凡劳疫伤饥之人，皆内伤不足者也。所谓邪气伤虚不伤实，同一理也。观《卫生方》云
∶北人寓广之地者，或往来广之途者，俱有阴阳相搏之患。然居者十病二三，途者十病八九
。正以居者安静，途者劳伤耳。《活人三昧》论瘴疟条云∶饮食有节，起居有常，则邪气不
能为害。彼道路崎岖，人烟疏阔，水浆不洁，酒灸多腥，饮食起居，未免乖度，况复有阴阳
相搏之气乎？故曰∶瘴气惟染劳役伤饥之人者此也。又凡居岭南者，必慎起居，节饮食，寡
欲清心，虽有风邪勿能害也。惟内境不出，则外境不入，此理之自然。其有感而病者，皆不
知所慎耳。
岭南既号炎方，而又濒海，地卑而土薄。炎方土薄，故阳燠之气常泄；濒海地卑，故阴
湿之气常盛，二气相搏，此寒热之气所由作也。阳气泄，故冬无霜雪，四时放花，人居其地
，气多上壅，肤多汗出，腠理不密，盖阳不反本而然。阴气盛，故晨夕雾昏，春夏淫雨，一
岁之间，蒸湿过半，三伏之内，反不甚热，盛夏连雨，即复凄寒，饮食、衣服、药食之类，
往往生醭，人居其间，类多中湿，肢体重倦，又多香港脚之疾。盖阴常偏胜而然，阴阳之气既
偏而相搏，故人亦因之而感受其寒热不齐之病也。又阳燠既泄，则使人本气不坚，阳不下降
，常浮于上，故病者多上脘郁闷，胸中虚烦。阴湿既盛，则使人下体多寒，阴不上升，常沉
而下，故病者多腰膝重疼，腿足寒厥。予观岭南瘴疾，证候虽或不一，然大抵阴阳各不升降
，上热下寒者，十有八九。况人身上本属阳，下本属阴，兹又感此阳燠阴湿不和之气，自多
上热下寒之证也。得病之因，正以阳气不固，每发寒热，身必大汗，又复投之以麻黄、金沸
、青龙等汤，再发其表，则旋踵受毙；甚者，又以胸中痞闷，用利药下之，病患下体既冷。
下之，则十无一生。若此者，医害之也。
其时余染瘴疾，全家特甚。余悉用温中固下，升降阴阳正气之药，十治十愈。二仆皆病
，胸中痞闷烦躁，昏不知人。一云∶愿得凉药清膈。余审其证，上热下寒，皆以生姜附子汤
冷温服之，即日皆醒，自言胸膈清凉，得凉药而然也，实不知附子也。翌日各与丹珠丸一粒
，令空心服之，遂能食粥，然后用正气、平胃等药，自尔遂得平安。更治十数人皆安。盖附
子用生姜煎，既能发散，以热攻热，又能导虚热向下焦，除宿冷，又能固接元气。若烦闷
者，放冷服之。若病烦躁，不好饮水，反畏冷不能饮者，皆其虚热，非真热也，宜服姜附汤
。沈存中治瘴用七枣汤，正与此同，亦一服而愈。有用术附汤而病愈甚，盖术附相济，能固
热气，不能发散，惟附子一味为最妙。或有脉证实非上热下寒而目黄赤者，不可用附子。脉
若浮洪而数，寒热往来，无汗，乃小柴胡汤证。若证有可疑，寒热不辨，宜服嘉禾散。若热
多者，冷服之。嘉禾散能调中气，升降阴阳，治下虚中满，疗四时瘟疫伤寒，使无变动，虽
伤暑及阳证伤寒，服之亦解。若或寒多，服之尤宜。服二三日，即寒热之证自判，然后随证
调治之，无不愈者。大抵岭南之地卑湿，又人食槟榔，多气疏而不实，四时汗出，不宜更用
汗药，此理甚明。亦有当汗下者，然终不多也，明者察之。
凡是因过度劳累、瘟疫感染或饥饿而受损的人，都属于内部正气不足的体质。这正如“邪气只伤害虚弱之人，不伤害强壮之人”的道理是一样的。
观察《卫生方》中的记载：北方人居住在岭南地区，或者往来于岭南路途的人，都会遭受阴阳之气相互搏结的祸患。然而，居住在当地的人十人中只有两三人患病，而在路途奔波的人十人中有八九人患病。这正是因为居住者生活安静，而奔波者劳损受伤的缘故。
《活人三昧》在论述瘴疟的条目中说：“饮食有节制，起居有规律，那么邪气就不能造成危害。”那些道路崎岖不平，人烟稀少，饮水和食物不洁净，酒食烧烤多腥味，饮食起居难免违背常度，况且还有阴阳相搏的气候之气呢？所以说：瘴气之所以只感染那些劳累役使、饥饿受损的人，原因就在这里。另外，凡是居住在岭南的人，必须谨慎对待起居，节制饮食，减少欲望，清静心神，即使有风邪侵袭也不能侵害身体。只要内部环境稳固，外部邪气就无法侵入，这是自然的道理。那些因此感病的人，都是不知道谨慎的缘故。
岭南既然被称为炎热的地方，又濒临大海，地势低洼且土壤浅薄。炎热之地土壤浅薄，所以阳热之气常常外泄；濒临大海地势低洼，所以阴湿之气常常强盛。这两种气相互搏结，这就是寒热之气产生的原因。阳气外泄，所以冬天没有霜雪，四季都开花，人居住在这里，气机容易上壅，皮肤容易出汗，腠理（毛孔）不致密，这是因为阳气不能回归根本所致。阴气强盛，所以早晚雾气昏暗，春夏季淫雨连绵，一年之中蒸腾潮湿的时间超过一半，在三伏天里，反而不太热，盛夏连续下雨，又会变得凄冷寒冷。饮食、衣服、药物等物品，往往会长出霉斑，人居住在其中，大多感受湿气，肢体沉重疲倦，又多患有香港脚（脚气病）的疾病。这是因为阴气常常偏胜所致。阴阳之气既然偏颇且相互搏结，所以人也因此感受寒热不均的疾病。
