东垣云。仲景论内外不足。发热自汗之证。大禁发汗。若饮食劳倦。杂病发热。自汗表虚之
证。认作有余。误用表药发之。汗大出而表益虚也。身尽热。先太阳也。从外而之内者为外伤。
手足不和。两胁俱热如火。先少阳也。从内而之外者为内伤。伤食令人头痛。脉数发热。但左手
脉平和。身不疼痛是也。人迎气口俱紧盛。或举按皆实大。发热而恶寒。腹不和而口液。此内外
俱伤也。夏月火乘土位。湿热相合。病多烦躁闷乱。四肢发热。或身体沉重。走注疼痛。皆湿热
相搏。郁而不伸。故致热也。发热身疼。而身如熏黄者。湿热也。一身尽痛发热。日晡所剧者。
风湿也。汗出而身热者。风热也。身热脉弦数。战栗而不恶寒者。瘅疟也。中脘有痰。令人憎寒
发热。恶风自汗。寸口脉浮。胸膈痞满。有类伤寒。但头不疼。项不强为异。虚烦与伤寒相似。
身热脉不浮紧。不恶寒。但热而烦。头不痛。香港脚为病。大便坚。脚膝两胫肿痛。或枯细者。当
其发时。亦发热憎寒呕恶。有似伤寒也。春夏之交。发热而渴。或微恶寒。右手脉来数盛者。温
病也。身热头疼。自汗多眠。阳脉浮滑。阴脉濡弱者。风温也。夏月大热而渴。脉盛躁者。热
病也。夏月脉虚。身热而喘乏者。伤暑也。四肢发热。口舌咽干。烦躁闷乱者。心与小肠之火。
乘脾土之位。脾主四
肢。为诸阳之本。脾热故四肢发热。每日晡时憎寒壮热。脉数盛而有痛处者。痈毒之将发也。
李士材治夏彝仲太夫人。年届八十。因彝仲远仕闽中。忧思成疾。忽发热头疼。医以伤寒发散
禁食。一剂而汗如浴。喘促神昏。其脉大无力。即令进食。而投参、 、白术、橘红、甘草、煨
姜。一剂而喘汗差减。倍用参、术至一两。证愈七八。惟食未强。此火衰不能生土。加熟附、干
姜。服二月而痊。
李东垣曾说，张仲景论述内伤不足和外感不足的病证时，对于发热、自汗的症状，严禁使用发汗法。如果是因饮食不节或劳倦过度引起的杂病发热、自汗等表虚证候，如果误认为是实证（有余），错误地使用解表药来发汗，会导致大汗淋漓从而使表气更加虚弱。
全身发热，且热势先从头部开始的是太阳经病变。热邪从外部侵入内部，属于外感伤风。手足不协调，两侧胁肋部都感觉像火一样灼热，这是少阳经病变。热邪从内部产生并向外发散，属于内伤。
伤食会导致头痛、脉象数而发热，但左手脉象平和，身体没有疼痛感，这就是伤食的表现。人迎穴和气口穴处的脉搏都紧盛，或者浮取沉取都显得实大，发热且怕冷，腹部不适且口中流涎，这是内外俱伤的表现。
夏季火热之气侵犯脾土之位，湿热相互结合，病症多表现为烦躁闷乱、四肢发热，或者身体沉重、游走性疼痛，这都是湿热相互搏结，郁滞而不能舒展，从而导致发热。
发热且身体疼痛，身体颜色像被烟熏过的黄色，这是湿热证。全身都疼痛且发热，在下午申酉时分（日晡）加重的，是风湿证。出汗后身体仍然发热，是风热证。身体发热、脉象弦数，出现寒战颤抖但不怕冷的，是瘅疟。
中脘部位有痰饮停滞，会导致憎寒发热、恶风自汗、寸口脉浮、胸膈痞满等症状，这些症状类似伤寒，只是头不痛、项背不强作为区别。虚烦证与伤寒相似，身体发热但脉象不浮紧，不怕冷，只是发热且心烦，头不痛。
香港脚（脚气病）发病时，大便干结，双脚膝盖和小腿肿痛，或者肌肉枯瘦细小。在其发作时，也会出现发热、憎寒、呕吐恶心等症状，看起来也像伤寒。
春夏交替之际，发热且口渴，或者轻微怕冷，右手脉象来势数而旺盛的，是温病。身体发热、头痛、自汗多眠，阳脉浮滑，阴脉濡弱的，是风温。夏季天气大热且口渴，脉象盛大躁动的，是热病。夏季脉象虚弱，身体发热且气喘乏力的，是伤暑。
四肢发热、口舌咽喉干燥、烦躁闷乱的，是心与小肠的火邪，乘袭脾土之位。因为脾主四肢，是诸阳之本，脾热所以导致四肢发热。每天下午申酉时分憎寒壮热，脉象数盛且有固定痛处的，是痈毒即将发作的表现。
李士材治疗夏彝仲太夫人的案例：患者年近八十，因为儿子夏彝仲远赴福建做官，忧思成疾。忽然出现发热、头痛，医生按照伤寒发散的方法治疗并禁止进食，服用一剂药后大汗淋漓如洗澡一般，随后出现喘促、神志昏迷。其脉象大而无力，李士材立即让她进食，并投用人参、[此处原文缺字，推测为茯苓或类似健脾药，依上下文补译逻辑]、白术、橘红、甘草、煨姜。服用一剂后，喘促和出汗症状减轻，加倍使用人参、白术至一两，病情痊愈七八成，只是食欲尚未完全恢复。这是因为命门火衰不能生脾土，于是加入熟附子、干姜，服用两个月后痊愈。
Li Dongyuan stated that Zhang Zhongjing discussed the conditions of internal deficiency and external insufficiency. For symptoms such as fever and spontaneous sweating, diaphoresis (sweating-inducing therapy) is strictly prohibited. If a miscellaneous disease causes fever and spontaneous sweating due to improper diet or overexertion, presenting as a superficial deficiency syndrome, mistaking it for an excess condition and erroneously using exterior-releasing drugs to induce sweating will result in profuse sweating, thereby further weakening the exterior Qi.
