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(Commentary on the manuscript by disciple Wu Yuchun)

Medical generations have produced famous sages, yet their writings often mutually refute and attack each other. Therefore, among various theories, some appear correct but are actually incorrect, while others appear incorrect but are actually correct. Examining the syndrome of "swallowing acid" (Tun Suan), Liu Hejian stated: "Acidity is the flavor of Liver Wood. It arises because excessive Fire controls Lung Metal, preventing it from pacifying Liver Wood; thus, Liver Wood becomes hyperactive and generates acidity." Crops belong to Earth, with a sweet flavor; now Wood counter-attacks Earth, carrying turbid qi upward, rushing to the throat to become acidic. To classify swallowing acid as a Liver disease, Hejian's insight can be considered outstanding for all ages. However, he insisted on interpreting it through "excessive Fire," which stems from his focus on Fire syndromes, making his view somewhat biased. Consequently, Zhang Jingyue deeply disagreed, insisting on Li Dongyuan's theory of "Cold" to debate him.

Jingyue stated: "When a person's Stomach Yang is vigorous and transportation functions normally, how could there be acidity? Only when Fire power is weak, leading to sluggish transportation, will food stagnate and fail to move, becoming acidic and putrid." Jingyuan followed Dongyuan, establishing his theory on Deficiency-Cold. His view was indeed valid and without error. However, he omitted mention of the Liver. This was likely because, in overly refuting Hejian, he discarded Hejian's theory of "Liver Wood self-hyperactivity."

Generally, when food enters the Stomach, clear fluids ascend and turbid fluids descend. Without the accumulation of Dampness and Cold, swallowing acid cannot occur. Yet, even if Dampness and Cold accumulate, if Liver Wood does not stagnate within Earth (Spleen/Stomach), there would merely be an overflow of saliva and clear water, insufficient to cause swallowing acid. The reason is that the Spleen and Stomach detest Dampness. Patients with swallowing acid must first have Damp-Turbidity stagnant in the Stomach, suppressing the ascending nature of Liver Wood so it cannot reach the upper body. When clear fluids do not ascend, turbid fluids reverse upwards. The contents of the Stomach, instead of being transformed into essence by the steaming and changing action of Mingmen Fire, all undergo fermentation due to Liver Wood stagnation, producing an acidic taste.

Thus, Hejian's theory of "Liver Wood self-hyperactivity" is indeed sufficient to serve as a model for future generations. Meanwhile, Jingyue's words regarding "Spleen Yang deficiency-cold, stagnation accumulation, and Qi oppression" are especially sufficient to supplement Hejian's omissions and elucidate the profound meaning of Dongyuan's theories. Furthermore, since the nature of Liver prefers coolness, Hejian's treatment using cold purgatives is appropriately applied. If Earth is prosperous, Metal is generated; if Metal is generated, it controls Wood, preventing Wood from attacking Earth. In such cases, Jingyue's treatment of warming the Spleen and promoting Stomach function is logically appropriate.

Reading Xue Lizhai's statements reveals that what *Neijing* refers to as "Fire" describes the manifestation of the disease, while what Dongyuan refers to as "Stomach Cold" describes the root of the disease. Synthesizing the theories of these two masters and understanding them together, we know that ancient discussions each contain exquisite intent. One should neither rashly accuse ancients of being wrong nor flatteringly accept them as entirely right without deeply seeking the reasons for their correctness.