cases, illness does not occur immediately. Instead, the pathogenic qi lies dormant in the muscle-coupling (the space between skin and muscle) and the Shaoyin channel. When yang qi opens and disperses in spring, it stirs up the latent pathogenic qi, causing illness. This is the first scenario. Western medicine posits that the incubation period does not exceed fourteen days, denying the logic of contracting cold in winter and falling ill in spring. This view lacks deep reflection on diseases like smallpox and measles, which stem from congenital toxins and can remain latent for ten to thirty years. The transition from winter to spring is but a fleeting moment; how can one definitively rule out such illnesses? Regarding the concept of "failure to store essence," commentators argue that it does not exclusively refer to yin essence. For instance, if winter should be cold but is not, or if peach and plum trees blossom out of season, these are examples. If the climate is not cold, yang pathogens emerge early, consuming and depleting yin fluids, leading to an internal deficiency of kidney essence. When spring arrives and yang qi expands, new pathogens may trigger latent pathogens, causing illness. Humans share the same qi with heaven and earth. Disharmony in climate, through contact and accumulation over time, eventually gives rise to disease. This is the second scenario. The *Classic* further states: "Diseases occurring before the Summer Solstice are called warm diseases; those occurring after are called summerheat diseases." Summerheat is heat. Before the Summer Solstice, the climate is mild and warm, so those who contract it develop warm disease according to the seasonal change. After the Summer Solstice, the climate is intensely hot, so those who contract it develop summerheat disease according to the seasonal change. Warm disease is milder than heat disease, while heat disease is more severe than warm disease. This is the third scenario. Although warm and heat conditions vary with the seasons, fundamentally, if the condition is more severe than warm disease, it is classified as heat disease. One cannot claim that there are absolutely no heat diseases before the Summer Solstice. Eastern medicine considers humans as homeothermic animals. Measured by a thermometer, normal body temperature typically ranges between 36.5°C and 37.5°C. Winternitz defined subfever as 37.5°C to 38°C; light fever as 38°C to 38.5°C; moderate fever as 38.5°C to 39.5°C; high fever as 39.5°C to 40.5°C; and extreme fever as above 40.5°C. However, once body temperature exceeds 40°C, the patient has no hope of survival. The rules using the Fahrenheit scale starting from 98°F are identical. Subfever and light fever correspond to warm disease categories; high fever and extreme fever correspond to heat disease categories. Observing this, the meanings of "warm" and "heat" become clear as ice melting.