另外，阳热之气既已外泄，就会使人本元之气不坚固，阳气不能下降，常常浮越于上部，所以患者多有上脘部郁闷、心中虚烦的症状。阴湿之气既已强盛，就会使人下部多寒，阴气不能上升，常常沉陷于下部，所以患者多有腰膝沉重疼痛、腿足寒冷厥逆的症状。我观察岭南的瘴疾，证候虽然或许有所不同，但大抵是阴阳之气各自不能升降，表现为上热下寒的情况，十之八九。何况人体本身上部属阳，下部属阴，如今又感受这种阳热与阴湿不调和的气，自然多出现上热下寒的证候。
得病的原因，正是由于阳气不固，每次发作寒热时，身体必定大汗淋漓，如果此时再投用麻黄汤、金沸草散、青龙汤等发汗解表的药物，再次发散体表，病人很快就会死亡；更严重的，又因为胸中痞闷，使用泻下药攻下，病患下部本来已经寒冷，再用泻下药攻下，就十无一生。像这种情况，是医生害了病人。
当时我也染上了瘴疾，全家病情特别严重。我都使用温补中焦、固护下元、调理阴阳正气的药物，治疗十个都痊愈。我的两个仆人也都病了，胸中痞闷烦躁，昏迷不省人事。其中一个说：“希望得到凉药来清膈热。”我仔细审查他们的证候，发现是上热下寒，都用生姜附子汤，放至冷温后服用，当天他们都醒了，自己说胸膈清凉，以为是吃了凉药才这样的，实际上并不知道里面含有附子。第二天各给他们服一粒丹珠丸，令其空腹服用，于是能够喝粥，然后用正气散、平胃散等药物调理，从此便平安无事。我又治愈了十几个人，也都安康。大概附子配合生姜煎煮，既能发散，以热治热，又能引导虚热向下焦，去除宿存的寒气，又能固接元气。如果有烦闷症状的，放冷后服用。如果病人烦躁，不喜欢喝水，反而怕冷不能喝水的，这都是虚热，不是真热，适宜服用姜附汤。沈括（沈存中）治疗瘴疾使用七枣汤，与此方法相同，也是一服药就痊愈。有人使用术附汤却使病情加重，大概是因为白术和附子相辅相成，能固守热气，但不能发散，只有单用附子最为精妙。如果有脉象和证候确实不是上热下寒，而是眼睛发黄发红的，不可使用附子。如果脉象浮洪而数，寒热往来，无汗，这是小柴胡汤的证候。如果证候有可疑之处，寒热难以辨别，适宜服用嘉禾散。如果热象多的，冷服。嘉禾散能调和中气，升降阴阳，治疗下虚中满，疗治四季瘟疫伤寒，使其不发生变动，即使是伤暑及阳证伤寒，服用也能解除。如果寒象多，服用它尤其适宜。服用两三天后，寒热的证候自然分辨清楚，然后随证调理治疗，没有不痊愈的。大抵岭南之地势低洼潮湿，加上人们食用槟榔，多气疏而不实，四季出汗，不宜再使用发汗药，这个道理是很明显的。也有应当使用汗法或下法的，但最终占的比例不多，明智的人要仔细考察。
All those who are injured by overexertion, epidemic diseases, or hunger belong to the constitution of internal deficiency. This is consistent with the principle that "pathogenic factors only injure the deficient and do not injure the solid."
As observed in *Weisheng Fang* (Health Preservation Formulas): Northerners residing in Lingnan or traveling through its routes all suffer from the conflict between Yin and Yang Qi. However, among residents, only two or three out of ten fall ill, whereas among travelers, eight or nine out of ten fall ill. This is precisely because residents live quietly, while travelers suffer from exertion and injury.
