或曰如子之言。伤寒因于寒。瘴疟因于热。则北地多寒。伤寒乃北方之病。南地多热。瘴疟
乃南方之病欤。予曰子言亦有理。上古圣人。亦有异法方宜之
论。然不可执一不通。第曰北方伤寒病多。南方瘴疟病多。则可。若曰北方无瘴疟。南方无伤寒。
则不可。盖天道无常。假令北方暑热过多。秋时暴热数日。北人感此气。亦多病瘴。广之东南。
设有冬时大寒数日。南方素无寒。若感此气。亦多病伤寒。故医者当上察天时四时温凉寒热。
上明五运六气司天在泉之理。下察四方风土之宜。中辨病患平日之性。宜凉宜热。平日是何脉。再
审今病。或外伤风寒暑湿。或内伤饮食劳役七情男女。或感乖戾之气而为瘴灼。见其病之在何经
何脏。宜补宜泻宜吐宜汗宜温宜和解。万举万全。庶不愧为医矣。
夫人身自胸膈至头为上焦。其气象天。自胸膈至腹为中焦。其气象人。自腹至足为下焦。其
气象地。以五行论之。上焦属丙丁火。中焦属戊己土。下焦属
壬癸水。在五脏。心肺阳也居上。脾阴坤土也居中。肾肝阴也居下必也。阴能升。阳能降。以成
水火之既济。天地之交泰。则为平人。若夫发瘴之地。秋冬多热。则人身阴阳之气。上者自上。下者自下。
而成水火之未济。天地不交之否。故一触外邪。五脏俱病。其病多上热下寒。外热内寒。何也。
天气通于肺。天气热。故肺热极。所以大渴引饮小便频数或遗尿气逆胸中痞闷。或衄血。心在上
焦火位。天气热。故心热极。所以心烦闷乱狂言谵语神识昏沉瞀不知人。或吐血饮冷舌黑面红口唇生疮。
脾为中州坤土。天气热则地中阳气恒浮而不降。地下无阳则寒。故脾土虚。所以鼻尖凉多痰肌肉削不
能食面黄四肢无力。或呕或泄中焦虚痞气倦怠。肝肾居下焦。地之分。天气热。阳气不降。地下无
阳故肝肾虚寒。所以腰重脚弱筋骨痛腿足寒厥。或吐蛔或吐沫。瘴病一作。五脏之症俱见。非若伤
寒之传经。传一经方见一经之症也。知此则
知伤寒汗吐下之法。不当施于瘴疟矣。而治瘴之法。当知升降浮沉则顺之。寒热温凉而逆之之理。
必使心肺之阳。降于下焦。俾下元温暖。下元者人身之根本也。温暖则根本固。根本固则邪热退。
诸病息矣。
有人问：像您所说的，伤寒是由于感受寒邪引起的，瘴疟是由于感受热邪引起的。那么北方寒冷之地多寒邪，伤寒应该是北方的疾病；南方炎热之地多热邪，瘴疟应该是南方的疾病吗？
我回答说：您的话也有道理。上古圣人确实有关于“异法方宜”（不同地区采用不同治疗方法）的论述。但是不能固执一端而不知变通。如果说北方患伤寒的病多，南方患瘴疟的病多，这是可以的；如果说北方没有瘴疟，南方没有伤寒，那就不对了。因为天道运行无常，假如北方暑热过多，秋天突然连续几天酷热，北方人感染这种气候，也大多会患上瘴病。同样，在广东南方地区，如果冬天突然连续几天大寒，而南方人平时很少受寒，若感染了这种寒气，也大多会患上伤寒。所以医生应当上察天时四季温凉寒热的变化，上明五运六气中司天、在泉的理论，下察各地风土人情的适宜之处，中辨患者平日的体质性情。根据病情决定宜凉宜热，诊察患者平日是什么脉象，再审察现在的病症。或是外感风寒暑湿，或是内伤饮食劳役及七情男女之疾，或是感受乖戾之气而成为瘴灼之病。要辨别病邪所在经络和脏腑，决定宜补、宜泻、宜吐、宜汗、宜温、宜和解。这样万无一失，才不愧称为医生。
至于人体，自胸膈至头部为上焦，其气象征着天；自胸膈至腹部为中焦，其气象征着人；自腹部至足部为下焦，其气象征着地。从五行理论来看，上焦属丙丁火，中焦属戊己土，下焦属壬癸水。在五脏方面，心、肺属阳，位居上部；脾属阴坤土，位居中部；肾、肝属阴，位居下部。必须做到阴能上升，阳能下降，从而形成水火既济、天地交泰的状态，这才是健康的人（平人）。如果在容易发生瘴病的地区，秋冬季节往往偏热，导致人体的阴阳之气，该上的在上，该下的在下，无法相交，从而形成水火未济、天地不交的“否”卦状态。因此，一旦触动外邪，五脏都会生病。这类病症多表现为上热下寒、外热内寒。为什么呢？天气通于肺，天气热，所以肺热极盛，出现极度口渴想喝水、小便频数甚至遗尿、气逆胸中痞闷、或鼻出血等症状。心位于上焦火位，天气热，所以心热极盛，出现心烦闷乱、狂言谵语、神识昏沉、昏迷不省人事、或吐血、喜饮冷水、舌苔黑、面色红、口唇生疮等症状。脾为中州坤土，天气热则地中阳气常浮越而不降，地下无阳则寒，所以脾土虚弱，出现鼻尖发凉、多痰、肌肉消瘦、不能进食、面色黄、四肢无力、或呕吐或腹泻、中焦虚痞、气短倦怠等症状。肝肾居于下焦地之分野，天气热，阳气不降，地下无阳，所以肝肾虚寒，出现腰部沉重、脚弱、筋骨疼痛、腿足寒冷厥逆、或吐蛔虫或吐涎沫等症状。瘴病一旦发作，五脏的症状都会出现，不像伤寒那样按经络依次传变，传一经才见一经的症状。懂得这个道理，就知道伤寒的汗、吐、下治法，不应当施用于瘴疟。而治疗瘴病的方法，应当知道“升降浮沉则顺之，寒热温凉而逆之”的道理。必须使心肺的阳气下降于下焦，使得下元温暖。下元是人身的根本，温暖则根本稳固，根本稳固则邪热退去，各种疾病也就平息了。
