用物之精，取物之华。集我丹田，我丹所家，我丹伊芳何。铅汞丹砂，客主相守，如巢养
鸦。种以戊已，耕以亦蛇，养以丙丁，灌以河车。乃根乃株，乃蕊乃花，昼炼于火，赫然彤
霞
人之所以生死，未有不自坎离者。坎离交则生，分则死，必然之道也。离为心，坎为肾。
心之所然，未有不正。虽桀跖亦然其所以为桀跖者，以内轻而外重。故常行其所不然者尔，
肾强而溢。则有欲念，虽尧颜亦然。其所以为尧颜者，以内重而外轻。故常行其所然者尔。
由此观之，心之性，法而正。肾之性，淫而邪，水火之德固如是也。子产曰∶火烈人望而畏
之，水弱人狎而玩之，达者未有不知此者也。龙者汞也，精也血也，出于肾而肝藏之，坎之
物也，虎者铅也。气也，力也。出于心而肺主之，离之物也。心动，则气随之而作，肾溢则
精血随之而流。如火之有烟 ，未有复反于薪者也。世之不学道者，其龙常出于水。故龙飞
而汞轻，其虎出于火。故虎走而铅枯，此生人之常理也。顺此者死，逆此者仙。故真人之言
曰∶顺行则为人，逆行则为道。又曰∶五行颠倒术，龙从火里出。五行不顺行，虎向水中生。
有隐者教予曰∶人能正坐瞑目，调息，握固，心定，微息则徐闭之。（达磨胎息法亦须闭若
此，佛经待其自止，恐卒不能到也）虽无所念，而卓然精明。毅然刚烈，如火之不可犯。息
极则小通之，微则复闭之。（方其通时亦须一息一息扫之下丹田）为之惟数，以多为贤，以
久为功。不过十日，则丹田温而水上行。愈久愈温，几至如烹。上行水。翕然如云蒸于泥丸，
盖离者丽也。着物而见，火之性也。吾目引于色，耳引于声。口引于味，鼻引于香，火辄随
而丽之。今吾寂然无所引于外，火无所丽。则将安往，水者其所妃也。势必从之，坎者陷也。
物至则受，水之性也，而况其配乎？水火合，则火不炎而水自上。则所谓龙从火里出也。龙
出于火，则龙不飞而汞不干。旬日之外，脑满而腰足轻。方闭息时常卷舌而上。以舐县雍虽
不能，而意到焉，久则能也。如是不已，则汞下入口。方调息时，则漱而烹之，须满口而后
咽。若未满，且留口中，俟后次也，仍以空气送至丹田。常以意养之，久则化而为铅，此所
谓虎向水中生也。此论奇而通，妙而简，决为可信者。然吾有大患，平生发此志愿百十回矣，
皆缪悠无成意，此道非捐躯以赴之，刳心以受之，尽命以守之，不能成也。吾今年已六十，
名位破败，兄弟隔绝，父子离散。身居蛮夷。北归无日，区区世味，亦可知矣。若复缪悠于
此。真不如人矣，故数日来，别发愿愿，譬如古人避难穷山，或使绝域，啮草啖雪，彼何人
哉？已令造一禅榻两大案，明窗之下，即专欲治此，并已作干蒸饼百枚，自二月一日为首，
尽绝人事。饥则食此饼，不饮汤水，不啖他物。细嚼以致津液，或饮少酒而已。午后略睡，
一更卧，三更乃起，坐以达旦，有日采日，有月采月，余时非数息炼阴则行，今所谓龙虎诀
耳。如此百日，或有所成，不读书，不看经，且一时束起，以待异日，不游山水，除见道人
外，不接客，不会饮，皆无益也。深恐易流之性，不能终践此言，故先作书以报。庶几他日
有惭于弟，而不敢变也。此事大难，不知其果然能不惭否。此书既以自坚，又欲以发弟也。
养舌以舐县雍，近得此法。初甚秘惜，云此禅家所得向上一路，千金不传，人之所见如此虽
可笑，然极有验也。但行之数日间，舌下筋微急痛，当以渐驯致。若舌尖果及悬雍，则致华
池之水莫捷于此也。又言此法名洪炉上一点雪，宜秘之。
运用万物的精华，采集事物的华彩。汇聚于我的丹田，那是金丹的居所，我的金丹究竟在哪里呢？铅、汞、丹砂，作为客与主相互守护，如同鸟巢中养育乌鸦一般。以戊己土来播种，以巳蛇（地支）来耕作，以丙丁火来滋养，以河车（精气运行之路）来灌溉。于是有了根和株，有了蕊和花，白天用火炼制，呈现出鲜艳的彤霞景象。
人之所以有生死，没有不是由坎离二卦决定的。坎离相交则生，分离则死，这是必然的道理。离卦对应心，坎卦对应肾。心的本性，没有不端正的。即使是夏桀、盗跖这样的人，他们之所以成为桀跖，是因为内心轻浮而外表庄重，所以常常做一些不符合本性的事情罢了；肾气强盛而满溢，就会产生欲念，即使是尧帝、颜回这样的人也是如此。他们之所以成为尧颜，是因为内心庄重而外表轻灵，所以常常顺应本性行事。由此看来，心的本性，效法天道而端正；肾的本性，淫逸而邪僻，水火的本德本来就是这样的。子产说：“火猛烈，人们望而生畏；水柔弱，人们亲近并玩弄它。”通达事理的人没有不知道这一点的。龙就是汞，也是精，也是血，出于肾而由肝收藏，属于坎卦之物；虎就是铅，也是气，也是力，出于心而由肺主宰，属于离卦之物。心动，气就随之发动；肾气满溢，精血就随之流动。就像火有烟一样，烟没有再回到柴薪中的道理。世上那些不修道的人，他们的“龙”经常从水中出。所以龙飞腾而汞变轻，他们的“虎”从火中出。所以虎奔走而铅枯竭，这是常人的生理常态。顺着这个规律就会死，逆着这个规律就能成仙。所以真人说：“顺行则为人，逆行则为道。”又说：“五行颠倒术，龙从火里出。五行不顺行，虎向水中生。”
