黄帝问曰。余闻揆度奇恒所指不同。岐伯对曰。揆度者。度病之浅深也。奇恒者。言奇病也。夫恒之为道。谓胃气
五脏。各得其所。上顺天时。内调营卫。故神转不回。转、流动也。回、逆曲也。回则不转。乃失其机。于是脏腑曲逆。
克制凌犯。神机之运用失矣。失则不循恒道。有非恒道所可得而揆度也。于是岐伯又设奇恒一门。以度奇病。其文本六
十首。书阙简脱。今可论者十之二耳。如五脏别论。奇病论。大奇论。脉解篇。气厥论。腹中论。逆调论。病能论诸篇。
俱从运气脏腑经络而外。拈其病之厥逆错杂。所谓回则不转。乃失其机者也。此开后世内伤杂证之大经大法也。乃为纲
领。其说曰行奇恒之法。以太阴始。夫手太阴为元气之主。足太阴为六经之主。奇病之作。必变于元气神机之失。不失
必占于元气。故虽奇病之千变万化。而一以太阴为准。此又治奇恒之大宗也。乃内经又有拈脏腑本来之奇恒者。此原其
所以奇之故也。经曰、脑髓骨脉胆女子胞。此六者地气之所生也。皆藏于阴。而象于地。故藏而不泻。名曰奇恒之府。
又曰魄门。为五脏使。与前为七。而唯胆属少阳。特曰中精之府。此七者之有病。其受病不与脏腑之主时者同。是脏腑
之一异也。有出于脏腑体要之奇恒者。如腹中论。诸病外不涉于形身。内不关于脏腑。病在宫城空廓之中。或气或血。
或风或热。以至女子妊娠。皆在空腹之中。虽胆中三焦督任五脏之散络悉在。而其病止属肝脾。以肝脾为腹中之主故也。
此体要之一异也。有脏腑交加之奇恒者。如气厥论。寒热之相移。不论顺传逆传。而以气之所之相并为病。逆调论。寒
热阴阳之所相胜而为病。调经论。表里上下阴阳气血之相并。互相胜负而为病。夫阴阳气血寒热之相并相胜。不系四时。
不缘感召。要皆积渐之所致。迨病至而相胜相并。此实内伤不足之所由。所以异于恒者也。是病源之一异也。又有脏腑
颇僻之奇恒者。如大奇论。脏腑脉各见颇僻以成病。有肿满偏枯痫螈。风水肠 之证。而皆非脏腑主时之恒病。则厥逆
之由来既久。必须揆度脉气病由。而治之有别。是又疾病之一异也。又有六气错出。互为体用之奇恒者。如脉解篇。太
阳主寅。少阳主戌。厥阴主辰。太阴主子。又云四月五月。人气在头。八月九月。人气在心。原其然者。人身恒常之气。
由下而上。由上而下。故正月人气在肝。而三阳初出于寅。故太阳主寅。厥阴木火主气。故厥阴为辰。九月人气在心者。
以气由肺而下始。次至心少阳。为心表为相火。故亦次心而主九月戌。太阴为阴中之至阴。十一月阴尽而纯坤见。故太
阴主子。此又与本经三月四月人气在脾者不同。凡阴阳乘除。每各一道。并行不悖。俱非恒道。而要不可背之为道。是
又阴阳之一异也。又有八奇经见病之奇恒者。如刺腰篇。十二经皆有腰。盖以带脉之为诸经钤束故也。若阴阳两跷。出
阳入阴。出阴入阳。而机关于目。阴阳二维。别为部于阴阳之会。而主指之内外。冲督任脉一源而三歧。而各统阴阳之
海。所得之病。既非十二经之恒常。而十二经每与之俱病。又奇道之一异也。是故人之一身。其为阴阳脏腑五行恒转。
而神机攸序。乃既有前七者。脏腑之孤阴。不伦于恒等。有部位之关要。不涉于众流。又有病源之乘。痼疾之积。阴阳
错出之异。奇经为病之别。苟非揆度执之恒理。而不求其所由然。安能使神机之转而不回耶。
黄帝问道：我听说“揆度”与“奇恒”所指的含义不同。岐伯回答说：“揆度”，是衡量病情的深浅程度；“奇恒”，是指谈论奇特的疾病。所谓“恒道”，是指胃气滋养五脏，使各脏腑功能安适有序，上顺应天时，内调和营卫（运行于脉外的卫气和运行于脉内的营气），因此神机运转不息。“转”，指流动变化；“回”，指逆乱弯曲。如果逆乱则不能流转，这就失去了生机。于是脏腑功能逆乱，相互克制侵犯，神机的运用也就丧失了。一旦丧失，就不遵循常道，有了非正常规律所能衡量的情况。因此岐伯又设立“奇恒”这一门类，用来衡量奇特疾病。原文共有六十篇，但书籍残缺、竹简脱落，现在可以讨论的只有十分之二罢了。例如《五脏别论》、《奇病论》、《大奇论》、《脉解篇》、《气厥论》、《腹中论》、《逆调论》、《病能论》等篇章，都不局限于运气、脏腑、经络的理论，而是选取那些病情厥逆错杂的情况，也就是所说的“逆乱则不能流转，从而失去生机”。这是开启后世内伤杂证诊治的大法纲领。其说法是：施行奇恒之法，从太阴开始。手太阴肺经是元气的主宰，足太阴脾经是六经的主宰。奇特疾病的发作，必然改变元气和神机的正常运行，如果不失常，必定体现在元气上。所以虽然奇病千变万化，但都以太阴为准绳。这又是治疗奇恒病的根本大法。
此外，《内经》还有从脏腑本来属性角度论述奇恒的内容，这是探究它们之所以“奇”的原因。经文说：脑、髓、骨、脉、胆、女子胞（子宫），这六个器官是由地气所生，都藏于阴，象征大地，所以只贮藏精气而不泻出，称为“奇恒之府”（形态似腑而功能似脏的器官）。又说：魄门（肛门）是五脏的使者，与前文合为七个，唯独胆属于少阳，特别称为“中精之府”（储存精汁的腑）。这七个器官患病时，其受病规律与脏腑主时的常规不同，这是脏腑属性上的一个差异。
有出于脏腑体要方面的奇恒，如《腹中论》所述：各种疾病外表不波及形体身躯，内部不关联脏腑实质，病位在宫城空廓之中，或是气、血、风、热所致，以至女子的妊娠，都在空腹之中发生。虽然胆、三焦、督脉、任脉以及五脏的散络都存在于腹腔，但其病变主要归属于肝脾，因为肝脾是腹腔的主宰，这是体要方面的一个差异。