A person asked: "As you stated, Shanghan (Cold Damage) is caused by cold pathogenic factors, while Zhangmiao (Miasma Malaria) is caused by heat pathogenic factors. Therefore, since the North is predominantly cold, Shanghan should be a disease of the North; and since the South is predominantly hot, Zhangmiao should be a disease of the South, correct?"
I replied: "Your words have merit. The sages of antiquity indeed had discussions on 'Yi Fa Fang Yi' (Different Methods Suitable for Different Regions). However, one must not adhere rigidly to one view without flexibility. It is acceptable to say that there are more cases of Shanghan in the North and more cases of Zhangmiao in the South. But it is incorrect to claim that there is no Zhangmiao in the North or no Shanghan in the South. The laws of nature are unpredictable. For instance, if excessive summer heat occurs in the North, with sudden intense heat lasting several days in autumn, northerners contracting this climate may often suffer from miasma diseases. Conversely, in the southeast regions like Guangzhou, if severe cold lasts for several days in winter, and southerners who are accustomed to warmth contract this cold qi, they may also frequently suffer from Shanghan. Therefore, physicians must observe above the changes of warmth, coolness, cold, and heat across the four seasons according to heavenly timing; understand above the principles of Wu Yun Liu Qi (Five Movements and Six Qi), specifically Si Tian (Sovereign Heaven) and Zai Quan (Ruling Spring); observe below the local customs and environmental suitability of various regions; and discern within the patient's daily constitution and temperament. One must determine whether cooling or warming is appropriate, examine the pulse pattern during health, and then carefully assess the current illness. Whether it is an external contraction of Wind-Cold, Summer-Heat, or Dampness, or an internal injury due to diet, overwork, Seven Emotions, or sexual indiscretion, or a contraction of perverse qi leading to burning miasma, the physician must identify which Meridian and Zang-Fu Organ is affected, and decide whether tonification, purgation, emesis, diaphoresis, warming, or harmonization is indicated. Only by doing so can one achieve success in every case and truly deserve the title of physician.
