此在口诀。阴真人云∶若欲长生，当服内气。《素问》云∶圣人传精神，服天气而通神明。天
气者，内气也。《阴符经》云∶天生天煞，食元和之气。天不能煞，地不能埋，名之曰真人。故修
行之士，饥食元和之气，渴饮华池之水。老子所谓实其腹者，此也。若未绝粒人，欲服气，当须少
食，务要腹中旷然虚静。然亦无早晚，腹空则咽之。然而所以要口诀者，服气须分内外、辨清浊、别
咽喉。不分内外，则吸邪气；不辨清浊，则无分两；不别咽喉，则不入胃脘。
此在口诀。人之得体，始于北极元泉之下。元泉者，真一也。自丹田上朝舌下二窍，谓之神水华
池，咀嚼至浓。养生家名曰炼精合虚。鼓漱搅成大药，其数一周天，赤龙不能胜载，方为铅汞重宝。
内想神宫，微微出气，作意咽之，直令喉中作声，下入丹田中，凝结如鸡子洁白状。紫河车歌曰∶
左为日兮右为月，两半同升合为一。出彼玉池入金室，大如
弹丸黄如桔。中有佳味甘如蜜，子若得之慎勿失。审能修之仙道毕。《内景经》亦云∶舌下玄膺生
死岸。又曰∶玉池清水灌灵根，审能修之命长存。《赤城长生记》∶人身上之津液，非漱咽则无以
灌溉于五脏，发其光泽也。
太白真人云∶五行颠倒术，龙从火里出。五行不顺行，虎向水中生。又曰∶欲知颠倒术，相克
乃相生。又曰∶欲知颠倒由离坎，须识浮沉定主宾。《草堂歌》曰∶若欲学长生，先须 五行。
五行不颠倒，还丹不解成。会得五行颠倒，方知利中有害，害却成利。珞 子云∶每见凶中有吉，
吉乃先凶。《阴符经》所谓天有五贼，见之者昌。且以天地万物观之，无有不颠倒者。然须识真五行，
方解颠倒术。曹真人云∶五行处处有，岂是真人惜。欲识五行真，一水还一石。郑真人云∶一阴
一阳之谓道，一水一石之谓丹。又歌曰∶为得铅中金，兼得石中水。盖水中出金，石中出液。
这关键在于口诀。阴真人说：如果想要长生，应当服用内气。《素问》说：圣人保全精神，顺应天气而通达神明。天气，就是内气。《阴符经》说：天生成万物也肃杀万物，食用元和之气。天不能肃杀它，地不能埋葬它，这样的称为真人。所以修行之人，饿了吃元和之气，渴了喝华池之水。老子所说的“充实他的腹部”，指的就是这个。如果还没有断绝谷物的人，想要服气，应当减少饮食，务必使腹中空旷虚静。然而也没有固定的早晚时间，肚子空了就吞咽。然而之所以强调口诀的原因，是因为服气必须区分内外、辨别清浊、分别咽喉。不区分内外，就会吸入邪气；不辨别清浊，就没有分量标准；不分别咽喉，气就不能进入胃脘。
这关键在于口诀。人的得道体悟，始于北极元泉之下。元泉，就是真一。从丹田向上到达舌下的两个窍穴，称为神水华池，咀嚼至浓稠。养生家称之为炼精合虚。鼓漱搅动成为大药，运行一周天，赤龙（舌头）不能承受其重，这才算是铅汞重宝。内心想象神宫，微微呼气，有意吞咽，直令喉中发出声音，下行进入丹田中，凝结如鸡蛋洁白状。紫河车歌说：左边是日右边是月，两半同升合为一。出自玉池进入金室，大如弹丸黄如桔。其中有甘甜味道甘如蜜，你若得到它务必不要丢失。若能仔细修炼则仙道可成。《内景经》也说：舌下玄膺处有生死之岸。又说：玉池清水灌溉灵根，若能仔细修炼则寿命长存。《赤城长生记》说：人身上的津液，如果不经过漱咽就无法灌溉五脏，使其发出光泽。
太白真人说：五行颠倒术，龙从火里出。五行不顺行，虎向水中生。又说：想要知道颠倒术，相克即是相生。又说：想要知道颠倒的由来在于离坎，必须认识浮沉以定主宾。《草堂歌》说：如果想要学习长生，必须先懂五行。五行不颠倒，还丹就不能结成。懂得五行颠倒，才知道利中有害，害却能转化为利。珞子说：常常见到凶中有吉，吉往往是先凶。《阴符经》所谓的天有五贼，见到它的人昌盛。且以天地万物来看，没有不颠倒的。然而必须认识真正的五行，才能理解颠倒术。曹真人说：五行处处都有，难道是真人吝惜吗？想要认识五行的真谛，就是一水和一石。郑真人说：一阴一阳叫做道，一水一石叫做丹。又歌说：为了得到铅中的金，兼得石中的水。大概水中出金，石中出液。
This lies in the secret formula. Zhenren Yin (Perfected One Yin) said: If you wish for longevity, you should ingest internal Qi (vital energy). The *Suwen* (Basic Questions) states: The sage preserves spirit and mind, conforms to Heaven's Qi, and connects with divine illumination. "Heaven's Qi" refers to internal Qi. The *Yinfu Jing* (Book of the Hidden Talisman) states: Heaven generates and destroys; one consumes the Qi of Yuanhe (Primordial Harmony). Neither Heaven can destroy it nor Earth bury it; such a person is called a Zhenren (Perfected One). Therefore, practitioners of cultivation eat the Qi of Yuanhe when hungry and drink the water of Huachi (Splendid Pool) when thirsty. What Laozi referred to as "filling his abdomen" points to this. For those who have not yet ceased eating grains, if they wish to practice Qi ingestion, they must reduce food intake, ensuring the abdomen remains empty, vast, and tranquil. There is no fixed time for morning or evening; one swallows whenever the stomach is empty. However, the reason the secret formula is emphasized is that Qi ingestion requires distinguishing between internal and external, differentiating clear from turbid, and identifying the throat. Failing to distinguish internal and external leads to inhaling pathogenic Qi; failing to differentiate clear and turbid results in lacking proper dosage; failing to identify the throat prevents the Qi from entering the stomach.