有脏腑交加之奇恒，如《气厥论》所述：寒热之气的相互转移，不论顺传还是逆传，而是以气机汇聚之处形成病症。《逆调论》所述：寒热阴阳相互胜负而形成病症。《调经论》所述：表里上下、阴阳气血相互汇聚，互相胜负而形成病症。阴阳气血寒热的相互汇聚和胜负，不取决于四季时令，也不源于外感邪气，都是逐渐积累所致。等到疾病发作而相胜相并，这实际上是内伤不足所造成的，所以不同于常道，这是病源方面的一个差异。
又有脏腑偏颇的奇恒，如《大奇论》所述：脏腑脉象各自出现偏颇而形成疾病，有肿胀、满闷、偏枯（半身不遂）、痫证、抽搐、风水、肠澼（痢疾）等证候，而这些都不是脏腑主时的常规疾病。那么厥逆的由来已经很久，必须衡量脉气和病因，治疗方法也就有所不同，这是疾病表现方面的一个差异。
又有六气错出、互为体用的奇恒，如《脉解篇》所述：太阳经主管寅时，少阳经主管戌时，厥阴经主管辰时，太阴经主管子时。又说：四月五月，人气在头部；八月九月，人气在心部。探究其原因，人身恒常之气，由下而上，由上而下。所以正月人气在肝，而三阳初出于寅时，故太阳经主管寅时。厥阴木火主气，故厥阴经主管辰时。九月人气在心部的原因，是因为气由肺下行开始，其次到达心、少阳，心为少阳之表，少阳为相火，所以也次于心而主管九月戌时。太阴是阴中之至阴，十一月阴气尽而纯坤显现，故太阴经主管子时。这又与本经三月四月人气在脾的情况不同。凡是阴阳消长，各有其道，并行不悖，都不属于恒常之道，但要不可违背它作为准则，这是阴阳运行方面的一个差异。
又有八条奇经见病的奇恒，如《刺腰篇》所述：十二经脉都有腰部病变，大概是因为带脉约束诸经的缘故。若阴阳两跷脉，出阳入阴，出阴入阳，机关在目；阴阳二维脉，分别位于阴阳交会之处，主管手指内外；冲脉、督脉、任脉同源而三歧，各自统摄阴阳之海。所得到的疾病，既不是十二经脉的常规病变，而十二经脉常常与之并发，这又是奇经病变的一个差异。
因此，人的一身，其阴阳、脏腑、五行恒常运转，神机有序。既然有了前七种情况：脏腑孤阴不与常伦相同，部位关要不涉于众流，病源乘袭，痼疾积聚，阴阳错出的差异，奇经为病的区别，如果不是衡量并执守常理，而不探求其所以然的原因，怎么能使神机运转而不逆乱呢？
Yellow Emperor asked, saying: I have heard that the terms "Kui Du" (Measuring and Estimating) and "Qi Heng" (Abnormal and Constant) refer to different concepts. Qi Bo replied, saying: "Kui Du" refers to measuring the depth and superficiality of a disease. "Qi Heng" refers to discussing abnormal or strange diseases. The so-called "Heng Dao" (Constant Way) implies that Stomach Qi nourishes the Five Zang Organs, allowing each organ to function in its proper place, harmonizing with Heaven's timing above and regulating Ying and Wei Qi (Nutritive and Defensive Qi) within. Thus, the Shen Ji (Spirit Mechanism) turns without stopping. "Zhuan" means flowing and changing; "Hui" means reversing and twisting. If it reverses, it cannot flow, thereby losing its vital opportunity. Consequently, the functions of the Zang-Fu organs become twisted and reversed, leading to mutual restriction and infringement, and the operation of the Shen Ji is lost. Once lost, it no longer follows the constant way, resulting in conditions that cannot be measured by normal standards. Therefore, Qi Bo established the category of "Qi Heng" to measure these abnormal diseases. The original text consisted of sixty chapters, but due to missing books and lost bamboo slips, only about two-tenths