有一位隐士教我道：“人能正身端坐，闭上眼睛，调节呼吸，握固手指，心神安定，气息微弱时慢慢闭住。（达摩胎息法也需要这样闭气，佛经说等待气息自然停止，恐怕很难达到那个境界。）虽然没有什么念头，但精神卓然精明，意志毅然刚烈，像火一样不可侵犯。气息极尽时稍微疏通一下，微弱时再次闭住。（在疏通的时候，也需要一呼一吸地清扫下丹田。）这样做只在于计数，以多为贤，以持久为功。不超过十天，丹田就会温暖而上行的水液随之上升。时间越久越温暖，几乎像烹煮一样。上行之水，聚集成云蒸雾绕状在泥丸宫（脑部）。离卦意为附着，接触事物而显现，这是火的特性。我的眼睛被颜色牵引，耳朵被声音牵引，口被味道牵引，鼻被香气牵引，火就随即附着在这些感官上。现在我寂静无为，不被外物牵引，火就没有附着点。它将去哪里呢？水是它的配偶。势必要跟随它，坎卦意为陷落，事物到来就承受，这是水的特性，何况是它的配偶呢？水火相合，火就不炎上而水自上行，这就是所谓的‘龙从火里出’。龙从火中出，龙就不飞腾而汞不干涸。过了十天左右，头脑充实而腰脚轻便。在闭气时常卷起舌头向上舔舐悬雍垂（小舌），虽然做不到，但意念要到那里，久了就能做到。像这样不停止，汞就会下行进入口中。在调节呼吸时，就漱口并烹炼它，必须满口才吞咽。如果没满，暂且留在口中，等到下一次，仍以空气送至丹田。常用意念温养它，久了就化为铅，这就是所谓的‘虎向水中生’。这个理论奇特而通达，微妙而简练，确实可信。
然而我有个大忧患，平生发下这个志愿上百十次了，都荒谬悠远而无成果。这道非但不能牺牲生命去奔赴，剖开心胸去接受，耗尽性命去坚守，是不能成功的。我今年已经六十岁，名声地位破败，兄弟隔绝，父子离散，身体居住在蛮夷之地，北归无期，世俗的滋味也就可想而知了。如果再在这上面荒谬悠远，真不如常人。所以这几天重新发誓，譬如古人避难于穷山，或流放绝域，啃草吃雪，他们是些什么人呢？我已经让人造了一张禅榻和两张案几，在明亮的窗下，专门想要研究此道，并且已经制作了干蒸饼一百个，从二月一日开始，彻底断绝人事往来。饿了就吃这些饼，不喝汤水，不吃其他东西。细细咀嚼直到津液产生，或者喝一点酒而已。午后稍微睡一会儿，一更天躺下，三更天起来，坐着直到天亮。有时采日精，有时采月精，其余时间如果不是数息炼阴，就是行走，这就是现在所说的龙虎诀。如此坚持百日，或许会有所成就。不读书，不看经，暂时束之高阁，留待异日；不游山玩水，除了见道人外，不见客人，不聚会饮酒，这些都无益。深深担心自己容易流俗的本性，不能最终践行此言，所以先写信告知。希望将来对弟弟感到惭愧，而不敢改变。这件事非常困难，不知道是否真的能不感到惭愧。这封信既用来坚定自己的信念，又想启发弟弟。
用舌头舔舐悬雍垂来养护舌头，最近得到了这个方法。起初非常秘惜，说是禅家所得的向上一路法门，千金不传，人们的见识竟然如此，虽然可笑，但极其有效。只是施行几天后，舌下的筋脉微急痛，应当逐渐驯服适应。如果舌尖果然能触及悬雍垂，那么获取华池之水（唾液）没有比这更快捷的了。又说这个方法名叫‘洪炉上一点雪’，应该保密。
Utilizing the essence of all things, gathering the splendor of objects. Collecting into my Dantian (Lower Elixir Field), where my Dan (Elixir) resides, what is this Dan of mine? Lead (Qian), Mercury (Yin), and Cinnabar, guest and host guarding each other, like a nest raising crows. Sown with Wu-Ji (Earthly Stems), cultivated with Yi-She (Earthly Branches), nourished with Bing-Ding (Fire), irrigated with Heche (River Cart/Energy Path). Thus there are roots and stems, pistils and flowers; refined by fire during the day, blazing with red clouds.
