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Wang Haizang stated: In treating cold damage (Shanghan), one must distinguish between exterior and interior syndromes. If the exterior and interior are not distinguished, errors in sweating (diaphoresis) or purging will occur; is this not a major mistake? For example, both present with fever. If there is body heat but no thirst, this indicates heat in the exterior; it should be treated with Xiao Chai Hu Tang (Minor Bupleurum Decoction) plus Guizhi (Cinnamon Twig). If there is limb coldness (Jue) with a slippery pulse, this indicates heat in the interior; it should be treated with Bai Hu Jia Ren Shen Tang (White Tiger Decoction plus Ginseng). Both present with water-fluid retention causing dry heaving, slight diarrhea, fever, and cough; this indicates water in the exterior; it should be treated with Xiao Qing Long Tang (Minor Blue Dragon Decoction) plus Yuan Hua (Genkwa Flower). If the body is cool, the exterior syndrome has ceased, and there is coughing with pain under the ribs, this indicates water in the interior; it should be treated with Shi Zao Tang (Ten Jujube Decoction). Both present with aversion to cold accompanied by fever. If aversion to cold is prominent, the disease originates from the Yang aspect; it should be treated with Ma Huang Tang (Ephedra Decoction), Gui Zhi Tang (Cinnamon Twig Decoction), or Xiao Chai Hu Tang. If there is no fever but only aversion to cold, the disease originates from the Yin aspect; it should be treated with Fu Zi (Aconite Root) or Si Ni Tang (Frigid Extremities Decoction). Both present with body pain, floating pulse, fever, and headache. If body pain is present, the exterior is unresolved; it should be treated with Ma Huang Tang. If the pulse is deep, there is spontaneous diarrhea, and body pain, the interior qi is discordant; it should be treated with Si Ni Tang. From these observations, Zhang Zhongjing's methods for distinguishing exterior and interior are very detailed. Students should investigate them deeply and attentively.

The *Huoren Shu* (Book of Vitality) states: Fever, aversion to cold, body pain, and a floating pulse constitute an exterior syndrome. The characteristic of an exterior syndrome is aversion to cold. Aversion to cold belongs to the Taiyang (Greater Yang) channel and is suitable for diaphoresis. If there is no aversion to cold but rather aversion to heat, with sweating on the palms and axillae, dryness in the stomach, accumulated feces, tidal fever, hard stool, normal urination, abdominal fullness, wheezing, or delirium, and a deep and slippery pulse, this constitutes an interior syndrome. The characteristic of an interior syndrome is internal heat. Internal heat belongs to the Yangming (Yang Brightness) channel and is suitable for purging. Cold damage initially presents with fever and aversion to cold. Now, after sweating, there is no aversion to cold, but doubled fever and restlessness. Initially the pulse was floating and large, now it is surging and solid, or deep, rapid, thin, or fine. Initially the spirit was calm, now there is狂语 (delirious speech). This indicates excess in the stomach and hyperactive Yang; another sweat will cause death. Purging is required for recovery. There are also cases where the disease immediately transforms into a Yang-excess syndrome upon onset, requiring immediate purging without being bound by the number of days. Furthermore, if there is severe distension and stuffiness from the chest to the umbilicus and abdomen, abdominal pain, inability to sit or lie comfortably, dizziness, stuffiness, and urgent wheezing, extreme cases may require purging regardless of other symptoms. If purging is not performed, Qi and Blood will not flow, leading to cold extremities. Physicians who do not understand this may mistakenly suspect Yin-cold collapse and administer hot medicines, causing disaster instantly. This must be carefully examined.

Cheng Wuji said: Pathogenic factors lodging in the exterior are called cold pathogens. When they contend with Yang, they manifest as cold. Pathogenic factors entering the interior are called heat pathogens. When they contend with Yin, they manifest as heat. Pathogenic factors in the half-exterior half-interior contend outwardly with Yang to manifest as cold, and inwardly with Yin to manifest as heat. Therefore, in alternating chills and fever, if pathogenic factors are more in the exterior, chills predominate; if more in the interior, heat predominates; if half in the exterior and half in the interior, chills and heat are equal. Pathogens in the exterior must be resolved by steeping the form to induce sweating. Pathogens in the interior must be cleared by scouring to promote bowel movement. Those neither strictly exterior nor interior, but in the half-exterior half-interior, are not suitable for sweating, vomiting, or purging; harmonization is appropriate. Xiao Chai Hu Tang is a harmonizing formula.

Li Dongyuan said: Pathogens between Ying (Nutritive) and Wei (Defensive) levels are called half-exterior half-interior. Between the Taiyang and Yangming channels, the Shaoyang (Lesser Yang) channel resides in the half-exterior half-interior of the body. Wu Ling San (Five-Ingredient Powder with Poria) regulates the half-exterior half-interior of the Bladder channel. Li Zhong Tang (Regulate the Middle Decoction) treats the half-exterior half-interior above and below in cases of vomiting and diarrhea.

