大通，泻经隧水湿
苦寒有毒。能泻肾经及隧道水湿，直达水气所结之处，以攻决为用，为下水之圣药（仲
景大陷肠汤用之）。
主十二种水，大腹肿满（名水蛊。喻嘉言曰∶肾为水谷之海，五脏六腑之源。脾不能散
胃之水精于肺，而病于中；肺不能通胃之水道于膀胱，而病于上。肾不能司胃之关，时其输
泄，而病于下，以致积水浸淫，无所底止。肾者，胃之关也。前阴利水，后阴利谷。王好古
曰∶水者，脾肺肾三经所主。有五脏六腑十二经之部分，上头面，中四肢，下腰脚，外皮肤
，中肌肉，内筋骨。脉有尺寸之殊，浮沉之别，不可轻泻药，当知病在何经何脏，方可用之。
按∶水肿有痰裹食和瘀血、致清不升浊不降而成者，有湿热相生、隧道阻塞而成者；有燥热
冲击、秘结不通而成者，证属有余。有服寒凉伤饮食、中气虚衰而成者；有大病后正气衰惫
而成者，有小便不通、水液妄行、脾莫能制而成者，证属不足。宜
分别治之。然其源多由中气不足而起。丹溪曰∶水病当以健脾为主，使脾实而气运，则水
自行。宜参、苓为君，视所挟证加减，苟徒用利水药，多致不救），瘕疝积聚，留饮宿食，
痰迷癫痫。虚者忌用。
皮赤肉白，根作连珠。重实者良。面裹煨熟用（或用甘草、荠 汁浸三日，其水如墨，
以清为度，再面裹煨）。瓜蒂为使。恶远志。反甘草（张仲景治心下留饮，与甘草同用，取
其相反以立功也。有治水肿及肿毒者，以甘遂末敷肿处，浓煎甘草汤服之，其肿立消，二物
相反，感应如此）。
其味苦，性寒，有毒。能够泻除肾经及人体隧道（指体内深层的水液运行通道）中的水湿，药力直达水气凝结之处，以攻逐决裂水邪为主要作用，是下水利水的圣药（张仲景的大陷胸汤中使用了它）。
主治十二种水病，以及腹部大肿胀满（称为水蛊。喻嘉言说：肾是水谷汇聚之海，也是五脏六腑的源头。如果脾不能将胃吸收的水谷精微散布到肺，就会在中焦发病；如果肺不能将胃的水道通调至膀胱，就会在上焦发病；如果肾不能主管胃的关隘，及时调节排泄，就会在下焦发病，导致积水浸淫，没有止境。肾，就是胃的关隘。前阴负责利水，后阴负责利谷。王好古说：水液代谢由脾、肺、肾三经所主。水液病变可涉及五脏六腑和十二经脉的各个部分，上至头面，中至四肢，下至腰脚，外达皮肤，内入肌肉，深入筋骨。脉象有寸尺的不同，浮沉的区别，不可轻易使用泻下药，必须知道病在何经何脏，才能用药。按语：水肿有因痰浊裹挟饮食停滞和瘀血，导致清阳不升、浊阴不降而形成的，属于实证；有因湿热相生、隧道阻塞而形成的，也属实证；有因燥热冲击、便秘不通而形成的，亦属实证。也有因服用寒凉药物损伤饮食、中气虚衰而形成的；有大病之后正气衰惫而形成的；有小便不通、水液妄行、脾脏无法制约而形成的，这些属于虚证。应当分别治疗。然而其根源多由中气不足引起。朱丹溪说：治疗水病应当以健脾为主，使脾土坚实而气机运转，则水液自然自行消散。宜用人参、茯苓作为君药，根据兼夹症状加减，如果单纯使用利水药，大多会导致病情恶化甚至死亡），瘕疝积聚，留饮宿食，痰迷心窍导致的癫痫。体质虚弱者忌用。
甘遂皮呈赤色，肉质白色，根部呈连珠状。质地沉重坚实的为佳。外用或内服时需用面粉包裹煨熟后使用（或者用甘草、荠菜汁浸泡三天，泡出的水像墨汁一样黑，以水变清为度，再用面粉包裹煨熟）。瓜蒂可作为引经药。畏远志。反甘草（张仲景治疗心下留饮，与甘草同用，取其相反相成的道理以立功。有的治疗水肿及肿毒的案例中，用甘遂末敷于肿处，浓煎甘草汤内服，肿胀立即消退，两药相反，感应如此强烈）。
Gansui (Kansui Radix) promotes bowel movement and drains water-dampness from the meridians and collaterals.
