热者，少阴君火之所化也。在天为热，在地为火，在人为心。少阴以君火主令，手少阴心火也，足少
阴肾水也，水火异气，而以君火统之。缘火位于上，而生于下，坎中之阳，火之根也。坎阳升则上交离位
而化火，火升于水，是以癸水化气于丁火。水化而为火，则寒从热化，故少阴之气，水火并统，而独
以君火名也。君火虽降于手，而实升于足。阳盛则手少阴主令于上，而癸水亦成温泉。阴盛则足
少阴司气于下，而丁火遂为寒灰。以丁火虽司气化，而制胜之权，终在癸水，所恃者，生
土以镇之。但土虽克水，而百病之作，率由土湿，湿则不能克水，而反被水侮。土能克水者，惟伤寒阳
明承气一证，其余则寒水侮土者，十九不止。土溃则火败，故少阴一病，必寒水泛滥，而火土俱负
，其势然也。至于上热者，此相火之逆也。火中有液，癸水之根。
相火上逆，灾及宫城。心液消亡，是以热作。凡少阴病热，乃受累于相火，实非心家之过。而方其上热，
必有下寒，以水火分离而不交也。见心家之热，当顾及肾家之寒。盖水火本交，彼此相交，则为一气，
不交则离析分崩，逆为冰炭。究之火不胜水，则上热不敌下寒之剧，不问可知也。血根于心，而藏于肝，
气根于肾，而藏于肺，心火上热则清心家之血，肾水下寒则暖肾家之气。故补肝之血，则宜温；补心之血，
则宜清；补肺之气，则宜凉；补肾之气，则宜暖；此定法也。
热，是少阴君火所化生的。在天为热，在地为火，在人为心。少阴以君火（主宰之火）主令，手少阴心属火，足少阴肾属水，水火性质不同，但由君火统摄。因为火位于上，而根生于下，坎卦中的阳爻，就是火的根本。坎中阳气上升则上交于离位而化为火，火升于水中，所以癸水（肾阴/真水）化气于丁火（心阴/君火）。水转化为火，则寒从热而化，所以少阴之气，水火并统，却唯独以君火命名。君火虽然下行于手经，但实际上根源于足经。阳气盛时，手少阴心火主令于上，而癸水也变成温泉；阴气盛时，足少阴肾水司气于下，而丁火便成为寒灰。由于丁火虽然主管气化，但制胜的权力，终究在于癸水，所依赖的是生土来镇制它。但是土虽然克水，然而百病的发生，大多由于土湿，湿则不能克水，反而被水反侮。土能克水的，只有伤寒阳明病承气汤证这一种情况，其余则是寒水反侮土的，十有八九不止。土溃败则火衰败，所以少阴一经发病，必定是寒水泛滥，而火与土都受损，这是势所必然的。至于上部的热，这是相火（寄居于肝肾之火）上逆所致。火中有液，是癸水的根本。相火上逆，灾害波及宫城（心脏）。心液消亡，因此产生热。凡是少阴病出现热象，都是受相火牵连，实在不是心脏本身的过错。而在上部有热的同时，必定下部有寒，这是因为水火分离而不相交。见到心脏的热，应当顾及肾脏的寒。因为水火本应相交，彼此相交，就合为一气，不相交就会离散崩解，逆转为冰炭对立。究其根本，火不胜水，所以上部的热敌不过下部寒的剧烈程度，是不问自明的。血根于心，而藏于肝；气根于肾，而藏于肺。心火导致上热，则需清心家之血；肾水导致下寒，则需暖肾家之气。所以补肝之血，宜用温法；补心之血，宜用清法；补肺之气，宜用凉法；补肾之气，宜用暖法；这是固定的法则。
Heat is the transformation of Shaoyin Junhuo (Monarch Fire, the ruling fire). In Heaven it manifests as heat, in Earth as fire, and in Humanity as the Heart. Shaoyin governs by means of Junhuo; the Hand-Shaoyin channel belongs to the Heart-Fire, while the Foot-Shaoyin channel belongs to Kidney-Water. Although Water and Fire have different natures, they are unified under the Monarch Fire. This is because Fire resides above but originates below; the Yang within Kan (☵) is the root of Fire. When the Yang of Kan ascends, it joins with Li (☲) above to transform into Fire; as Fire rises within Water, Gui Water (Kidney Yin/True Water) transforms its Qi through Ding Fire (Heart Yin/Monarch Fire). When Water transforms into Fire, Cold transforms from Heat. Thus, the Qi of Shaoyin unifies both Water and Fire, yet is named solely after Junhuo. Although Junhuo descends via the Hand channels, its root actually ascends via the Foot channels. When Yang is abundant, Hand-Shaoyin Heart-Fire governs above, and Gui Water becomes like hot springs. When Yin is abundant, Foot-Shaoyin Kidney-Water governs below, and Ding Fire becomes cold ash. Although Ding Fire manages Qi transformation, the power of control ultimately lies with Gui Water, which relies on generating Earth to suppress it. However, although Earth controls Water, the onset of most diseases stems from Dampness in Earth. When Damp, Earth cannot control Water but is instead insulted by Water. The only case where Earth effectively controls Water is in the Yangming Chengqi Decoction syndrome of Cold Damage; in other cases, Cold Water insulting Earth accounts for more than ninety percent. If Earth collapses, Fire fails. Therefore, in any Shaoyin disease, Cold Water inevitably floods, causing both Fire and Earth to suffer defeat; this is the inevitable trend. As for Heat in the upper part, this is due to the rebellion of Xianghuo (Ministerial Fire). Within Fire there is Fluid, which is the root of Gui Water. When Ministerial Fire rebels upward, disaster reaches the Palace City (the Heart). The destruction of Heart Fluid results in Heat. Whenever Shaoyin disease presents with Heat, it is affected by Ministerial Fire, not truly an error of the Heart itself. Wherever there is Heat above, there must be Cold below, because Water and Fire are separated and do not interact. When observing Heat in the Heart, one must consider Cold in the Kidneys. Fundamentally, Water and Fire should interact; when they interact, they become one Qi. When they do not interact, they separate and collapse, turning into opposing Ice and Charcoal. Ultimately, Fire cannot overcome Water; thus, the Heat above cannot match the severity of the Cold below, which is self-evident. Blood has its root in the Heart but is stored in the Liver; Qi has its root in the Kidney but is stored in the Lung. If Heart-Fire causes Heat above, one should clear the Blood of the Heart. If Kidney-Water causes Cold below, one should warm the Qi of the Kidney. Therefore, tonifying Liver Blood requires a Warm method; tonifying Heart Blood requires a Clear method; tonifying Lung Qi requires a Cool method; tonifying Kidney Qi requires a Warm-Nourishing method. These are fixed principles.