Generalized heat, starting first from the head, indicates a Taiyang (Greater Yang) meridian pathology. Heat entering from the outside to the inside constitutes an external injury (exogenous pathogen). Disharmony of the hands and feet, with intense heat in both hypochondriac regions like fire, indicates a Shaoyang (Lesser Yang) meridian pathology. Heat arising from the inside and radiating outward constitutes an internal injury.
Food stagnation causes headache, rapid pulse, and fever, but the left-hand pulse remains peaceful, and there is no body pain; this characterizes food stagnation. When both the Renying (ST9) and Qikou (LU9) pulses are tight and vigorous, or feel solid and large upon both lifting and pressing, accompanied by fever, aversion to cold, abdominal discomfort, and drooling, it indicates simultaneous external and internal injury.
In summer, Fire Qi invades the Earth position (Spleen/Stomach), where dampness and heat combine. Symptoms often include irritability, restlessness, heat in the four limbs, heavy body, or migrating pain. These arise from damp-heat clashing and stagnating without being able to extend, thus causing fever.
Fever with body ache, and a body color resembling smoke-stained yellow, indicates damp-heat. Generalized body pain with fever, worsening during the Shen-You hours (3 PM - 7 PM), indicates wind-dampness. Body heat persisting after sweating indicates wind-heat. Fever with a wiry and rapid pulse, tremors/chills without aversion to cold, indicates Dan-Nue (Malaria with high fever).
Phlegm retention in the Zhongwan (CV12) region causes aversion to cold, fever, aversion to wind, spontaneous sweating, floating pulse at the Cunkou (radial artery), and chest/epigastric fullness. These resemble Shanghan (Cold Damage), distinguished by the absence of headache and neck stiffness. Xu-Fan (Deficiency Irritability) resembles Shanghan: body heat without a floating-tight pulse, no aversion to cold, only heat and irritability, and no headache.
Hongxiangjiao (Jiaogong/Feet Coldness/Gout-like condition) presents with hard stool, swelling and pain in the feet, knees, and shins, or emaciation of these areas. During attacks, it also manifests with fever, aversion to cold, vomiting, and nausea, resembling Shanghan.
At the transition between spring and summer, fever with thirst, or slight aversion to cold, with a rapid and vigorous right-hand pulse, indicates Wenbing (Warm Disease). Body heat, headache, spontaneous sweating, and excessive sleepiness, with a floating-slippery Yang pulse and a soggy-weak Yin pulse, indicate Fengwen (Wind-Warmth). In summer, extreme heat with thirst and a盛大-vigorous/restless pulse indicates Rebing (Heat Disease). A weak pulse with fever and panting/laborious breathing in summer indicates Shanggong (Summerheat Injury).
Heat in the four limbs, dry mouth/tongue/throat, and irritability/restlessness indicate Fire of the Heart and Small Intestine invading the Spleen Earth position. Since the Spleen governs the four limbs and is the root of all Yang meridians, Spleen heat causes heat in the four limbs. Daily aversion to cold and severe fever during the Shen-You hours, with a rapid-vigorous pulse and fixed pain, indicates the impending eruption of Yongdu (Carbuncle/Pus-toxin).
Case Study: Li Shicai treated the elderly lady of Xia Yizhong. Approaching eighty years old, she fell ill due to worry and thinking caused by her son Xia Yizhong serving far away in Fujian. She suddenly developed fever and headache. Physicians treated it as Shanghan with dispersing methods and forbade food intake. After one dose, she sweated profusely like a bath, followed by panting and coma. Her pulse was large but powerless. Li immediately ordered her to eat and prescribed Renshen (Ginseng Radix et Rhizoma), [missing herb in text, context implies spleen-tonifying], Baizhu (Atractylodis Macrocephalae Rhizoma), Juhong (Citri Reticulatae Pericarpium Rubrum), Gancao (Glycyrrhizae Radix et Rhizoma), and Wei Jiang (Zingiberis Rhizoma Preparatum). After one dose, panting and sweating decreased. Doubling the dosage of Renshen and Baizhu to one liang, her condition improved by seventy to eighty percent, though appetite remained poor. This indicated Mingmen Fire deficiency failing to generate Earth (Spleen). He added Shu Fuzi (Aconiti Lateralis Radix Praeparata) and Ganjiang (Zingiberis Rhizoma). After two months of medication, she recovered completely.