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In cases of Yang Jue (Yang collapse with cold extremities), the hands and feet are cold; in some cases, the cold extends beyond the elbows and knees, or even the fingernails and toenails turn cyanotic and black. In severe cases, the entire body becomes ice-cold like stone, blood coagulates into patches of cyanosis, or the six pulses are powerless, or the pulse is faint and nearly imperceptible. The above pulse and symptom manifestations all appear as pure Yin syndrome, yet why is it still considered a Yang syndrome? Upon careful examination of internal symptoms, breath sprays out like fire, gums rot and there is foul odor, restlessness, thirst, and delirious speech, dry mouth and tongue, yellow or black tongue coating or prickles on the tongue, epigastric and abdominal fullness and obstruction, lower abdominal pain, dark red urine that passes drop by drop with pain. This is either dry fecal impaction or sticky closure of the large intestine, or diarrhea with heat binding, or heat accumulation with purgation of clear fluid. All three internal jiaos manifest Yang syndrome characteristics, hence it is called Yang Jue. Unskilled physicians fail to investigate thoroughly; although there are internal excess syndromes requiring purgation, they only see the external cold signs and purely Yin pulse qualities, mistakenly administering warming agents, bringing disaster swiftly.

Cases where Yang syndrome resembles Yin occur in both warm epidemics and true cold damage; however, cases where Yin syndrome resembles Yang belong exclusively to the domain of true cold damage and do not occur in warm epidemics, thus they are not included here (see *Shanghan Shilu* for details).

In warm epidemics, when Yang syndrome resembles Yin, it begins at the Mo Yuan (membrane source) and gradually transmits inward. It first presents with fever for several days, followed by cold extremities (Si Ni). In true cold damage, when Yang syndrome resembles Yin, it initially presents with fever from the Yang meridians, with a floating and rapid pulse. Pathogenic factors transmit inward gradually from the exterior; internal Qi becomes congested and blocked, causing the pulse to become deep, leading to cold extremities, which takes more than one day to develop. In true Yin syndrome, it begins with aversion to cold without fever, with a deep and fine pulse, immediately requiring Si Ni Tang (Four Reversals Decoction); if Aconite is urgently administered to restore Yang, and treatment is delayed for two or three days, death ensues.

A concise method for differentiation: In Yang syndrome resembling Yin, the exterior is cold but the interior is necessarily hot, so urine is dark red. In Yin syndrome resembling Yang, this is Ge Yang syndrome (floating Yang), characterized by upper heat and lower cold, so urine is clear and white. Relying solely on whether urine is red or white ensures absolute accuracy in diagnosis.

I once encountered a mild epidemic case where a physician mistakenly administered Bai Hu Tang (White Tiger Decoction) for several doses, subsequently developing cold extremities and worsening pulse condition. Another physician erroneously diagnosed it as a Yin syndrome and prescribed Fu Zi Tang (Aconite Decoction), resulting in recovery. This was not treating the disease but treating the iatrogenic effects of medication; although the pathogen was misidentified, the remedy happened to be correct by chance. The physician's incompetence became the patient's fortune. The illness was originally self-limiting and would have resolved without medication. However, continuous administration of the harsh, cold-natured Bai Hu Tang suppressed Stomach Qi, causing cold extremities and forcing the epidemic pathogen to lie dormant, thereby aggravating the condition. The subsequent use of warming agents allowed Stomach Qi to circulate freely, dispersing the residual pathogens, leading to recovery. If it were a direct attack on the Yin channels without any Yang presence, a single dose of Bai Hu Tang would cause immediate death; how could multiple doses be tolerated?