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[General Principle] Zhang Zhongjing stated: If a patient presents with high body heat but desires to be covered with clothing, it indicates that the heat is in the skin (superficial exterior) and the cold is in the bone marrow (deep interior). If a patient presents with severe body coldness but does not desire to be covered with clothing, it indicates that the cold is in the skin and the heat is in the bone marrow.

[Commentary] Zhao Sizhen stated: In detail, examining Zhang Zhongjing's discussions, he only distinguishes between the skin and the bone marrow, rather than using the terms "exterior" (Biao) and "interior" (Li). This is because, according to the *Suwen* (Basic Questions), the five tissues—skin, flesh, vessels, sinews, and bones—are the external correspondences of the Five Zang Organs, governing the exterior and filling the body. Only when referring to the Zang and Fu organs can one speak of exterior and interior relationships. Thus, the skin is located above the bone marrow, representing the superficial external layer; the bone marrow is located beneath the skin, representing the deep external layer. This differs from the principle where meridians and zang-fu organs belong to the interior. Moreover, since Zhang Zhongjing placed this syndrome at the beginning of the *Taiyang Chapter*, it is clearly an exterior syndrome. Therefore, we understand that individuals who are constitutionally weak and prone to cold, upon contracting pathogenic factors and developing fever, have heat pathogens that are superficial and cannot overcome the deep-seated cold. Consequently, they feel fearful of the cold externally and desire to be covered. This is what is meant by "heat in the skin, cold in the bone marrow," and the treatment should employ acrid-warm herbs. Conversely, for individuals who are constitutionally robust and prone to heat, or for wine drinkers in the early stage of re-contracting pathogenic factors, if the cold has not yet transformed into heat, yin pathogens close off the latent heat from the outside, with yin condensing externally and heat郁 (stagnating) internally. Thus, they feel internal irritability and do not desire to be covered. This is what is meant by "cold in the skin, heat in the bone marrow," and the treatment should employ acrid-cool herbs. It is essential that after inducing sweating once, both the exterior pathogen is dispersed and the healthy qi is harmonized; this is the profound meaning implicit in Zhang Zhongjing's work. If one were to consider the skin as the exterior and the flesh/bones as the interior, then in the *Mahuang Tang* (Ephedra Decoction) syndrome characterized by joint pain, could it be named as having both exterior and interior involvement?

Wei Yilin stated: Regarding the clause "heat in the skin," Zhang Zhongjing did not prescribe a formula. It is appropriate to first administer Yangdan Tang (Yang Guarding Decoction). Once the cold is resolved, subsequently administer Xiaochaihu Tang (Minor Bupleurum Decoction) with added Guizhi (Cinnamon Twig) to warm the exterior.

Shen Jin'ao's Note: Since commentators interpreted the skin and bone marrow in this clause through the lens of exterior and interior, later generations followed this error. Zhang Zhongjing's treatise mentions many cases of exterior-heat/interior-cold and exterior-cold/interior-heat. Why would this specific clause avoid the terms exterior and interior, preferring instead to specify skin and bone marrow? This makes the logic clear. Therefore, only Zhao's explanation is precise and insightful, surpassing others in understanding, sufficient to dispel millennia of confusion. As for exterior-heat and interior-cold, this constitutes a Shaoyin Syndrome (Shaoyin Disease), which is detailed in the *Shaoyin Chapter*.