二便皆脾胃之出路。小便是清道属气。大肠是浊道属血。失血家。血虚便燥。尤其应得。四物汤加麻仁主
之。血燥者加桃仁川军。气燥者加杏仁枳壳。风燥者加皂角白芷防风。火燥者宜加枳壳浓朴大黄芒硝。
大肠乃胃之关门。胃为燥土。若胃有燥屎而不下者。其责不在大肠。而在胃。其证口渴。手足潮热。或发谵
语。三一承气汤下之。或四物汤加麻仁枳壳浓朴大黄以滋降之。
又小便数而不禁。大便反闭者。名为脾约。谓脾津下泄。无以润肠故也。仲景用脾约丸治之。丹溪谓宜清
肺燥。肺清则小水有制。而脾得灌溉。宜用清燥救肺汤治之。
肾开窍于二阴。肾虚阴不足。无以润肠者。宜左归饮。加黑芝麻肉苁蓉治之。
肺与大肠相表里。肺遗热于大肠则便结。肺津不润则便结。肺气不降则便结。肺遗热者。人参泻肺汤治
之。肺津不润者。清燥救肺汤治之。肺气不降者。清燥救肺汤。合四磨汤。再重加杏仁。或少加葶苈子治之。
与便血条。合看自明。
此外又有瘀血闭结之证。或失血之后。血积未去。或跌打损伤。内有瘀血。停积不行。大便闭结。或时通利。
仍不多下。所下之粪。又带黑色。腹中时时刺痛。口渴发热。脉带涩象。宜用桃仁承气汤治之。或失笑散加
杏仁桃仁当归白芍。
大小便都是脾胃的排泄通道。小便属于清道，与气相关；大肠属于浊道，与血相关。失血的患者，由于血液亏虚导致大便干燥，这是必然会出现的情况，应当使用四物汤加火麻仁来主治。如果是血燥引起的，加入桃仁和川军（大黄）；如果是气燥引起的，加入杏仁和枳壳；如果是风燥引起的，加入皂角、白芷和防风；如果是火燥引起的，适宜加入枳壳、厚朴、大黄和芒硝。
大肠是胃的“关门”。胃属于燥土，如果胃中有燥结的粪便而不能下行，责任不在大肠，而在胃。其症状表现为口渴、手足定时发热，或者出现胡言乱语（谵语），应当用三一承气汤攻下。或者使用四物汤加火麻仁、枳壳、厚朴、大黄以滋养并通降。
另外，如果小便频数且不受控制，大便反而闭塞不通，这称为“脾约”。意思是脾的津液向下泄漏，没有足够的津液来滋润肠道。张仲景使用脾约丸治疗此症。朱丹溪认为应当清肺燥，肺脏清凉则小便有节制，脾脏得以灌溉滋润，适宜使用清燥救肺汤治疗。
肾开窍于前后二阴。肾虚且阴液不足，无法滋润肠道的，适宜使用左归饮，加黑芝麻和肉苁蓉治疗。
肺与大肠相表里。肺将热邪传给大肠会导致便秘；肺津不能滋润也会导致便秘；肺气不下降也会导致便秘。如果是肺遗热导致的，用人参泻肺汤治疗；如果是肺津不润导致的，用清燥救肺汤治疗；如果是肺气不降导致的，用清燥救肺汤合四磨汤，再加重杏仁用量，或少量加入葶苈子治疗。这与便血条目的内容结合来看，自然明白其中的道理。
此外还有瘀血闭结的证候。有的在失血之后，瘀血未去；有的因跌打损伤，体内有瘀血停滞不行，导致大便闭结。有时虽然能排便，但排出不多，所排出的粪便带有黑色，腹部时时感到刺痛，伴有口渴、发热，脉象带涩，适宜用桃仁承气汤治疗。或者使用失笑散加杏仁、桃仁、当归、白芍治疗。
Both urination and defecation are the exit pathways of the Spleen and Stomach. Urination belongs to the clear pathway and is associated with Qi (vital energy); the Large Intestine belongs to the turbid pathway and is associated with Blood. Patients who have suffered blood loss suffer from dry stools due to Blood deficiency, which is a natural consequence. The primary treatment should be Siwu Tang (Four Substances Decoction) added with Hemp Seed (Cannabis Fructus). If caused by Blood dryness, add Peach Kernel (Persicae Semen) and Rhubarb (Rhei Radix et Rhizoma). If caused by Qi dryness, add Apricot Kernel (Armeniacae Semen Amarum) and Immature Bitter Orange (Aurantii Fructus Immaturus). If caused by Wind dryness, add Gleditsia Sinensis Fruit (Gleditsiae Fructus), Angelica Dahurica Root (Angelicae Dahuricae Radix), and Saposhnikovia Divaricata Root (Saposhnikoviae Radix). If caused by Fire dryness, it is appropriate to add Immature Bitter Orange (Aurantii Fructus Immaturus), Magnolia Bark (Magnoliae Officinalis Cortex), Rhubarb (Rhei Radix et Rhizoma), and Mirabilite (Natrii Sulfas).
