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When the tongue coating is black in the center extending to the tip, it indicates that heat pathogen has penetrated deeply. If seen in *Lianggan* (simultaneous infection of exterior and interior meridians), nine out of ten cases are fatal. If accompanied by severe aversion to cold, it is also a death sign. If there is no aversion to cold but with diarrhea, it is treatable; *Tiaowei Chengqi Tang* (Stomach-Regulating Purging Decoction) should be used as the main treatment.

[Commentary by Jie] *Lianggan* refers to the condition where both Yin and Yang meridians are injured, and exterior and interior diseases occur simultaneously. For example, when *Taiyang* (Greater Yang) and *Shaoyin* (Lesser Yin) meridians are diseased together, symptoms include headache, dry mouth, and vexation with fullness. When *Yangming* (Bright Yang) and *Taiyin* (Greater Yin) meridians are diseased together, symptoms include body heat, delirious speech, abdominal fullness, and loss of appetite. When *Shaoyang* (Lesser Yang) and *Jueyin* (Terminal Yin) meridians are diseased together, symptoms include deafness, retraction of the scrotum, and cold limbs. If all three Yin and three Yang meridians are affected, food and fluids cannot be taken, and the patient becomes comatose and unaware; death typically occurs on the sixth day. This corresponds to the statement in the *Neijing* (Inner Canon): "Those who suffer from simultaneous cold infection will inevitably die." In this context, due to the cold pathogen stagnating for a long time and transforming into heat, moving from the Three Yang meridians into the *Jueyin* meridian, the tongue shows yellow coating on the edges and black in the center extending to the tip. At this stage, heat scorches the liver fluids, internal wind has stirred, and the nine orifices are about to close. This inherently belongs to a critical deterioration (*Huai Zheng*), hence saying nine out of ten die. Regarding those who die due to severe aversion to cold, this aligns with Zhang Zhongjing's statement: "In all cases of *Jue* (cold extremities), it is because Yin and Yang qi do not connect smoothly. *Jue* manifests as cold hands and feet." It also corresponds to the sign: "In cold damage after six or seven days, if the pulse is faint, hands and feet are cold, and there is vexation, after moxibustion on the *Jueyin* meridian, if the cold extremities do not return, death ensues." The case of no aversion to cold but with diarrhea involves heat from *Yangming* merging with *Jueyin*, gradually depleting kidney fluids, causing dry fecal matter in the intestines to force fluid downward, resulting in spontaneous purging of clear water. Therefore, *Tiaowei Chengqi Tang* is used to clear stomach heat and purge dry feces. This mirrors Zhang Zhongjing's description: "In *Shaoyin* disease, spontaneous purging of clear water, pure green color, pain in the epigastrium, and dry mouth indicate the need for urgent purging with *Dachengqi Tang*." (*Tiaowei Chengqi Tang* formula is cited previously).

When the tongue coating is pale red on the outside and pale black in the center, if accompanied by aversion to wind, it indicates that the exterior syndrome has not yet resolved. Use half doses of *Shuangjie San* (Double Release Powder) and *Jiedu Tang* (Detoxification Decoction) combined to induce slight sweating. After sweating resolves the exterior, proceed with purging. If *Jietong* (chest binding/collapse) occurs with vexation and fixed staring gaze, it is untreatable. If it is not *Jietong*, it is treatable.

[Commentary by Jie] When cold damage pathogens enter the interior and transform into heat, moving from *Yangming* into the Three Yin meridians, the tongue appears red on the edges and pale black in the center. If external signs show aversion to wind, it is known that the exterior has not resolved. Although termed aversion to wind, it actually encompasses aversion to cold, as aversion to wind invariably accompanies aversion to cold, and vice versa. One should use *Shuangjie San* combined with *Jiedu Tang* to clear heat internally and release the exterior externally. After sweating resolves the exterior, examine the tongue coating; if dry, with hardness and fullness around the navel and abdomen, and constipation, then use *Chengqi Tang* to purge. However, if purgatives are mistakenly used while the exterior pathogen remains, leading to heat sinking inward due to incorrect purging, *Jietong* may form. Alternatively, injury to heart and kidney fluids may cause yin exhaustion and yang floating, resulting in vexation; or injury to liver fluids may cause fixed staring gaze; these are untreatable conditions. If mistaken purging leads to abdominal fullness and intermittent pain without forming *Jietong*, and without dangerous signs like vexation or fixed staring gaze, rescue measures can still be attempted. Only when the center of the tongue is black and withered, lacking accumulated coating, with edges not crimson, or having only slight prickles, does it indicate dehydration and blood dryness. In such cases, nourishing fluids and generating Jin-Ye (body fluids) urgently is required, and purgative agents must not be used recklessly. (*Shuangjie San* and *Jiedu Tang* formulas are cited previously).