外感内伤证候相类，治法悬绝，不可不辨。伤于饮食劳役，七情六欲为内伤；伤于
风寒暑湿为外感。内伤发热，时热时止∶外感发热，热甚不休。内伤恶寒，得暖便解；
外感恶寒，虽浓衣烈火不除。内伤恶风，不畏甚风，反畏隙风；外感恶风，见风便恶。
内伤头痛，乍痛乍止；外感头痛，连痛无停，直待表邪传里方罢。内伤有湿，或不作
渴，或心火乘肺，亦作燥渴∶外感须二三日外，表热传里，口方作渴。内伤则热伤气，
四肢沉困无力，倦忌嗜卧；外感则风伤筋，寒伤骨，一身筋骨疼痛；内伤则短气不足以
息。外感则喘壅气盛有余；内伤则手心热。外感则手背热，天气通于肺，鼻者，肺之外
候；外感伤寒则鼻塞，伤风则流涕。然能饮食，口知味，腹中和，二便如常，地气通于
脾，口者，脾之外候，内伤则懒言恶食，口不知味，小便黄赤，大便或秘或溏，左人迎
脉主表。外感则人迎大于气口，有气口脉主里；内伤则气口大于人迎。内伤证属不足，
宜温宜补宜和；外感证属有余，宜汗宜吐宜下。若内伤之症，误作外感，妄发其表，重
虚元气，祸如反掌，故立补中益气汤主之。又有内伤外感兼病者。若内伤重者，宜补养
为先，外感重者，宜发散为急。此汤惟上焦痰呕，中焦湿热，伤食膈满者，不宜服。
内伤之脉，右寸关必大，然初诊似滑，久按即软而无力，左脉平和不数，亦有弱
者，但小于右手耳，乃气弱火盛之脉，数大为虚火，无力为气弱，若误作有余之火，妄
用寒凉，则中气愈伤，火转甚矣。又有误为气口紧盛，作食滞者，然脉有力无力，已相
迥别，况宿滞者，必恶心饱闷，神壮不倦。内伤者，必不痞不饱，倦怠无力，懒于言
语，更可验也。
外感与内伤的证候表现相似，但治疗方法截然不同，必须加以辨别。因饮食不节、过度劳累以及七情六欲所伤，属于内伤；因风寒暑湿等外邪侵袭所伤，属于外感。
内伤引起的发热，是时而发热、时而停止；外感引起的发热，则是高热持续不退。内伤导致的恶寒（怕冷），遇到温暖即可缓解；外感导致的恶寒，即使穿着厚衣、靠近烈火也无法消除。内伤导致的恶风（怕风），并不畏惧大风，反而畏惧缝隙中透出的穿堂风；外感导致的恶风，只要见到风就会感到厌恶。内伤引起的头痛，是时痛时止；外感引起的头痛，是连续疼痛不停歇，直到表邪传入体内才会停止。
内伤伴有湿气，可能不口渴，或者因为心火乘袭肺金，也出现干燥口渴；外感则需经过两三天后，表热传入体内，口中才会产生渴感。内伤会导致热邪损伤元气，四肢沉重困倦无力，疲倦嗜睡；外感则风邪损伤筋脉，寒邪损伤骨骼，全身筋骨疼痛；内伤会导致气短，呼吸不足以接续。外感则表现为气喘、气息壅盛且有余；内伤则手心发热。外感则手背发热。天气通应于肺，鼻是肺的外在征候；外感伤寒则鼻塞，伤风则流鼻涕。
如果患者能正常饮食，口知滋味，腹部调和，大小便正常，这是地气通应于脾，口是脾的外在征候；内伤则懒言、厌恶进食，口不知滋味，小便黄赤，大便或便秘或溏泄。左人迎脉主要主表证。外感则人迎脉大于气口脉；右气口脉主要主里证；内伤则气口脉大于人迎脉。
内伤证属于正气不足，适宜用温补、调和的方法治疗；外感证属于邪气有余，适宜用发汗、催吐、泻下的方法治疗。如果是内伤的病症，误当作外感治疗，妄用发汗解表之法，会进一步耗损元气，灾祸立至，因此确立补中益气汤作为主治方剂。又有内伤与外感同时患病的。如果内伤严重，应以补养为先；外感严重，应以发散为急务。此汤（补中益气汤）仅适用于上焦有痰呕、中焦有湿热、伤食导致膈部胀满者不宜服用。
内伤的脉象，右寸关脉必然盛大，但初诊时似乎滑利，久按则软弱无力；左脉平和而不数急，也有微弱的，只是比右手脉小罢了，这是气弱火盛的脉象，数大是因为虚火，无力是因为气弱。如果误认为是实火，妄用寒凉药物，则中气更加受损，火势反而更旺。又有将脉象误认为气口紧盛，当作食积停滞的，然而脉象有力无力已经截然不同，况且宿食停滞者，必定恶心、饱闷，精神亢奋不知疲倦。内伤者，必定没有痞塞和饱闷感，而是倦怠无力，懒于言语，这更可验证。
The clinical manifestations of exterior contraction (Wai Gan) and interior injury (Nei Shang) are similar, yet their treatment principles are vastly different; thus, they must be carefully distinguished. Injury caused by improper diet, overexertion, and the seven emotions and six desires constitutes interior injury; injury caused by wind, cold, summer-heat, and dampness constitutes exterior contraction.