The Large Intestine serves as the "closing gate" of the Stomach. The Stomach is considered Dry Earth. If there are dry fecal masses in the Stomach that fail to descend, the responsibility lies not with the Large Intestine but with the Stomach. Symptoms include thirst, tidal fever of the hands and feet, or delirious speech (Zhenyu). It should be treated with San Yi Chengqi Tang (Three-One Purging Decoction) to purge the accumulation. Alternatively, Siwu Tang (Four Substances Decoction) added with Hemp Seed (Cannabis Fructus), Immature Bitter Orange (Aurantii Fructus Immaturus), Magnolia Bark (Magnoliae Officinalis Cortex), and Rhubarb (Rhei Radix et Rhizoma) can be used to nourish and descend.
Furthermore, if urination is frequent and involuntary, while defecation is conversely obstructed, this condition is named Pi Yue (Spleen Constraint). This implies that the fluids of the Spleen leak downward, leaving insufficient moisture to lubricate the intestines. Zhang Zhongjing used Pi Yue Wan (Spleen Constraint Pill) to treat this. Zhu Danxi suggested clearing Lung dryness; when the Lung is clear, urination becomes regulated, allowing the Spleen to receive irrigation. Qingzao Jiufei Tang (Clear Dryness and Rescue the Lung Decoction) is appropriate for treatment.
The Kidney opens into the two yin orifices (anterior and posterior). In cases of Kidney deficiency with insufficient Yin fluids failing to lubricate the intestines, Zuogui Yin (Left Restoring Decoction) added with Black Sesame Seed (Sesami Fructus Niger) and Cistanche Stem (Cistanches Herba) should be used.
The Lung and the Large Intestine are exteriorly-interiorly related. Heat transmitted from the Lung to the Large Intestine causes constipation; lack of Lung fluid lubrication causes constipation; failure of Lung Qi to descend causes constipation. For heat transmitted from the Lung, Renshen Xiefei Tang (Ginseng Draining Lung Decoction) is used. For lack of Lung fluid lubrication, Qingzao Jiufei Tang (Clear Dryness and Rescue the Lung Decoction) is used. For failure of Lung Qi to descend, Qingzao Jiufei Tang (Clear Dryness and Rescue the Lung Decoction) combined with Simo Tang (Four-Marrow Decoction), with increased dosage of Apricot Kernel (Armeniacae Semen Amarum) or a small amount of Lepidium Seed (Lepidii Semen), is used. This clarifies the matter when read together with the section on Hematochezia.
Additionally, there is the syndrome of constipation due to Blood stasis. This may occur after blood loss where stasis remains, or following traumatic injury where internal blood stasis accumulates and fails to move, leading to obstinate constipation. Although bowel movements may occasionally occur, the volume is small, and the excrement is black. There is often stabbing pain in the abdomen, accompanied by thirst, fever, and a choppy pulse. Tao Ren Chengqi Tang (Peach Kernel Purging Decoction) is indicated. Alternatively, Shixiao San (Frustrated Pain Powder) added with Apricot Kernel (Armeniacae Semen Amarum), Peach Kernel (Persicae Semen), Angelica Sinensis Root (Angelicae Sinensis Radix), and White Peony Root (Paeoniae Radix Alba) may be used.