remain discussable today. For instance, chapters such as *Lun Wu Zang Bie* (Discourse on the Distinction of the Five Zang Organs), *Qi Bing Lun* (Discourse on Abnormal Diseases), *Da Qi Lun* (Great Discourse on Abnormalities), *Mai Jie Pian* (Explanation of Pulse Patterns), *Qi Jue Lun* (Discourse on Qi Reversal), *Fu Zhong Lun* (Discourse on the Abdomen), *Ni Diao Lun* (Discourse on Irregular Regulation), and *Bing Neng Lun* (Discourse on Disease Capabilities), do not merely rely on theories of Luck (Yun Qi), Zang-Fu, or Meridians. Instead, they highlight cases of disease reversal and complexity, described as "reversal leads to stagnation, thus losing the vital opportunity." This opened the great principles and methods for treating internal injury and miscellaneous syndromes in later generations, serving as a guideline. The principle states: To practice the method of Qi Heng, one should begin with Tai Yin. Hand Tai Yin Lung Meridian is the master of Yuan Qi (Original Qi), and Foot Tai Yin Spleen Meridian is the master of the Six Meridians. The onset of abnormal diseases must alter the normal operation of Yuan Qi and Shen Ji; if not altered, it must manifest in Yuan Qi. Therefore, although abnormal diseases are myriad and changing, they all take Tai Yin as the standard. This is another major principle for treating Qi Heng conditions.
Furthermore, the *Nei Jing* discusses Qi Heng from the perspective of the inherent nature of Zang-Fu organs, exploring the reasons why they are considered "abnormal." The Classic states: Brain, Marrow, Bones, Vessels, Gallbladder, and Uterus (Female Womb) are generated by Earth Qi. They all store Yin and resemble the Earth; thus, they store essence without excreting, and are named the "Qi Heng Fu" (Extraordinary Fu Organs). It also states: The Po Men (Anus) serves as the envoy of the Five Zang Organs, making seven in total with the previous six. However, only the Gallbladder belongs to Shaoyang and is specifically called the "Zhong Jing Zhi Fu" (Organ storing pure fluid). When these seven organs suffer disease, their pathology differs from the regular timing of Zang-Fu diseases; this is one difference in Zang-Fu attributes.
