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In the disease of Shanghan (Cold Damage), nothing is more primary than distinguishing the meridians and the levels of exterior and interior. In treating exterior and interior conditions, nothing is more urgent than distinguishing the urgency of sweating (diaphoresis) and purging methods. If there is even a slight error in the timing of sweating or purging, hundreds of complications will arise. Therefore, predecessors discussing the treatment of Shanghan stated that "sweating medicines should be used early, and purging medicines should be used late." These two phrases constitute a crucial principle.

"Sweating should be early" means that when wind-cold pathogens enter from the exterior, one should promptly use exterior-releasing methods to resolve the pathogen from the surface, preventing it from transmitting inward and causing internal disease. This aligns with Zhang Zhongjing's saying: "Once a disease is detected, it must be treated immediately, regardless of morning or night."

"Purging should be late" means that when wind-cold pathogens have transmitted into the interior, purging methods must only be employed when the "Zheng Yang Yang Ming" (Positive Yang Bright Yang) fu-organ syndrome is established. One must wait until the pathogenic heat is abundant and congested within the interior; only then can purging remove the pathogenic heat and achieve recovery. This is referred to as "acting when action is required, which appears as not acting rashly." If purging is applied prematurely before the pathogenic heat has become abundant in the interior, it will damage the healthy qi. The cold qi from paralogous diarrhea will take advantage of the deficiency to cause stagnation and accumulation. This corresponds to Zhang Zhongjing's warning that premature purging may lead to Pi Qi (stagnation syndrome) or Jie Xiong (chest binding syndrome).

The mention of "early and late" here refers to the sequence of therapeutic strategies, not the specific time of day. However, some individuals mistakenly believe that sweating should occur during the morning (yang phase) and purging during the afternoon (yin phase), interpreting "early and late" solely based on the time of day. Such interpretations are fragmented and far-fetched, none being more egregious than this.

Furthermore, those who neither understand the treatment principles of Shanghan nor recognize miscellaneous diseases that mimic Shanghan often administer sweating or purging drugs recklessly. This damages the yuan qi (original qi) of constitutionally weak patients, leading to a proliferation of complications, invariably resulting in death.

The *Classic* states: "For fullness in the chest and abdomen, drain from within"; and again, "When earth qi is stagnant, use the method of seizure (purging)." This implies using purging to promote drainage and dispersion. However, to attack the branch manifestations of pathogenic factors, one must first examine the root of healthy qi. For instance, in Shanghan, if the cun pulse at the wrist is weak and powerless, emetic therapy is strictly contraindicated; if the chi pulse is weak and powerless, sweating and purging are strictly contraindicated. In such cases, Xiao Chai Hu Tang (Minor Bupleurum Decoction) should be used to harmonize.

If urination is frequent and red, stool is constipated, and the pulse is deep and solid, although the number of days since onset is small, the pathogen has already transmitted to the interior, and purging is indicated. Failure to purge will result in the accumulation of heat that cannot dissipate, leading to symptoms such as jaundice and mania.

If the pulse is floating and large, and urination is clear and profuse, although many days have passed, the pathogen has not transmitted to the interior, and heat consolidation has not formed. Purging is contraindicated. Applying purging would deplete yin fluids. With yin qi weakened in the middle, yang pathogenic factors will attack internally, a situation described as "inviting thieves to break up the household."

Additionally, conditions involving unripe food retention, incomplete resolution of exterior pathogens, blood loss, ulcers, moving qi, nausea, powerless pulses across all positions, peaceful sleep, constipation due to deficiency in the elderly, prolonged illness, and postpartum states are all contraindications for harsh purging. In cases of internal injury with insufficient yuan qi accompanied by food stagnation, tonification and purging should be combined. Use Bu Zhong Yi Qi Tang (Tonify the Middle and Augment the Qi Decoction) with cooked Da Huang (Rhei Radix et Rhizoma) added to moisten and promote movement.

Moreover, concurrent Taiyang and Shaoyang diseases represent half-exterior, half-interior syndromes, which require harmonization. Misapplication of purging will cause Taiyang exterior pathogens to sink into the interior, forming Jie Xiong (chest binding); Shaoyang interior pathogens will attack the intestines and stomach, forming Zang Jie (z visceral binding), or cause intestinal洞泄 (profuse watery diarrhea) and incontinence of urine and feces, leading to death.

Therefore, fever with aversion to cold indicates the pathogen is in the exterior; sweating is permissible, purging is not. Fever with aversion to heat indicates heat is in the interior; purging is permissible, sweating is not. When the pathogen is in the half-exterior, half-interior region, both sweating and purging are prohibited. People often say that excessive sweating leads to the loss of yang, but they do not realize that excessive purging also leads to the loss of yang. This is because purging excessively depletes the yang within yin, hence it is termed the loss of yin.

If there is no vomiting, no thirst, peaceful sleep, no high fever, but only pain in the epigastrium, occasional desire to eat, frequent dysentery, and a white tongue coating, this indicates cold in the chest and heat aggregated in the lower dantian. This is called Zang Jie (visceral binding). Because pathogenic factors are bound in the middle, qi cannot circulate downward, causing epigastric pain. If the white coating persists, it indicates excess cold in the upper jiao. Excess cold makes the binding more solid. In Shanghan, abundance of yang is a favorable sign, while abundance of yin is an unfavorable prognosis.

If, on the fifth or sixth day, there is no congestion in the chest, but restlessness and insomnia during the day, with slight calmness at night, this results from excessive purging and sweating leading to the depletion of yin and yang. Daytime governs yang; during the day, yang qi attempts to recover, but due to deficiency, it cannot resist the pathogen, causing restlessness. Slight calmness at night occurs because deficient yang cannot contend with the pathogen, and the pathogenic heat encounters yin, providing slight relief.

If yin and yang have not yet collapsed, yin recovers at night and yang recovers during the day. After several days, yin and yang gradually recover, and the pathogenic qi will naturally retreat. If symptoms worsen daily, this indicates that healthy qi is scattered internally and pathogenic qi is rampant in the middle; this is incurable.

However, after sweating or purging in Shanghan, one must not immediately use strong tonics like Ren Shen (Ginseng Root). Instead, Xiao Chai Hu Tang (Minor Bupleurum Decoction) modified should be used to harmonize. If strong tonics are added immediately, the pathogenic qi receives nourishment, and heat becomes more vigorous. This is why it is said that "there is no tonification method in Shanghan." Only in cases of Shanghan-like diseases complicated by deficiency with powerless pulses, or Shanghan caused by overexertion, is tonification not prohibited. Furthermore, one must distinguish between yin and yang syndromes.

Yin syndromes manifest as: stillness and heaviness of the body, silent speech, difficulty in breathing, cold breath from mouth and nose, cool body, inability to swallow liquids, incontinence of urine and feces, and aversion to cold on the face.

Yang syndromes manifest as: restlessness and lightness of the body, audible speech, hot breath from mouth and nose, and a burning-hot body.

Differentiation must further rely on whether the pulse is powerful or powerless.