草衣子歌曰∶采炼铅汞在午前，一阴生即破其干。所以修生之士，阳时则服气，午后只闭息
而已。所以炼阴也。《赤城记》所谓炼气者，闭息也。闭息千日，则五脏不交、六腑不传、百脉不行、
百关自凑、神气自御、万化自定。天地不能盗其体，阴阳不能衰其形。从一至十，从十至百，
从百至千，闭息一百二十为小乘，闭息一千二百为中乘，闭息一万二千为大乘。昼夜计一万三千五百
息，呼吸计五百四十动为一息，去仙不远矣。其术∶湛然无思，澄心燕坐，昂头瞑目闭息，以右手
第二指第三指节，谓之生死门，受神之所，乃以数珠按之，心默数之。息急即右转咽喉，不
可令大急，急则微出外气，复吸则上。此在口诀。
胎息者，抱一守中之法也。婴儿在腹中，取气于脐管。十月脱胎，即取气于神庐。真人鼻无
出入，其息深深。老子所谓复归于婴儿者，胎息之谓也。《胎息歌》云∶鼻口非呼吸，方为胎息功。
虽居宇宙内，如在胞胎中。世人为生门有脐盖闭塞，所以气出不得。脐虚之后，求息则息，
自然气从此处出，鼻中无息也。蟠足正坐，两手交在脐上者，为脐虚。存一之后，应从此处出也。
圣胎内结，握固凝然。卫生之经，思过半矣。自子至午为炼阳，自午至酉为炼阴。阳主乎动，
阴主乎静。阳不欲溢，阴不欲覆。阴平阳秘，精神乃治。然而知之非难，持之在久无间断。与道相应
则内外俱进，而还丹之事可议矣。
《谷神论》∶含津炼气，吐故纳新，上入泥丸，下注丹田，谓之内丹。阳龙阴虎，木液金精，
二气交会，烹炼而成，谓之外丹。修道之人，先成内丹，后炼外药，内外相应，即致神仙。烟萝
子云∶真外应，丹自来。金华山人云∶只修真气不修丹，到了多应变化难。定机子亦云∶虽
是长生客，未为拔宅仙。更须修大药，方始得飞仙。
草衣子歌诀说：采炼铅汞要在午前进行，一阴初生时就要破除其刚干之性。所以修道养生的人，在阳气旺盛的时辰就服用元气（通过呼吸吐纳），午后则只闭住气息而已。这是为了炼化阴气。《赤城记》所说的炼气，就是闭息。闭息修炼一千天，就能做到五脏不相互交通、六腑不相互传递、百脉不运行、百关自然汇聚、神气自我驾驭、万物化育自然安定。天地不能窃取他的形体，阴阳不能衰败他的身形。从一到十，从十到百，从百到千，闭息一百二十次为小乘功法，闭息一千二百次为中乘功法，闭息一万二千次为大乘功法。昼夜计算共有一万三千五百息，呼吸计五百四十动算作一息，这样距离成仙就不远了。具体方法：心境湛然没有杂念，澄澈心灵端正静坐，昂起头闭上眼睛闭住气息，用右手食指和中指的第二个指节，称为生死门，是受纳神气的地方，然后用数珠按压此处，心中默计数目。气息急促时就向右转动咽喉部位，不可以让气息过于急促，急促了就会微微呼出外气，再次吸气时气息就会上升。这在口诀中有所记载。
胎息，是抱守一中、持守中道的法门。婴儿在母腹中，从脐带获取气息。十月期满脱胎后，就从神庐（鼻窍）获取气息。真人鼻子没有气息出入，他们的呼吸深沉细微。老子所说的“复归于婴儿”，指的就是胎息。《胎息歌》说：鼻口不再进行常规呼吸，这才是胎息的功夫。虽然居住在宇宙之内，却如同处在胞胎之中。世人因为生门有脐盖闭塞，所以气息无法从此处出来。待脐部虚灵之后，寻求气息，气息自然会从此处出来，而鼻子中就没有气息出入。盘腿端正静坐，两手交叉放在脐上，这叫作使脐部虚灵。存守真一之后，气息应该从此处出来。
圣胎在体内凝结，手握固拳，神态凝定。养生的要领，思考到这里已经过半了。自子时至午时为炼化阳气，自午时至酉时为炼化阴气。阳气主司运动，阴气主司静止。阳气不希望过度充盈，阴气不希望过度覆盖。阴气平和、阳气秘固，精神才能调治。然而知道这些并不难，关键在于长久坚持且不间断。与道相应，则内外共同进步，还丹之事就可以商议了。
《谷神论》说：含藏津液炼化气机，吐出故旧纳入新鲜，气向上进入泥丸宫，向下注入丹田，这叫做内丹。阳龙阴虎，木液金精，二气交会，烹炼而成，这叫做外丹。修道之人，先成就内丹，后炼化外药，内外相应，就能达到神仙境界。烟萝子说：真气真正相应，丹药自然到来。金华山人说：只修真气不修丹，到了最后往往变化困难。定机子也说：虽然是长生客，还未成为拔宅升仙的仙人。还必须修炼大药，才开始能够飞天成仙。
The song of Caoyizi states: Collecting and refining Lead and Mercury (Qian Gong, 铅汞) must be done before noon; when the first Yin arises, one should break its rigidity. Therefore, those who cultivate life take in Qi (vital energy) during Yang hours, and after noon, they only practice breath retention (breath-holding). This is to refine Yin. As stated in *Chicheng Ji*, refining Qi refers to breath retention. After practicing breath retention for a thousand days, the Five Zang organs will not interact, the Six Fu organs will not transmit, the hundred vessels will not flow, the hundred gates will naturally converge, Shen (spirit) and Qi will self-govern, and all transformations will naturally settle. Heaven and Earth cannot steal his body, and Yin and Yang cannot decay his form. From one to ten, from ten to a hundred, from a hundred to a thousand, retaining breath for 120 times is the Lesser Vehicle (Xiao Cheng), for 1,200 times is the Middle Vehicle (Zhong Cheng), and for 12,000 times is the Greater Vehicle (Da Cheng). Calculating day and night, there are 13,500 breaths; counting 540 movements of respiration as one breath brings one close to immortality. The technique is as follows: Be clear and thoughtless, purify the mind and sit upright, raise the head, close the eyes, and retain breath. Use the second interphalangeal joint of the right hand's index and middle fingers, known as the Gate of Life and Death (Sheng Si Men), which is the place where Shen receives Qi. Press this area with a rosary bead and count silently in the heart. If the breath becomes urgent, rotate the throat to the right; do not let it become too urgent, for urgency causes external air to escape slightly, and upon inhalation, the Qi rises again. This is recorded in the oral instructions.