There are abnormalities arising from the essential aspects of Zang-Fu, as discussed in *Fu Zhong Lun*: Various diseases do not affect the exterior body shape nor involve the interior Zang-Fu substance directly; the pathology lies in the empty spaces of the abdominal cavity. Whether caused by Qi, Blood, Wind, or Heat, or even pregnancy in women, these occur within the abdominal void. Although the dispersing collaterals of the Gallbladder, Sanjiao, Du Mai, Ren Mai, and Five Zang Organs are present there, the pathology primarily belongs to the Liver and Spleen because they are the masters of the abdomen. This is one difference in essential aspects.
There are abnormalities involving the intersection of Zang-Fu, as seen in *Qi Jue Lun*: The transfer of Cold and Heat does not follow strictly sequential or reverse transmission but forms disease where Qi gathers. In *Ni Diao Lun*, disease arises from the mutual victory and defeat of Cold, Heat, Yin, and Yang. In *Tiao Jing Lun*, disease results from the convergence of Exterior/Interior, Upper/Lower, Yin/Yang, Qi/Blood, leading to mutual dominance. The convergence and conflict of Yin, Yang, Qi, Blood, Cold, and Heat are not determined by the four seasons nor caused by external pathogens, but are the result of gradual accumulation. When the disease manifests and these forces clash, it is actually due to internal injury and deficiency, differing from the constant way. This is one difference in disease origin.
There are abnormalities characterized by Zang-Fu deviation, as described in *Da Qi Lun*: Zang-Fu pulse patterns show deviations leading to disease, presenting symptoms such as swelling, fullness, hemiplegia, epilepsy, convulsions, Feng Shui (Wind Water edema), and Chang Pi (Dysentery). These are not constant diseases associated with the ruling Zang-Fu of specific times. Since the cause of reversal has been long-standing, one must measure the pulse Qi and disease etiology, and treatment will differ. This is one difference in disease presentation.
There are abnormalities involving the交错 (interlacing) of the Six Qi acting as substance and function, as illustrated in *Mai Jie Pian*: The Tai Yang meridian governs the Yin hour, Shaoyang governs the Xu hour, Jueyin governs the Chen hour, and Taiyin governs the Zi hour. It also states: In the fourth and fifth months, Human Qi is in the head; in the eighth and ninth months, Human Qi is in the heart. Investigating the reason, the constant Qi of the human body moves from below to above and from above to below. Thus, in the first month, Human Qi is in the Liver, and since the Three Yang emerge initially at Yin, Tai Yang governs Yin. Jueyin Wood and Fire govern Qi, so Jueyin governs Chen. In the ninth month, Human Qi is in the Heart because Qi begins descending from the Lungs, then reaches the Heart and Shaoyang. The Heart is the exterior of Shaoyang, and Shaoyang is Ministerial Fire, so it also governs the ninth month Xu hour following the Heart. Taiyin is the Ultimate Yin within Yin. In the eleventh month, Yin energy ends and Pure Kun appears, so Taiyin governs Zi. This differs from the statement in the same Classic that Human Qi is in the Spleen during the third and fourth months. Whenever Yin and Yang wax and wane, each follows its own path, running parallel without contradiction, yet none belong to the constant way, though one must not deviate from them as principles. This is one difference in Yin-Yang dynamics.
There are abnormalities manifested by the Eight Extraordinary Vessels, as mentioned in *Ci Yao Pian*: All twelve meridians can have waist-related issues, largely because the Dai Mai (Girdle Vessel) binds the other meridians. The Yin and Yang Qiao Mai enter Yang and exit Yin, and vice versa, with their mechanism centered in the eyes. The Yin and Yang Wei Mai are located separately at the intersections of Yin and Yang, governing the inner and outer aspects of the fingers. The Chong, Du, and Ren Mai share a source but branch into three, each commanding the seas of Yin and Yang. The diseases obtained are neither constant diseases of the twelve regular meridians, yet the twelve meridians often suffer alongside them. This is another difference in the pathways of the extraordinary vessels.
Therefore, in the human body, Yin-Yang, Zang-Fu, and Five Elements turn constantly, and the Shen Ji operates in order. Given the aforementioned seven differences—Zang-Fu isolated Yin not conforming to norms, critical locations not involved with common flows, disease origins being invaded, chronic diseases accumulating, differences in Yin-Yang interlacing, and distinct diseases of the extraordinary vessels—if one does not measure and adhere to constant principles while seeking their underlying causes, how can one ensure the Shen Ji turns without reversing?