When a male reaches sixteen years of age, Tian Gui (the subtle substance promoting sexual development) arrives; when a female reaches fourteen years of age, Tian Gui also arrives. If sexual intercourse occurs too early, it damages Yuan Qi (Primordial Qi), which is the cause of premature death. When a male reaches sixty-four years of age, Tian Gui ceases; when a female reaches forty-nine years of age, Tian Gui also ceases. At this stage, Jing and Xue (Essence and Blood) are no longer generated. If sexual activity is not restrained, one shortens their own lifespan. The blood in the human body penetrates all bones and limbs. When sexual desire arises, the blood from the entire body converges at Ming Men (the seat of Kidney Yang/Mingmen Fire), transforms into Jing (Essence), and is ejaculated. (When conception occurs, the fetus inherits this Ming Men Fire to generate life; thus, Zhuangzi said: "Fire is transmitted, its end unknown.") Jing (Essence) is relied upon by Shen (Spirit) as fish rely on water. (Shen must attach to an object to have a basis for existence; thus, Guanyin Zi said: "Jing has no fixed form; Shen has no self-awareness." The Shurangama Sutra states: "The nature of fire has no self, relying on various conditions.") Qi relies on Jing like mist covers an abyss. Failing to practice moderation and conservation will lead to the withering of all meridians. Unrestrained sexual intercourse inevitably damages the Kidney's Yuan Qi. Even if ejaculation does not occur externally, the Jing has already left its palace. A few drops of true Jing will inevitably overflow along with the flaccidity of the penis, similar to how fire has...