古人以脉上辨内外伤于人迎气口，人迎脉大于气口为外伤，气口脉大于人迎为内伤。此辨固是，但其
说有所未尽耳。外感风寒，皆有余之证，是从前客邪来也，其病必见于左手，左手主表，乃行阳二十五
度。内伤饮食及饮食不节，劳役过甚，皆不足之病也，必见于右手，右手主里，乃行阴二十五度。故外
感寒邪，则独左寸人迎脉浮紧，按之洪大；紧者、急甚于弦，是足太阳寒水之脉，按之洪大而有力，中见
手少阴心火之脉，丁与壬合，内显洪大，乃伤寒脉也。若外感风邪，则人迎脉缓，而大于气口一倍，或
二倍、三倍。内伤饮食，则右寸气口脉大于人迎一倍，伤之重者，过在少阴则两倍，太阴则三倍，此内
伤饮食之脉。若饮食不节，劳役过甚，则心脉变见于气口，是心火刑肺，其肝木挟心火之势亦来搏肺，经
云∶侮所不胜，寡于畏者是也。故气口脉急大而涩数，时一代而涩也。涩者，肺之本脉；代者，元气不
相接。脾胃不及之脉，洪大而数者，心脉刑肺也；急者，肝木挟心火而反克肺金也。若不甚劳役，惟右关
脾脉大而数，谓独大于五脉，数中显缓时一代也。如饮食不节，寒温失所，则先右关胃脉损弱，甚则隐
而不见，惟内显脾脉之大数微缓时一代也。宿食不消，则独右关脉沉而滑。经云，脉滑者，有宿食也。
以此辨之，岂不明白易见乎。但恐山野间卒无医者，何以诊候，故复说病证以辨之。
古人通过比较人迎脉和气口脉来辨别内伤与外感病。如果人迎脉的搏动强度大于气口脉，属于外感（外伤）；如果气口脉的搏动强度大于人迎脉，属于内伤。这种辨别方法固然正确，但其论述尚有不周全之处。
外感风寒，都属于邪气盛实的证候，这是由外来客邪引起的，其病变表现一定出现在左手。左手主表，对应阳气运行二十五度。内伤饮食及饮食不节制、过度劳累，都属于正气不足的病证，其病变表现一定出现在右手。右手主里，对应阴气运行二十五度。
因此，外感寒邪时，只有左寸人迎脉呈现浮紧之象，重按则洪大；“紧”脉比“弦”脉更为急迫，这是足太阳膀胱经寒水之脉的特征；重按时感觉洪大且有力，其中兼见手少阴心火之脉的特征，这是因为丁壬相合，内部显现出洪大的脉象，这就是伤寒的脉象。
如果是外感风邪，那么人迎脉缓，且比气口脉大一倍，或者两倍、三倍。
如果是内伤饮食，那么右寸气口脉比人迎脉大一倍；伤势较重者，涉及少阴经则大两倍，涉及太阴经则大三倍，这是内伤饮食的脉象。
如果是饮食不节制、过度劳累，那么心脉的变化会反映在气口上，这是心火克制肺金（心火刑肺），肝木挟带心火的势头也来冲击肺脏。医经说：“欺侮所不胜（即反向克制），是因为无所畏惧”，指的就是这种情况。所以气口脉表现为急大而涩数，时常出现代脉而兼涩象。“涩”脉是肺的本脉；“代”脉代表元气不能接续。
脾胃功能不及的脉象，若表现为洪大而数，是心脉克制肺金所致；若表现为急脉，是肝木挟带心火而反向克制肺金所致。
如果劳累不是很严重，只是右关脾脉大而数，称为独大于其他五部脉，在数的脉象中显现出缓象，时而出现代脉。
如果饮食不节制，寒温失调，那么先出现右关胃脉损伤减弱，严重时隐伏不见，只在内里显现出脾脉的大数微缓，时而出现代脉。
Ancient physicians distinguished between external injuries (external pathogenic factors) and internal injuries by comparing the Renying pulse (pulse at the carotid artery, representing Yang/exterior) and the Qikou pulse (radial pulse at the cun position, representing Yin/interior). If the Renying pulse is greater than the Qikou pulse, it indicates an external injury; if the Qikou pulse is greater than the Renying pulse, it indicates an internal injury. This distinction is indeed correct, but its explanation is not exhaustive.
External contraction of wind-cold constitutes a syndrome of excess, arising from invading pathogenic factors. The pathology must manifest on the left hand. The left hand governs the exterior and corresponds to the circulation of Yang for twenty-five degrees. Internal injury due to diet, irregular eating habits, or excessive labor constitutes a syndrome of deficiency. The pathology must manifest on the right hand. The right hand governs the interior and corresponds to the circulation of Yin for twenty-five degrees.
Therefore, when contracting cold pathogens externally, only the left Cun position of the Renying pulse appears floating and tight; upon heavy pressure, it becomes surging (Hong). "Tight" (Jin) is more urgent than "wiry" (Xian), which is the pulse of the Foot-Taiyang Bladder channel (Cold Water). Upon heavy pressure, it feels surging and forceful, revealing characteristics of the Hand-Shaoyin Heart channel (Fire). Due to the combination of Ding (Fire) and Ren (Water), a surging pulse manifests internally; this is the pulse of Shanghan (Cold Damage).
If contracting wind pathogens externally, the Renying pulse is moderate (Huan) and one, two, or three times greater than the Qikou pulse.
In cases of internal injury from diet, the right Cun position of the Qikou pulse is one time greater than the Renying pulse. In severe cases involving the Shaoyin channel, it is two times greater; in cases involving the Taiyin channel, it is three times greater. This is the pulse pattern of internal injury from diet.
In cases of irregular diet and excessive labor, the Heart pulse changes manifest at the Qikou position. This represents Heart Fire insulting Lung Metal (Heart Fire punishing the Lungs). The Liver Wood, carrying the momentum of Heart Fire, also attacks the Lungs. As the classics state: "Insulting what should not be insulted, because of lacking fear," refers to this mechanism. Thus, the Qikou pulse appears urgent, surging, choppy (Se), and rapid (Shu), occasionally presenting with a intermittent pulse (Dai) accompanied by choppieness. "Choppy" is the intrinsic pulse of the Lung; "Intermittent" indicates that Yuan Qi (Original Qi) fails to connect continuously.
If the Spleen and Stomach are deficient, and the pulse is surging and rapid, it is because the Heart pulse insults the Lungs. If the pulse is urgent, it is because Liver Wood, carrying Heart Fire, counter-attacks Lung Metal.
If the labor is not severe, only the right Guan position (Spleen pulse) appears surging and rapid, being uniquely greater than the other five positions. Within the rapid quality, a moderate quality may appear, occasionally showing an intermittent pulse.
If there is irregular diet and improper regulation of cold and heat, the right Guan position (Stomach pulse) first becomes damaged and weak. In severe cases, it may become hidden and invisible, revealing only the intrinsic Spleen pulse, which is surging, rapid, slightly moderate, and occasionally intermittent.
If food stagnation is not digested, only the right Guan pulse appears deep (Chen) and slippery (Hua). The classics state: "A slippery pulse indicates food stagnation."
By using these methods for differentiation, is it not clear and easy to see? However, fearing that in remote areas there might suddenly be no physician available for diagnosis, I further describe the symptoms to aid in differentiation.