Fetal breathing (Tai Xi) is the method of embracing the One and guarding the Center. When an infant is in the womb, it draws Qi from the umbilical cord. After ten months of shedding the fetal state, it draws Qi from the Shen Lu (Spirit Loft, i.e., the nasal cavity). A True Person has no inhalation or exhalation through the nose; their breath is deep and subtle. What Laozi referred to as "returning to the state of an infant" denotes fetal breathing. The *Fetal Breathing Song* states: "When the nose and mouth cease ordinary respiration, then the work of fetal breathing begins. Though dwelling within the universe, one is as if within the amniotic sac." Ordinary people have their birth gate blocked by the navel cover, so Qi cannot exit from there. Once the navel becomes empty/virtual, seeking Qi allows it to naturally emerge from this point, while there is no Qi movement in the nose. Sitting cross-legged and upright, with hands crossed above the navel constitutes making the navel virtual. After preserving the One, Qi should emerge from this point.
The Sacred Embryo forms internally, with fists clenched tightly and demeanor serene. The essence of health preservation has been half understood here. From Zi hour to Wu hour is the refining of Yang; from Wu hour to You hour is the refining of Yin. Yang governs movement, and Yin governs stillness. Yang should not overflow, and Yin should not cover excessively. When Yin is peaceful and Yang is secure, Spirit and Qi are regulated. However, knowing this is not difficult; the difficulty lies in persisting without interruption for a long time. Aligning with the Dao leads to simultaneous progress inside and out, and the matter of returning elixir can then be discussed.
*Gushen Lun* states: Containing saliva and refining Qi, expelling the old and absorbing the new, with Qi ascending to Niwan Palace (Mud Pill, located at the top of the head) and descending to Dantian (Elixir Field), is called Internal Elixir (Nei Dan). Yang Dragon and Yin Tiger, Wood Fluid and Metal Essence, intersecting and refining each other, is called External Elixir (Wai Dan). Those who cultivate the Dao first achieve the Internal Elixir, then refine External Medicine; when internal and external correspond, one attains immortality. Yanluozi said: "When true Qi truly corresponds, the Elixir arrives naturally." Jinhua Shansheng said: "If one only cultivates true Qi and does not cultivate the Elixir, changes at the end will often be difficult." Dingjizi also said: "Although one is a guest of longevity, one has not yet become an immortal who lifts the entire house to heaven. One must further cultivate the Great Medicine to begin flying to immortality."