经曰∶“二阳结（足阳明胃，手阳明大肠），谓之消。”同一结也，而气分、血分判焉（病在气分则渴，
病在血分则不渴。消渴以渴为主而判气血，血分亦有渴者）。气分结者，病发于阳；血分结者，病发于阴。
二症相反，如同冰炭。其发于阳也，阳明被火煎熬，时引冷水自救，脉浮洪而数；其发于阴也，阳明无水涵濡，
时引热水自救，脉沉弱而迟。发于阳者，石膏、黄连，可以折狂妄之火（石膏、知母、炙草、黄连、粳米），
人所共知；发于阴者，其理最为微妙，非三折其肱，殊难领会。人之灌溉一身，全赖两肾中之水火（津液发源
于华池，涌于廉泉，为甘露、为琼浆，以养百骸。华池，两肾中先天之祖窍，水火朕兆处。廉泉，舌下二穴
名），犹之甑乘于釜，釜中水足，釜底火盛，而甑自水气交流，倘水涸火熄，而甑反干枯缝裂，血分之渴，作
如是观。当此舌黑肠枯之时，非重用熟地，不足以滋其水；非重用附桂，不足以益其火（八味汤∶肉桂、附子
、熟地、山药、枣皮、泽
泻、丹皮、云苓），火炽水腾，而渴自止。余尝治是症，发于阳者，十居二三，发于阴者，十居七八，用桂附
多至数斤而愈者。彼本草所注，无非治气分之品，而治血分之药性，不注于本草，方实始于仲景，至喻嘉言
而昌明其说。上消如是，中下消可类推矣（胃热多食善饥为中消，肾热渴而小便有膏为下消。治法仍分气血。
下消小便甜者难治，水生于甘而死于咸，小便本咸而反甘，是脾气下陷肾中，土克水而生气泄也）。昔汉武帝
患是症，仲景进桂附八味汤，服之而愈，因赐相如服之不效。或曰，相如之渴，发于气分。或曰，相如为房劳
所伤，非草木之精华所能疗。武帝不赐方而赐以金茎露一杯，（李商隐诗∶“侍臣最有相如渴，不赐金茎露一
杯”），庶几愈焉，未可知也。
The *Classic of Medicine* (Huangdi Neijing) states: "When the two Yang meridians are constrained, it is called Xiao [Wasting and Thirsting]." Although both involve constraint, the pathology differs between the Qi level and the Blood level (Pathology at the Qi level manifests as thirst, while pathology at the Blood level typically does not. Since Xiao syndrome is primarily characterized by thirst, this criterion distinguishes Qi from Blood; however, thirst can also occur in Blood-level pathology). Constraint at the Qi level originates from Yang; constraint at the Blood level originates from Yin. These two presentations are opposite, akin to ice and charcoal.
In cases originating from Yang, the Stomach (Yangming) is scorched by fire, leading the patient to crave cold water for self-soothing; the pulse is floating, surging, and rapid. In cases originating from Yin, the Stomach lacks yin fluids to nourish it, leading the patient to crave hot water for self-soothing; the pulse is deep, weak, and slow. For those originating from Yang, using Shigao (Gypsum Fibrosum) and Huanglian (Coptidis Rhizoma) to subdue reckless fire (as seen in formulas containing Gypsum Fibrosum, Anemarrhenae Rhizoma, Glycyrrhizae Radix et Rhizoma Preparata, Coptidis Rhizoma, and Oryzae Fructus) is well known. However, for those originating from Yin, the principle is most subtle and difficult to comprehend without profound medical expertise.
The body's irrigation relies entirely on the balance of Water and Fire within the two Kidneys (Jinye [Body Fluids] originate from Huachi, surge forth from Lianquan, transforming into sweet dew and fine nectar to nourish the bones and viscera. Huachi refers to the primordial aperture within the two Kidneys, where the signs of Water and Fire emerge. Lianquan refers to the acupoints located under the tongue). This is like a steamer placed over a pot: if the pot has sufficient water and the fire beneath is strong, steam naturally circulates. If the water dries up and the fire extinguishes, the steamer becomes dry and cracks. The thirst associated with Blood-level pathology should be understood in this manner. When the tongue appears black and the intestines are dried out, only heavy doses of Shudi (Rehmanniae Radix Preparata) can nourish the Water; only heavy doses of Rougui (Cinnamomi Cortex) and Fuzi (Aconiti Lateralis Radix Preparata) can tonify the Fire (Ba Wei Wan [Eight-Ingredient Pill]: Cinnamomi Cortex, Aconiti Lateralis Radix Preparata, Rehmanniae Radix Preparata, Dioscoreae Rhizoma, Corni Fructus, Alismatis Rhizoma, Moutan Cortex, Poria). When Fire blazes and Water rises, thirst ceases naturally.
I have treated such cases; those originating from Yang account for two or three out of ten, while those originating from Yin account for seven or eight out of ten. I have cured patients by using large quantities (several jin) of Rougui and Fuzi. Materia Medica texts mainly record herbs for treating Qi-level conditions, but rarely detail the properties of herbs for treating Blood-level conditions. This therapeutic approach actually originated with Zhang Zhongjing and was elucidated by Yu Jiayan. The same logic applies to Shangxiao [Upper Wasting-Thirst]; Zhongxiao [Middle Wasting-Thirst] and Xiaxiao [Lower Wasting-Thirst] can be inferred similarly (Zhongxiao is characterized by stomach heat, excessive eating, and easy hunger; Xiaxiao is characterized by kidney heat, thirst, and fatty urine. Treatment still distinguishes between Qi and Blood levels. Xiaxiao with sweet urine is difficult to treat because water is born from sweetness and dies from saltiness; urine should naturally be salty, but if it becomes sweet, it indicates Spleen Qi sinking into the Kidney, where Earth overcomes Water, causing the leakage of vital Qi).
In ancient times, Emperor Wu of Han suffered from this condition. Zhang Zhongjing prescribed Ba Wei Wan (Eight-Ingredient Pill with Cinnamon and Prepared Aconite), which cured him. Consequently, the emperor granted Sima Xiangru the same prescription, but it was ineffective. Some argue that Sima Xiangru’s thirst originated from the Qi level. Others suggest that Sima Xiangru was injured by sexual exhaustion, which cannot be cured by herbal essences alone. Instead of granting a medicinal formula, Emperor Wu gave Sima Xiangru a cup of Dew Collected from the Golden Stem (Li Shangyin wrote: "Among the attendants, Sima Xiangru had the greatest thirst, yet he was not granted a cup of Dew from the Golden Stem"). Perhaps this would have healed him, though this remains uncertain.