*Liren Sanmi* (The Three Mysteries of Life), in its discussion on malarial fevers due to miasma, states: "If diet is regulated and daily routine is regular, pathogenic factors cannot cause harm." In areas where roads are rugged, population is sparse, water and food are unclean, and alcoholic beverages or roasted foods are often fishy, dietary habits and daily routines inevitably deviate from moderation. Moreover, there is the influence of conflicting Yin and Yang climatic Qi. Thus it is said: Miasma Qi infects only those who are exhausted by labor and injured by hunger for this reason. Furthermore, anyone residing in Lingnan must be cautious about their daily routine, moderate their diet, reduce desires, and keep the mind pure. Even if wind-pathogens invade, they cannot cause harm. When the internal environment remains stable, external pathogens cannot enter; this is a natural law. Those who become ill due to infection simply failed to exercise caution.
Lingnan is known as a hot region and borders the sea; the terrain is low, and the soil is shallow. In hot regions with shallow soil, Yang-warm Qi often dissipates outward; bordering the sea with low terrain, Yin-damp Qi often prevails. The conflict between these two Qi gives rise to cold and heat. Due to the dissipation of Yang Qi, there is no frost or snow in winter, and flowers bloom throughout the four seasons. People living there tend to have Qi stagnating upward and excessive sweating, leading to loose interstices (pores). This occurs because Yang Qi fails to return to its root. Due to the prevalence of Yin Qi, mornings and evenings are foggy, spring and summer bring incessant rain, and humid conditions persist for more than half the year. Even during the Sanfu days (the hottest period), it may not feel very hot; continuous rain in midsummer can make it chillingly cold. Food, clothing, and medicines often develop mold. People living in such environments mostly contract dampness, suffering from heavy limbs and fatigue, and frequently suffer from Hong Kong foot (Jiaoxi disease/foot rot). This results from the predominance of Yin Qi. Since Yin and Yang Qi are imbalanced and conflicting, people consequently contract diseases characterized by uneven cold and heat.