The reason for human life and death lies none other than in Kan (Water/Kidney) and Li (Fire/Heart). When Kan and Li interact, there is life; when they separate, there is death; this is an inevitable principle. Li corresponds to the Heart, Kan corresponds to the Kidneys. The nature of the Heart is invariably upright. Even figures like Jie and Zhi (tyrants/thieves), insofar as they became such, did so because their inner self was frivolous while their outer appearance was solemn; thus they often acted contrary to their true nature. The Kidneys become strong and overflow, generating desires; even sages like Yao and Yan Hui are subject to this. However, insofar as they became sages, it was because their inner self was solemn while their outer appearance was light; thus they often acted in accordance with their nature. From this we see: the nature of the Heart follows the Way and is upright; the nature of the Kidneys is licentious and deviant; the virtues of Water and Fire are inherently thus. Zichan said: "Fire is fierce, and people fear it at the sight; Water is weak, and people play with it." Those who understand do not fail to know this. Dragon refers to Mercury, Essence, and Blood; it originates from the Kidneys and is stored by the Liver, belonging to Kan. Tiger refers to Lead, Qi, and Strength; it originates from the Heart and is governed by the Lungs, belonging to Li. When the Heart moves, Qi follows and arises; when the Kidneys overflow, Essence and Blood follow and flow. Just as fire produces smoke, smoke does not return to the firewood. In the world, those who do not practice the Dao have their Dragon constantly emerging from Water. Thus the Dragon flies and Mercury becomes light; their Tiger emerges from Fire. Thus the Tiger runs and Lead withers; this is the common logic of ordinary humans. Following this leads to death; reversing this leads to immortality. Hence the True Person says: "Proceeding forward makes one human; proceeding backward makes one the Dao." It also says: "The art of reversing the Five Elements: Dragon emerges from Fire. The Five Elements do not proceed normally; Tiger is born from Water."
