Samadhi True Fire.

Samadhi True Fire 三昧真火 is an important idea in Neidan still used today by some schools. One Taiwan Xian Dao practitioner I met in Taipei used this as a central idea in his practice and it is one of the dominant theories of how the heart, kidneys and bladder generate the possibility of the opening of the Du Meridian in meditation. The idea is a little archaic but important to know since it had an outsized effect on Neidan. If you want to learn all about it please subscribe to read the whole explanation!

吕曰：“所谓造化，使阳长阴消，金丹可成而胎仙自化者，何也？”

Lu Asked: in regard to creation and transformation, the Golden Elixir forms and the Fetus Immortal transforms, how does this work?

钟曰：“人之心肾相去八寸四分，乃天地定位之比。气液太极相生，乃阴阳交合之比也。

Zhong said: people's hearts and kidneys are eight cun and four fen apart, heaven and earth's distance can be compared to this.

Qi and fluid are both generated of each other in the absolute extreme (Taiji) and Yin and Yang mix and join here.

一日十二时，乃一年十二月之比也。心生液，非自生也，因肺液降而心液行。液行夫妇，自上而下，以还下田，乃曰妇还夫宫。肾生气，非自生也，因膀胱气升而肾气行。

One day has twelve times, this can be compared to the twelve months of one year. The heart generates fluid, it does not do so by itself. It is because the lung fluid descends and causes the heart fluid to move, the fluid moves between husband and wife and goes from upper to lower, arriving at the Lower Dantian. This is the wife returning to the husband palace. The kidneys generate Qi, they do not do so by themselves, it is because of the bladder that the Qi rises and the kidney Qi moves.

气行子母，自下而上以朝中元，乃曰夫还妇室。

The Qi moves the son and mother, from lower to upper they arise the central origin, this is the husband returning to the wife palace.

肝气导引肾气，自下而上以至于心。心，火也，二气相交薰蒸于肺，肺液下降，自心而来皆曰心生液，以液生于心而不耗散，故曰真火也。

The liver Qi draws in the kidney Qi, from lower to upper it arrives at the heart. The heart is fire, the two types of Qi steam in the lung, the lung fluid descends and the heart can generate fluid. After the fluid is generated in the heart it does not scatter, this is called true fire.

肺液传送心液，自上而下以至于肾。肾，水也，二水相交，浸润膀胱，膀胱气上升，自肾而起者皆曰气，以气生于肾而不消磨，故曰真火也。

The lung fluid is transferred to the heart fluid, it goes from upper to lower and arrives at the kidneys. The kidney water has two waters which meet, they smooth the bladder and the bladder Qi rises up, then the kidneys rise and this is called Qi, this Qi is generated in the kidneys and does not get worn away, this is called true fire.

真火出于水中，恍恍惚惚，其中有物。视之不可见，取之不可得也。真水出于火中，杳杳冥冥，其中有精。见之不能留，留之不能往也。”

true fire leaves the water center, it is unclear and obscure, its center has being.

Look at it cannot be seen, grasp and it cannot be held. The true water comes from the center of fire, it is dark and deep, its center has essence. See it and it does not stay, if it stays it will not travel.

Explanation: