When a man reaches the age of 28, the heavenly essence arrives; when a woman reaches 27, the Heavenly essence also arrives. If they have sexual intercourse too early, the heavenly essence will be lost, which is the reason for their premature death. When a man reaches the age of eighty-eight and his heavenly essence ceases to grow, or a woman reaches the age of seventy-seven and her heavenly essence ceases to grow, his vital energy and blood cease to be generated. Entering the room without restraint is a self-promotion of his longevity. The blood of the human body flows through all the bones. When one desires to do something, gather the blood of the entire body and place it at the life gate to transform into essence and release it. When a person is born, they are endowed with the fire of this life to give birth. Therefore, Zhuangzi said:... The essence is like a fish in water, with the spirit leaning on it, providing shade. Therefore, Guan Yinzi said, "The essence has no self, and the spirit has no self." The Shurangama Sutra states, "The nature of fire has no self and is dependent on various causes and conditions." The air is like a mist covering a deep abyss. If one does not practice frugality and restraint, all the meridians will become withered and the connection will be excessive, which will surely damage the kidney essence. Although the essence does not leak outwardly, it has already left the palace. There must be a few true essors that overflow with the loss of Yang, like the smoke of fire, how could they return to the stove!