《难经》云∶虚则补母，实则泻子。此亦互文见义，以明补泻有活法，不必专执本脏也
。故
常有实泻母而虚补子者。仲景泻心汤中用大黄，却确是实则泻子之义。是火为土壅，湿热菀
结胸中，致火气不能遂其升降之用，发为喘满痞结者也。补泻母子，是因本脏不可直补直泻
，而委曲求全之法也。凡病须补泻兼到者，不能一脏而两施补泻也，则权母子而分施之。
燥屎为津液耗虚，肠胃枯结，而屎不得下，是阳之有余、阴之不足也；宿食为胃有寒湿
，水
谷久停不化，是阴之有余、阳之不足也。故仲景用承气治燥屎，以芒硝清热，大黄润燥，而
以枳、朴推其气使之下行。若宿食不得熟腐，必以干姜、豆蔻、山楂、麦芽温而化之矣。近
医燥屎、宿食不分，每以山楂、麦芽治燥屎，致愈坚而不得下；以大黄，芒硝下宿食，每致
洞泄完谷，阳脱而死。此等浅证，尚不能辨治，何以医为?
东垣以大便秘结，为血中伏火。此指常秘者言。又有卒秘于春分前后者，亦多因肝阳初
升，
伏火乍动所致。若卒秘于秋分前后，或夏月久旱暑盛之时，则多属肺气虚燥之故。暑燥既已
开泄肺气，而汗多又伤津液，加以口鼻呼吸亢气，遂致肺气不足以下降，津液不足以濡润大
肠，是为肺移燥于大肠，与血中伏火无涉。吾每以沙参、蒌根各用两许投之，其效甚捷，不
待用血药也。
《难经》说：虚证要补母脏，实证要泻子脏。这也是通过互文的手法来阐明补法和泻法有灵活运用的法则，不必专门拘泥于本脏的补泻。所以常有实证反而泻母脏、虚证反而补子脏的情况。张仲景在泻心汤中使用大黄，确实体现了“实则泻子”的含义。这是因为火气被土气壅滞，湿热郁结在胸中，导致火气不能正常发挥升降的作用，从而引发气喘、胀满、痞塞和结聚的症状。对母子两脏进行补泻，是因为本脏不宜直接进行补或泻，而采取的一种迂回周全的治疗办法。凡是疾病需要补法和泻法同时兼顾的，不能在同一脏上同时施用补泻，于是权衡母子关系，分别施治。
燥屎是由于津液耗损亏虚，肠胃干枯凝结，导致大便无法排出，这是阳气有余、阴气不足的表现；宿食是因为胃中有寒湿，水谷食物长时间停留无法消化，这是阴气有余、阳气不足的表现。所以张仲景用承气汤治疗燥屎，是用芒硝清热，大黄润燥，并用枳实、厚朴推动气机使其向下运行。如果是宿食不能熟腐消化，必须用干姜、豆蔻、山楂、麦芽等药物温性化解它。近代医生不区分燥屎和宿食，常用山楂、麦芽治疗燥屎，导致大便更加坚硬而无法排出；用大黄、芒硝攻下宿食，常常导致腹泻完谷不化，阳气脱失而死。这种浅显的病证，如果不能辨别和治疗，还做什么医生呢？
李东垣认为大便秘结是血中潜伏的火邪所致。这是针对习惯性便秘而言的。又有在春分前后突然发生便秘的，也多是因为肝阳刚开始升发，伏火突然活动所引起。如果在秋分前后突然便秘，或者在夏季长期干旱暑热旺盛的时候，则多属于肺气虚弱干燥的缘故。暑热燥邪已经开泄肺气，加上出汗多又损伤津液，再加上口鼻呼吸急促亢盛，致使肺气不足以向下肃降，津液不足以濡润大肠，这就是肺将燥邪移交给大肠，与血中的伏火无关。我每次用沙参、瓜蒌根各一两投药治疗，效果非常迅速，不需要使用活血类药物。
The *Nan Jing* (Classic of Difficult Issues) states: "For deficiency, tonify the mother; for excess, drain the child." This is also a rhetorical device to clarify that tonification and draining methods have flexible applications, and one should not rigidly adhere only to the direct tonification or draining of the affected Zang organ. Therefore, it is common to encounter cases where an excess condition is treated by draining the mother organ, and a deficiency condition is treated by tonifying the child organ. The use of Da Huang (Rhei Radix et Rhizoma) in Zhang Zhongjing's Xiexin Tang (Heart-Draining Decoction) indeed embodies the principle of "draining the child in excess conditions." This occurs because Fire Qi is obstructed by Earth Qi, with damp-heat stagnating and knotting in the chest, preventing the Fire Qi from performing its normal ascending and descending functions, thereby leading to wheezing, distension, fullness, palpable masses, and obstruction. Tonifying the mother and draining the child is a method employed when the primary Zang organ cannot be directly tonified or drained, serving as a roundabout approach to achieve completeness. In diseases requiring simultaneous tonification and draining, one cannot apply both methods to a single organ; thus, one weighs the mother-child relationship and applies them separately.
Dry stool results from the consumption and deficiency of body fluids, causing dryness and coagulation in the intestines and stomach, leading to the inability to pass stool; this represents an excess of Yang and a deficiency of Yin. Retained food results from cold-dampness in the Stomach, where water and grain remain stagnant for a long time without being digested; this represents an excess of Yin and a deficiency of Yang. Therefore, Zhang Zhongjing uses Chengqi Tang (Descending-the-Qi Decoction) to treat dry stool, employing Mang Xiao (Natrii Sulfas) to clear heat, Da Huang (Rhei Radix et Rhizoma) to moisten dryness, and Zhi Shi (Aurantii Fructus Immaturus) and Hou Po (Magnoliae Officinalis Cortex) to push the Qi downward. If retained food fails to undergo proper digestion and transformation, it must be resolved using warm agents such as Gan Jiang (Zingiberis Rhizoma), Dou Kou (Cardamomi Fructus), Shan Zha (Crataegi Fructus), and Mai Ya (Hordei Fructus Germinatus). Modern physicians fail to distinguish between dry stool and retained food; they often use Shan Zha and Mai Ya to treat dry stool, causing the stool to become harder and impossible to pass; they use Da Huang and Mang Xiao to purge retained food, often resulting in severe diarrhea with undigested food, loss of Yang Qi, and death. If one cannot differentiate and treat such superficial conditions, how can one claim to be a physician?
Li Dongyuan considers constipation to be caused by latent fire within the Blood. This refers to habitual constipation. There are also cases of sudden constipation occurring around the Spring Equinox, which are mostly caused by the initial rising of Liver Yang and the sudden movement of latent fire. However, if sudden constipation occurs around the Autumn Equinox, or during periods of prolonged drought and intense summer heat in midsummer, it mostly belongs to deficiency-dryness of Lung Qi. Summer heat and dryness have already dispersed Lung Qi, and excessive sweating further damages body fluids. Coupled with rapid and vigorous respiration through the mouth and nose, this leads to insufficient Lung Qi to descend and insufficient body fluids to moisten the Large Intestine. This is described as the Lung transferring dryness to the Large Intestine, unrelated to latent fire in the Blood. I often prescribe Sha Shen (Glehniae Radix) and Gua Lou Gen (Trichosanthis Radix), each in quantities of approximately 30 grams (one liang), with very rapid efficacy, without needing to use blood-invigorating herbs.