This lies in the secret formula. Human attainment begins below the Primeval Spring of the North Pole. The Primeval Spring is the True Unity (Zhenyi). From the Dantian (Elixir Field), it ascends to two apertures under the tongue, known as Shenshui (Divine Water) and Huachi (Splendid Pool), chewed until thick. Health cultivators call this "refining Jing (essence) to merge with emptiness." By rinsing and stirring into a great medicine, completing one cycle of the Microcosmic Orbit, the Red Dragon (tongue) cannot bear its weight, marking it as the precious treasure of Lead and Mercury. Internally visualizing the Divine Palace, exhale slightly, intentionally swallow, causing a sound in the throat, directing it down into the Dantian, where it condenses like the white yolk of an egg. The Song of Ziheche (Purple River Cart) says: Left is Sun, right is Moon; both halves rise together to become one. Exiting the Jade Pool entering the Golden Chamber, large as a pellet, yellow as an orange. Within lies a fine taste, sweet as honey. If you obtain it, guard it carefully. Careful cultivation completes the Dao of Immortality. The *Neijing Jing* (Classic of Internal Scenery) also states: At Xueying (Dark Diaphragm) under the tongue lies the shore of life and death. It further states: Clear water from the Jade Pool irrigates the Spiritual Root; careful cultivation ensures long life. The *Chicheng Changsheng Ji* (Record of Longevity in Chicheng) states: The fluids in the human body, unless rinsed and swallowed, cannot irrigate the Five Viscera (Zang Organs) and cause them to shine.
Taibai Zhenren (Perfected One Taibai) said: In the art of reversing the Five Elements (Wuxing), the Dragon emerges from Fire. When the Five Elements do not proceed normally, the Tiger is born from Water. He further stated: To know the art of reversal, mutual overcoming is mutual generation. He also stated: To know the origin of reversal lies in Li (Fire/Trigram) and Kan (Water/Trigram); one must recognize floating and sinking to determine host and guest. The *Caotang Ge* (Song of Thatched Cottage) says: If you wish to learn longevity, you must first understand the Five Elements. If the Five Elements are not reversed, the Return Elixir (Huan Dan) cannot be formed. Understanding the reversal of the Five Elements reveals that benefit contains harm, and harm transforms into benefit. Luozi said: Often seeing auspiciousness within ominous signs, auspiciousness often precedes the ominous. As the *Yinfu Jing* states: Heaven has five thieves; those who perceive them prosper. Observing heaven, earth, and all things, nothing is not reversed. However, one must recognize the true Five Elements to comprehend the art of reversal. Cao Zhenren said: The Five Elements are everywhere; does the Perfected One hoard them? To know the truth of the Five Elements, look to one water and one stone. Zheng Zhenren said: One Yin and one Yang is called the Dao; one water and one stone is called the Elixir. Another song states: To obtain the Metal within Lead, and simultaneously the Water within Stone. Essentially, Metal emerges from Water, and fluid emerges from Stone.