Excerpt from <span class="chinese-post-title">述郭雲深先生言</span> Report of Guō Yúnshēn Sayings in <span class="chinese-post-title">拳意述真</span> Boxing Concepts Explained Authentically

四則

神氣未交之時。存神用息。緜緜若存。念茲在茲。此武火之謂也。至神氣已交。又當忘息。以致採取歸爐。封固。停息。沐浴。起火。進退升降歸根。俟動而復煉。煉至不動。為限數足滿。止火。謂之坎離交妒。此為小周天。

郭雲深

"When spirit and energy are not yet joined, preserve your spirit and just work with your breath as if you will dwell in it forever, keeping your mind on it always. This is called the “martial fire”. Once spirit and energy are joined, you may then forget about the breath, so that it is now like you are sealing up a furnace to put the fire out, then cleaning it out in order to start a new fire. In advancing and retreating, ascending and descending, you are returning to your source. Wait for movement to happen and then work at it [“smelt it”], working it until it attains stillness, enough stillness to “suppress the fire”. This is called “fire and water envying each other” and is the work of using the microcosmic breathing to attain the macrocosmic breathing. [From there is achieved emptiness, from which is attained purity.]"

Excerpt from the translation by Paul Brennan, to be found in the Brennan Translation blog.