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The *Neijing* (Inner Canon) states: "Jun Fire (Ministerial Fire/Heart Fire) manifests through clarity, while Xiang Fire (Ministerial Fire/Kidney Fire) functions through its position." This distinguishes Yin and Yang based on the virtue of fire, thereby comprehending the principles of form and Qi. Generally, fire belongs to Yang; however, the Yang located above is Yang within Yang, thus it is called Jun Fire (Heart Fire). The Yang located below is Yang within Yin, thus it is called Xiang Fire (Kidney Fire). This is the way of Heaven and Earth's generation. In humans, the upper part is Jun Fire, therefore it is governed by the Heart. The lower part is Xiang Fire, therefore it originates from the Kidney. That which is governed by the Heart serves as the master of Shen (Spirit/Mind), hence it is said that "Jun Fire manifests through clarity." That which originates from the Kidney serves as the root of generation, hence it is said that "Xiang Fire functions through its position."

Regarding their pathology, because Jun Fire transforms into the formless (Xu), its Qi may be obscure or clear. Because Xiang Fire transforms into the formed (Shi), its pathology can burn and blaze. Why? Because that which transforms into the formless is without physical shape; thus, its decline or flourishing is only seen in the Shen (Spirit). The Shen values sufficiency; when deficient, it is fearful. That which transforms into the formed has physical substance; thus, whether it presents as heat or cold, it must adhere to Blood and Qi, providing concrete evidence before it can be termed "Fire." Thus, the distinction between Clear and Turbid requires differentiation as described. However, although Clear and Turbid are two aspects, the endowment of Qi is one. Therefore, if Jun Fire declines, Xiang Fire also fails; this is the deficiency of the formless affecting the formed. If Xiang Fire blazes, Jun Fire also flares; this is the pathology of the formed affecting the formless. Life depends on the completeness of Shen, while disease manifests only in the Form. Therefore, the pathogenic action of Fire must rely on the positioned and formed Xiang Fire. What is called "Pathogenic Fire" is what is called "Ordinary Fire," or "Fire that spreads like a prairie fire." It becomes pathological only when it deviates from correctness. Hence, it is separately named Pathogenic Fire, but in reality, it cannot be discussed alongside Jun and Xiang Fires. Thus, in the *Neijing*, it is also called "Feared Fire." Precisely because this Fire is formed, it is feared.

Since diseases arise from formed Fire, they must be treated with formed substances. Therefore, if Fire is excessive in the Form, it can be purged with Bitter-Cold substances; if Fire is deficient in the Form, it can be assisted with Sweet-Warm substances. This is treating Form with Form, and the method of treating Fire ends here. As for Formless Fire, it generates life continuously, profound and mysterious. It is the transformation of Pre-Heaven, the Shen of Post-Heaven, the mother of life and death, and the gate of the Mysterious Female (Xuan Pin). How could it possibly be simulated within traces of form? Therefore, formed Fire must not be indulged, and formless Fire must not be destroyed. One who can discern the righteousness or pathogenicity of Fire and grasp the power of its fullness, emptiness, expansion, and contraction, will preserve the Shen, dispel disease, and hold the Dao of life in their hands. Even with a physical body, what is there to worry about?