A hermit taught me: "One can sit upright, close the eyes, regulate the breath, hold the fingers in a fist (Wogu), calm the mind, and when the breath becomes faint, slowly close it. (Dharma's Fetal Breathing method also requires closing the breath like this; Buddhist scriptures suggest waiting for it to stop naturally, which is likely difficult to achieve.) Although having no thoughts, one remains distinctly lucid and resolute, fierce like fire that cannot be violated. When the breath reaches its limit, open it slightly; when faint, close it again. (When opening, one must also sweep the Lower Dantian with each breath.) This practice relies on counting; more is better, longevity is the merit. Within ten days, the Dantian will warm up and water will rise. The longer, the warmer, almost like boiling. The rising water gathers like steam in the Niwan Palace (Brain). Li means attachment; appearing upon contact with objects is the nature of Fire. My eyes are led by colors, ears by sounds, mouth by tastes, nose by scents; Fire attaches to these accordingly. Now I am silent and unled by externals; Fire has nothing to attach to. Where will it go? Water is its consort. It will inevitably follow it. Kan means陷陷 (trap/sink); receiving objects is the nature of Water, especially its consort? When Water and Fire combine, Fire does not blaze upward, and Water rises from above. This is called 'Dragon emerges from Fire.' When Dragon emerges from Fire, it does not fly and Mercury does not dry up. After ten days, the head feels full and waist/legs feel light. During breath retention, roll the tongue up to lick the uvula. Though physically difficult, intent must reach there; with time, it becomes possible. If continued without cessation, Mercury descends into the mouth. While regulating breath, rinse and refine it, swallowing only when the mouth is full. If not full, retain it in the mouth for the next session, then send it to the Dantian with air. Nourish it with intent; over time, it transforms into Lead. This is called 'Tiger born from Water.' This theory is strange yet logical, subtle yet simple, and certainly credible.
However, I have a great worry. I have made this vow dozens of times in my life, but all were vague and fruitless. This Dao cannot be achieved unless one dedicates one's life to it, opens one's heart to receive it, and guards it with one's existence. I am now sixty years old, my reputation and status ruined, brothers separated, father and son scattered, living among barbarians, with no hope of returning north. The flavors of the secular world are clear enough. If I remain vague here, I would be worse than ordinary people. Therefore, recently I have renewed my vows, like ancients fleeing to mountains or exiled to remote lands, gnawing grass and eating snow—who were they? I have ordered a meditation mat and two desks built, under bright windows, specifically to study this. I have also prepared one hundred dried steamed cakes. Starting February 1st, I will completely cut off social interactions. Hungry, I eat these cakes; I drink no soup or water, nor eat anything else. Chew finely until saliva is produced, or drink a little wine. Sleep briefly after noon, lie down at first watch, rise at third watch, sit until dawn. Sometimes gather Sun Essence, sometimes Moon Essence; otherwise, if not counting breaths to refine Yin, I walk. This is the current Dragon-Tiger Method. Persisting for a hundred days may yield results. No reading books or scriptures, putting them aside for later; no touring landscapes; seeing no guests except Daoist priests; no drinking gatherings—all are useless. I deeply fear my fickle nature will not allow me to fulfill this promise, so I write this letter first. Perhaps someday I will feel ashamed before my brother and dare not change. This matter is very difficult; I do not know if I will truly succeed without shame. This letter serves to strengthen my resolve and inspire my brother.
Nourishing the tongue to lick the uvula is a recent method. Initially kept secret, claimed as the highest path of Zen, not transmitted for a thousand gold. People's views are indeed limited; though laughable, it is extremely effective. However, after a few days of practice, the tendons under the tongue become slightly tight and painful; one must gradually adapt. If the tip of the tongue can indeed touch the uvula, there is no quicker way to obtain the Water of the Hua Chi (saliva). It is also said this method is named 'A Drop of Snow on a Great Furnace' and should be kept secret.