It is bitter, cold, and toxic. It can drain water-dampness from the Kidney meridian and the body's deep channels (referring to the deep pathways for fluid metabolism), reaching directly to the sites where water qi condenses. Its primary function is to attack and resolve water accumulation, making it a supreme medicine for purging water (used in Zhang Zhongjing's Da Xianxiong Tang).
It treats twelve types of water diseases and severe abdominal distension and swelling (known as Shuigu [Water Gu]). Yu Jiayan stated: "The Kidney is the sea of food and drink and the source of the five zang and six fu organs. If the Spleen fails to scatter the water essence from the Stomach to the Lung, disease arises in the middle; if the Lung fails to regulate the water passages from the Stomach to the Bladder, disease arises in the upper jiao; if the Kidney fails to control the gate of the Stomach and timely regulate excretion, disease arises in the lower jiao, leading to overflowing accumulated water without cessation. The Kidney is the gate of the Stomach. The anterior orifice benefits water, while the posterior orifice benefits grain." Wang Haogu stated: "Water metabolism is governed by the Spleen, Lung, and Kidney meridians. Water pathology can involve parts of the five zang, six fu, and twelve meridians, affecting the head and face above, limbs in the middle, waist and legs below, skin externally, muscles deeply, and bones internally. Pulse diagnoses vary between cun and chi positions and floating and sinking qualities. One should not lightly use purgative medicines; one must know which meridian and zang-fu are affected before prescribing. Note: Edema may result from phlegm encasing food stagnation and blood stasis, causing clear yang to fail to ascend and turbid yin to fail to descend, constituting an excess syndrome. It may also result from mutual generation of damp-heat and obstruction of channels, also an excess syndrome. Or it may result from dry-heat impact and constipation, also an excess syndrome. Conversely, it may result from taking cold-cooling herbs that damage digestion and cause deficiency of Middle Qi, or from exhaustion of healthy qi after severe illness, or from inability of the Spleen to control water due to urinary retention and chaotic water flow, constituting a deficiency syndrome. These should be treated differently. However, the root cause often lies in deficiency of Middle Qi. Zhu Danxi said: 'In treating water diseases, priority should be given to strengthening the Spleen. When the Spleen is solid and Qi moves, water flows naturally.' Ren Shen (Ginseng Radix) and Fu Ling (Poria) should be used as sovereign drugs, modified according to accompanying syndromes. If only diuretics are used, it often leads to untreatable conditions." It also treats Jiajian masses and hernias, retained fluids and old food, and epilepsy caused by phlegm confusing the mind. It is contraindicated in deficiency cases.
The bark is reddish, the flesh is white, and the root resembles a string of pearls. Those that are heavy and solid are superior. For use, wrap in flour and bake until cooked (or soak in Gancao [Licorice Root] and Qicai juice for three days; when the liquid turns black like ink and then clears, wrap in flour and bake again). Gouti (Melon Stalk) serves as an assistant. It is incompatible with Yuanzhi (Polygalae Radix). It is chemically antagonistic to Gancao (Glycyrrhizae Radix et Rhizoma) (Zhang Zhongjing used it together with Gancao to treat retained fluid under the heart, utilizing their antagonistic interaction to achieve therapeutic effect. In some cases treating edema and sores, applying Gansui powder to the swollen area while administering concentrated Gancao decoction orally causes immediate reduction of swelling, demonstrating such strong reciprocal induction between the two herbs).