Regarding the human body, from the chest and diaphragm up to the head is the Upper Jiao (Upper Burner), corresponding symbolically to Heaven; from the chest and diaphragm down to the abdomen is the Middle Jiao (Middle Burner), corresponding symbolically to Humanity; and from the abdomen down to the feet is the Lower Jiao (Lower Burner), corresponding symbolically to Earth. From the perspective of Five Elements theory, the Upper Jiao belongs to Bing-Ding Fire, the Middle Jiao belongs to Wu-Ji Earth, and the Lower Jiao belongs to Ren-Gui Water. Among the Zang Organs, the Heart and Lung are Yang and reside in the upper part; the Spleen is Yin Kun Earth and resides in the middle; the Kidney and Liver are Yin and reside in the lower part. Health requires Yin to ascend and Yang to descend, thereby achieving Shui Huo Ji Ji (Water and Fire Mutual Completion) and Tian Di Jiao Tai (Heaven and Earth Interaction), resulting in a state of a healthy person (Ping Ren). In regions prone to miasma, autumn and winter are often hot. This causes the Yin and Yang Qi of the human body to remain separated—upper staying upper, lower staying lower—resulting in Shui Huo Wei Ji (Water and Fire Not Completing) and Tian Di Bu Jiao Pi (Heaven and Earth Non-Interaction). Consequently, upon contact with external pathogens, all five Zang Organs become diseased. These illnesses often manifest as upper heat and lower cold, or external heat and internal cold. Why? Heavenly Qi connects to the Lung. When heavenly Qi is hot, Lung Heat becomes extreme, leading to extreme thirst with desire to drink, frequent urination or even enuresis, rebellious Qi causing chest fullness and oppression, or epistaxis. The Heart, located in the Fire position of the Upper Jiao, suffers extreme heat when heavenly Qi is hot, leading to mental restlessness, confusion, delirium, unconsciousness, hematemesis, preference for cold drinks, black tongue coating, red face, and sores on lips and mouth. The Spleen is the central Kun Earth. When heavenly Qi is hot, Yang Qi in the earth floats upward and fails to descend; lacking Yang below, it becomes cold, causing Spleen Earth deficiency. Symptoms include a cold nasal tip, excessive phlegm, muscle wasting, anorexia, yellow complexion, limb weakness, vomiting or diarrhea, middle-jiao deficiency bloating, and fatigue. The Liver and Kidney reside in the Lower Jiao, the domain of Earth. Due to hot heavenly Qi preventing Yang descent and the lack of Yang underground, the Liver and Kidney become deficient and cold. Symptoms include heavy waist, weak legs, bone and joint pain, cold and cold extremities in legs and feet, vomiting roundworms, or vomiting saliva. Once a miasma disease manifests, symptoms of all five Zang Organs appear simultaneously, unlike Shanghan which transmits through meridians sequentially, showing symptoms only of the currently affected meridian. Understanding this, one knows that the sweating, emetic, and purgative methods for Shanghan should not be applied to Zhangmiao. Instead, the treatment for Zhangmiao must follow the principle of 'following floating and sinking, and opposing cold and heat.' One must ensure that the Yang of the Heart and Lung descends to the Lower Jiao, warming the Xia Yuan (Root of the Lower Origin). The Xia Yuan is the root of the human body; when warm, the root is solid; when solid, evil heat retreats, and all diseases subside."