Furthermore, since Yang-warm Qi dissipates, the body's original Qi becomes insecure. Yang Qi fails to descend and floats upward, causing patients to experience oppression in the upper epigastrium and empty irritability in the chest. Since Yin-damp Qi prevails, the lower body becomes cold. Yin Qi fails to ascend and sinks downward, causing patients to experience heaviness and pain in the waist and knees, and coldness and cold extremities in the legs and feet. Observing miasma diseases in Lingnan, although symptoms may vary, the vast majority present as Shang Re Xia Han (Upper Heat and Lower Cold) due to the failure of Yin and Yang Qi to ascend and descend properly. Given that the human body naturally has Yang above and Yin below, contracting this discordant Qi of Yang-warmth and Yin-dampness naturally leads to Upper Heat and Lower Cold syndromes.
The cause of illness lies in the insecurity of Yang Qi. Each episode of chills and fever is accompanied by profuse sweating. If one then administers diaphoretic formulas such as Mahuang Tang (Ephedra Decoction), Jinfei Cao San (Boilweed Powder), or Qinglong Tang (Azure Dragon Decoction) to further release the exterior, the patient will die shortly thereafter. Worse still, if one uses purgatives for chest fullness and stuffiness in a patient whose lower body is already cold, death is inevitable. Such cases represent medical malpractice.
At that time, I contracted miasma disease, and my entire family suffered severely. I treated them all with herbs that warm the middle, secure the lower, and regulate the ascending and descending of correct Qi. All ten recovered. My two servants also fell ill, suffering from chest fullness, irritability, and unconsciousness. One requested cool herbs to clear the diaphragm. Upon careful examination, I determined the syndrome was Upper Heat and Lower Cold. I administered Shengjiang Fuzi Tang (Ginger and Aconite Decoction) cooled to lukewarm temperature. Both woke up the same day, reporting a cooling sensation in the chest and diaphragm, believing it was due to cool medicine, unaware that it contained Fuzi (Aconite Lateral Root). The next day, each took one pill of Danzhu Wan (Cinnabar Pill) on an empty stomach, enabling them to consume congee. Subsequently, using Zhengqi San (Upright Qi Powder) and Pingwei San (Peace the Stomach Powder), they recovered fully. I cured over ten others similarly. Fuzi decocted with ginger can disperse, treat heat with heat, guide deficient heat downward to eliminate old cold, and consolidate Yuan Qi. For those with irritability, it should be taken cool. For patients with irritability who dislike drinking water or fear cold liquids, this indicates deficient heat rather than true heat; Jiang Fu Tang (Ginger and Aconite Decoction) is appropriate. Shen Cunzhong (Shen Kuo) used Qizao Tang (Seven Jujube Decoction) to treat miasma, which is similar and effective after one dose. Some used Shufu Tang (Atractylodes and Aconite Decoction) but the condition worsened, likely because Atractylodes and Aconite together consolidate heat rather than disperse it. Only single-herb Fuzi is most excellent. However, if the pulse and syndrome clearly indicate non-Upper Heat/Lower-Cold patterns, such as yellow/red eyes, Fuzi should not be used. If the pulse is floating, surging, and rapid, with alternating chills and fever and no sweat, this is a Xiao Chaihu Tang (Minor Bupleurum Decoction) syndrome. If the syndrome is doubtful and chills/fever are indistinguishable, Jiahe San (Harmonizing Grain Powder) is suitable. If heat predominates, take it cool. Jiahe San regulates middle Qi, ascends and descends Yin and Yang, treats lower deficiency with middle fullness, and prevents changes in seasonal epidemics and cold damage. It resolves even heatstroke and Yang-type cold damage. It is especially suitable if cold predominates. After two to three doses, the nature of chills and fever becomes clear, allowing for symptomatic treatment without fail. Generally, Lingnan is low and damp, and people consume betel nut, which makes Qi diffuse but not solid. With sweating throughout the year, diaphoretics should not be used further; this logic is clear. Although some cases require diaphoresis or purgation, they are rare. Wise practitioners should observe this carefully.