内证头痛，有时而作，有时而止；外证头痛，常常有之，直须传入里实方罢。此又内外证之不同者也。
内伤等病，是心肺之气已绝于外，必怠惰嗜卧，四肢沉困不收，此乃热伤元气。脾主四肢，既为热
所乘，无气以动。经云∶“热伤气”。又云∶热则骨消筋缓。此之谓也。若外伤风寒，是肾肝之气已绝于
内。肾主骨，为寒；肝主筋，为风。自古肾肝之病同一治，以其递相维持也，故经言胆主筋，膀胱主骨
是也。或中风，或伤寒，得病之日，便着床枕，非扶不起，筋骨为之疼痛，不能动摇，乃形质之伤。经
云∶“寒伤形”。又云∶“寒则筋挛骨痛”。此之谓也。
辨外伤不恶食，若劳役饮食失节，寒温不适，此三者皆恶食。
仲景《伤寒论》云，中风能食，伤寒不能食，二者皆口中和而不恶食。若劳役所伤及饮食失节、寒温
不适三者，俱恶食，口不知五味，亦不知五谷之味。只此一辨，足以分内外有余不足二证也。伤寒证虽不
能食，而不恶食，口中和，知五味，亦知谷味，盖无内证，则心气和，脾气通，知五谷之味矣。
外感风寒之邪，三日已外，谷消水去，邪气传里，始有渴也。内伤饮食失节，劳役久病者，必不
渴，是邪气在血脉中有余故也。初劳役形质，饮食失节，伤之重者，必有渴，以其心火炽，上克于肺金，
故渴也。又当以此辨之。虽渴欲饮冷水者，当徐徐少与之，不可纵意而饮，恐水多峻下，则胃气愈弱，
轻则为胀，重则传变诸疾，必反复闷乱，百脉不安，夜加增剧，不得安卧，不可不预度也。
内伤引起的头痛，有时发作，有时停止；外感引起的头痛，常常存在，直到病邪传入里实阶段才会停止。这是内证与外证的不同之处。
内伤类疾病，是心肺之气在外已衰竭，必然出现倦怠嗜睡、四肢沉重困倦无法收持的症状，这是因为热邪损伤了元气。脾主四肢，既然被热邪所乘，便没有气力来推动肢体。医经说：“热邪损伤气机。”又说：“热则导致骨骼消耗、筋脉松弛。”说的就是这种情况。如果是外感风寒，则是肾肝之气在内已衰竭。肾主骨，受寒邪影响；肝主筋，受风邪影响。自古以来，肾和肝的病证治疗原则相同，因为它们相互维持关系，所以医经说胆主筋、膀胱主骨也是这个道理。或者是中风，或者是伤寒，在得病当天，就卧床不起，不扶起来就不能动，筋骨疼痛，不能活动，这是形体质地的损伤。医经说：“寒邪损伤形体。”又说：“寒则导致筋脉拘挛、骨骼疼痛。”说的就是这种情况。
辨别外伤（外感）不厌恶进食，如果是劳役过度、饮食失节、寒温不适这三者，都会厌恶进食。
张仲景《伤寒论》中说，中风能进食，伤寒不能进食，但这两种情况口中都调和而不厌恶食物。如果是劳役所伤以及饮食失节、寒温不适这三种情况，都厌恶进食，口中不知五味，也不知道五谷的味道。仅凭这一点辨别，足以区分内伤不足和外感有余两种证候。伤寒证虽然不能进食，但并不厌恶食物，口中调和，知道五味，也知道谷物的味道，这是因为没有内伤证候，心气平和，脾气通畅，所以能感知五谷的味道。
外感风寒之邪，三天以后，谷物消化、水液代谢正常后，如果邪气传入里部，才开始出现口渴。内伤于饮食失节、劳役久病的人，一定不口渴，这是因为邪气在血脉中有余的缘故。刚开始劳役形体、饮食失节，受伤较重的，一定会口渴，因为心火炽盛，向上克制肺金，所以口渴。也应当以此加以辨别。即使口渴想喝冷水，也应该慢慢地少量给予，不可放纵意愿大量饮用，恐怕水多急剧下行，会使胃气更加虚弱，轻则导致腹胀，重则传变出各种疾病，必定反复烦闷扰乱，百脉不安，夜间症状加重，无法安卧，不可以不预先考量。
Headache caused by internal injury occurs intermittently, sometimes appearing and sometimes ceasing; headache caused by external contraction is persistent, continuing only until the pathogen transmits to the interior excess stage. This illustrates the difference between internal and external conditions.
In diseases of internal injury, the Qi of the Heart and Lung has already exhausted at the exterior, inevitably leading to lethargy and a desire to lie down, along with heaviness and weakness in the four limbs that cannot be sustained. This is due to Heat damaging the Yuan Qi (Original Qi). The Spleen governs the four limbs; once attacked by Heat, there is no Qi to move them. The Classics state: "Heat damages Qi." It also states: "Heat causes bone emaciation and tendon laxity." This refers to such cases. If it is an external contraction of Wind-Cold, then the Qi of the Kidney and Liver has already exhausted within. The Kidney governs bones and is affected by Cold; the Liver governs tendons and is affected by Wind. Since ancient times, diseases of the Kidney and Liver have been treated similarly because they mutually support each other; thus, the Classics mention that the Gallbladder governs tendons and the Bladder governs bones for this reason. Whether it is Wind-Stroke or Cold Damage, on the day of onset, the patient is bedridden, unable to rise without assistance, suffering from pain in the sinews and bones, and unable to move. This is damage to the physical structure. The Classics state: "Cold damages the form." It also states: "Cold causes sinew spasm and bone pain." This refers to such cases.
To distinguish external contraction from non-aversion to food: if it is due to overexertion, irregular diet, or inappropriate temperature regulation, all three lead to aversion to food. Zhang Zhongjing's *Treatise on Cold Damage* states that patients with Wind-Strike can eat, while those with Cold Damage cannot, but in both cases, the mouth feels harmonious and there is no aversion to food. However, in cases of injury from overexertion, irregular diet, or inappropriate temperature regulation, there is aversion to food, the mouth loses its sense of the five flavors, and one does not perceive the taste of grains. This single distinction is sufficient to differentiate between the two syndromes of internal deficiency and external excess. Although patients with Cold Damage may not be able to eat, they do not have an aversion to food; their mouths feel harmonious, they know the five flavors, and they perceive the taste of grains. This is because, without internal injury, the Heart Qi is peaceful and the Spleen Qi is unobstructed, allowing perception of the taste of grains.
When external Wind-Cold pathogens persist beyond three days, after grain digestion and water metabolism normalize, thirst begins only when the pathogen transmits to the interior. Patients with internal injury from irregular diet, chronic overexertion, or prolonged illness will definitely not experience thirst, as this indicates excess pathogen in the blood vessels. In initial stages of physical overexertion and dietary irregularity, if the injury is severe, thirst will definitely occur because Heart Fire becomes blazing and attacks Metal of the Lung upward, causing thirst. This should also be used for differentiation. Even if the patient desires cold water, it should be given slowly and in small amounts. One must not allow unrestricted drinking, lest excessive water cause rapid downward purging, further weakening Stomach Qi. Mildly, this leads to abdominal distension; severely, it transforms into various diseases, causing recurrent restlessness and agitation, discomfort in the hundred vessels, worsening symptoms at night, inability to sleep peacefully, and these consequences must be anticipated in advance.