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The nature of fire varies, yet all can be used for cooking or burning. In contemporary times, the selection of wood for fuel is generally based on the principle that "Wood generates Fire," corresponding to the fires of the five seasons. In reality, the nourishing benefits of fire are closely related to the onset of diseases and longevity; this is not without reason. However, people today do not study this matter because they only view the fire from stoves and hearths as a method derived from burning firewood. Who would know that the fire obtained by drilling wood (drilling-fire) offers profound benefits to humans? I now elucidate its principles, hoping that gentlemen will adopt them.

In spring, it is appropriate to use firewood from elm and willow trees. The qi of these trees receives the spring qi earliest, and their leaves turn green before other trees. Using their fire to generate spring qi ensures that one will suffer no stagnation-related illnesses throughout the season. In summer, it is appropriate to use firewood from jujube and apricot trees. Their qi fully embodies the summer heat, and consequently, their hearts are purely red. Using their fire to promote summer qi prevents vomiting and diarrhea during the season. In autumn, it is appropriate to use firewood from oak trees. The qi of oak trees largely reflects the autumnal energy, and thus its grain is white. Using its fire to gather autumn qi prevents malaria and dysentery in autumn. In winter, it is appropriate to use wood from locust and sandalwood trees. These woods are very hard due to receiving the winter cold. Using their fire to store winter qi prevents illnesses caused by severe cold throughout the winter.

During the late summer (the transitional period between summer and autumn), it is appropriate to use wood from mulberry and zhe trees. These woods possess the harmonious qi of late summer, and their texture appears yellow. Using their fire to harmonize the qi of the four seasons prevents damp-heat illnesses during this period. People in ancient times did not suffer from various diseases; although their temperaments were tranquil and quiet, this was also attributable to the benefits of fire. The stove fire used by people today is merely the fire passed down from burning firewood; it inevitably contains impurities and cannot effectively dispel disease. Furthermore, fire struck from stones causes greater harm and is inferior to the fire from burning wood. Those who seek longevity and immortals who specifically revere water and fire should certainly pay attention to this.