Fever due to interior injury is intermittent, appearing and disappearing; fever due to exterior contraction is high-grade and continuous without cessation. Chills (E Han) due to interior injury resolve upon warming; chills due to exterior contraction persist even with thick clothing and proximity to fire. Wind aversion (E Feng) due to interior injury does not fear strong winds but rather fears drafts from cracks; wind aversion due to exterior contraction causes aversion upon merely seeing wind. Headache due to interior injury comes and goes; headache due to exterior contraction is continuous and unceasing until the exterior pathogenic factor transmits inward.
Interior injury accompanied by dampness may present without thirst, or if heart fire invades the lung metal, it may present with dry thirst; exterior contraction requires two to three days for the exterior heat to transmit inward before thirst arises. Interior injury leads to heat damaging qi, resulting in heavy, fatigued limbs, weakness, and a desire to lie down; exterior contraction involves wind damaging sinews and cold damaging bones, causing pain throughout the body's sinews and bones. Interior injury leads to shortness of breath and insufficient respiration. Exterior contraction presents with panting, qi congestion, and excessiveness. Interior injury manifests as heat in the palms; exterior contraction manifests as heat on the dorsum of the hands. Heaven's qi connects with the lungs; the nose is the external manifestation of the lungs; exterior contraction of cold damage results in nasal congestion, while wind damage results in runny nose.
If one can eat and drink normally, taste food properly, feel harmony in the abdomen, and have normal urination and defecation, this indicates Earth's qi connecting with the spleen; the mouth is the external manifestation of the spleen. Interior injury results in reluctance to speak, aversion to eating, loss of taste, yellow-red urine, and either constipation or loose stools. The Renying pulse at the left neck primarily governs exterior syndromes. In exterior contraction, the Renying pulse is larger than the Qikou pulse; the Qikou pulse at the right wrist primarily governs interior syndromes. In interior injury, the Qikou pulse is larger than the Renying pulse.
Interior injury syndromes belong to deficiency, requiring warming, tonifying, and harmonizing methods; exterior contraction syndromes belong to excess, requiring diaphoretic, emetic, and purgative methods. If interior injury symptoms are mistaken for exterior contraction and treated with reckless sweating to release the exterior, vital qi will be further depleted, leading to disaster swiftly. Therefore, Buzhong Yiqi Tang (Tonify the Middle and Augment the Qi Decoction) is established as the primary formula. There are also cases where interior injury and exterior contraction coexist. If interior injury is severe, tonification and nourishment should take precedence; if exterior contraction is severe, dispersing and releasing the exterior is urgent. This decoction (Buzhong Yiqi Tang) is not suitable for patients with phlegm and vomiting in the upper jiao, damp-heat in the middle jiao, or food stagnation causing fullness in the chest/diaphragm.
The pulse of interior injury: the Cun and Guan positions on the right hand are necessarily large, but initially appearing slippery, they become soft and forceless upon prolonged pressing; the left pulse is peaceful and not rapid, though sometimes weak, just smaller than the right hand pulse. This is a pulse of weak qi and flourishing fire; rapidity and largeness indicate deficient fire, while forcelessness indicates weak qi. Mistaking this for excess fire and recklessly using cold-cooling herbs will further injure middle qi, causing the fire to intensify. Some may mistake the tight and vigorous Qikou pulse for food stagnation. However, the distinction between forceful and forceless pulses is already clear. Moreover, those with retained food stagnation must experience nausea, fullness, and hyperactive spirit without fatigue. Those with interior injury must not experience epigastric stuffiness or fullness, but rather fatigue, weakness, and reluctance to speak, which serves as further verification.