The *Huoren Shu* further states: Exterior syndromes in cold damage should be treated with diaphoresis, and interior syndromes with purging; this is an unchangeable principle. Releasing the exterior and attacking the interior are fundamentally different; Gan Sui Shen Dan cannot be drunk together, and how can Gui Zhi Tang and Cheng Qi Tang be administered simultaneously? However, suppose a patient has a floating and large pulse, indicating an exterior syndrome suitable for sweating, yet suffers from fever, irritability, thirst, and red urine, requiring purging. This indicates simultaneous exterior and interior manifestations; Wu Ling San should be used. Suppose cold damage involves constipation for six or seven days, with headache and fever, indicating an interior syndrome suitable for purging. If the urine is clear, it is known that the disease is not in the interior but remains in the exterior, and sweating should be induced. This indicates both syndromes are present, so purging should not be attempted yet; Gui Zhi Tang should be given. Suppose a patient has epigastric fullness, lack of desire to eat, hard stool, and a deep-thin pulse, indicating an interior syndrome suitable for purging. However, if there is sweating only on the head, slight aversion to cold, and cold hands and feet, sweating should be induced. These simultaneous syndromes correspond to Zhang Zhongjing's description of "half in the exterior, half in the interior," treated with Xiao Chai Hu Tang. Suppose Taiyang disease exterior syndrome persists, but the physician repeatedly purges, leading to persistent diarrhea with heat, and epigastric hardness. Zhang Zhongjing calls this unresolved exterior and interior, treated with Gui Zhi Ren Shen Tang (Cinnamon Twig and Ginseng Decoction). Originally Taiyang disease, but the physician incorrectly purged, resulting in abdominal pain; this indicates both exterior and interior involvement. Zhang Zhongjing uses Gui Zhi Jia Shao Yao Tang (Cinnamon Twig Decoction plus Peony Root); for severe pain, Gui Zhi Jia Da Huang Tang (Cinnamon Twig Decoction plus Rhubarb). It is also stated: In Taiyang disease with Gui Zhi syndrome, if the physician incorrectly purges, causing persistent diarrhea, a rapid pulse indicates the exterior is unresolved; wheezing with sweating is treated with Ge Gen Qin Lian Tang (Kudzu, Scutellaria, and Coptis Decoction). Irritability, bitter taste, abdominal fullness, wheezing, fever, sweating, no aversion to cold but aversion to heat, constitutes a Yangming syndrome. Yet the pulse is floating and tight, indicating simultaneous exterior and interior; neither sweating nor purging is suitable; Zhi Zi Tang (Gardenia Decoction) should be used to induce vomiting.

This is Zhang Zhongjing's method for treating cold damage with both exterior and interior syndromes. Wang Haizang said: Da Chai Hu Tang (Major Bupleurum Decoction) treats syndromes with heat in both the exterior and interior. For treating exterior involvement, if any one or two of the following four signs remain—floating pulse, headache, aversion to wind, or aversion to cold—it indicates the disease has passed its transmission cycle and remains unresolved. For treating interior involvement, such as delirium,妄语 (incoherent speech), or throwing hands and staring wildly, these are urgent interior conditions. If one wishes to sweat, the interior condition is already urgent; if one wishes to purge, the exterior condition remains. Generally, Da Chai Hu Tang is appropriate.

After four or five days of cold damage, or even after passing the transmission cycle, if there is no exterior syndrome and the interior syndrome is uncertain, Xiao Chai Hu Tang can be used with modifications according to symptoms, even up to ten or more days. If Xiao Chai Hu Tang fails after ten days, and the stool is hard, allowing for purging based on symptoms, Da Chai Hu Tang should be used for purging. Since the transmission cycle has passed and the patient is slightly deficient, purging is indicated; using Da Chai Hu Tang is stable, as Cheng Qi Tangs may be too harsh for the patient to tolerate. Zhang Zhongjing stated: On the sixth or seventh day, if the eyes are unclear and the pupils do not move freely, with no exterior or interior syndromes, difficulty in defecation, and slight body heat, this is an excess condition requiring purging; Da Cheng Qi Tang (Major Order the Qi Decoction) is appropriate. He also stated: If a patient has no exterior or interior syndromes, with fever for seven or eight days and a floating-rapid pulse, Da Chai Hu Tang can be used for purging. Suppose purging has been performed, but the rapid pulse persists, and after six or seven days there is no bowel movement, this indicates blood stasis; Di Dang Tang (Resist Swarm Decoction) is indicated.