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Essence is stored in the Kidney, which everyone knows. However, how essence is generated, how it is stored, and how it is discharged, people do not understand. Essence is the fat and paste within the Kidney. There are those that exist for a long time, and those that are produced daily. Within the Kidney, there is a place where essence is stored, full and lacking nothing, like water in a well, filling up day and night; this is the long-lasting essence. The essence discharged during sexual desire and intercourse, as well as the essence lost through sliding and leakage due to illness, is the daily-produced essence. The discharge and generation of essence alternate; if not discharged, it is not generated, just like water in a well: drawing from it daily does not show a decrease, and not drawing from it for a whole year does not show an overflow. The *I Ching* (Book of Changes) states: "The way of the well cannot remain unchanged, therefore it is followed by Ge (Revolution)," which illustrates this principle. One might ask: Does this mean indulging in lust causes no harm? The answer is: This is incorrect. Generally, the principles of the world return to nature. Those with abundant Kidney Qi can indulge without injury; those with declining Kidney Qi should naturally practice moderation and nourishment. The *Zuo Zhuan* asks: "Should women not be approached?" The reply is: "One must exercise restraint." If one indulges in lust without restraint, it is like a shallow and narrow well: drawing from it without limit will lead to depletion. One might ask: What about a robust person who completely abstains from sex? The answer is: This results in neither merit nor fault, merely making the Kidney Qi slightly more solid. However, one must ensure that floating fire does not move and that Yin and Yang guard each other. If floating fire moves daily but is forcibly suppressed, it will cause harm. Because essence leaves its proper position due to fire movement, symptoms such as dizziness, red eyes, body itching, lower back pain, seminal emission, and unilateral testicular swelling or descent will inevitably occur; some may even develop carbuncles and ulcers. These are the harms of forced suppression. Therefore, essence is such that it is generated when desire stirs, and not generated when it does not stir. Natural non-stirring is beneficial; forced suppression is harmful; overuse leads to exhaustion. Following nature without forcing oneself is the method for preserving essence. Laozi said: "There is no fixed law; the Dao follows nature." The way of nature is the secret to longevity.

Human death is generally determined by the presence or absence of Yuan Qi (Original Qi). Thus, when a person falls ill, their Yuan Qi is already injured, making the condition critical. When Yuan Qi escapes, the Five Zang and Six Fu organs all lose their Qi. Yet, there are cases where Yuan Qi is deeply rooted and stable, while internally one Zang or one Fu organ fails first. For example, Heart failure leads to confusion and unawareness of worldly affairs; Liver failure leads to uncontrolled anger and joy; Kidney failure leads to impotence; Spleen failure leads to inability to digest food; Lung failure leads to shortness of breath and hoarseness. The failure of the Six Fu organs, losing their respective functions, is also the same. The signs of their failure must have obvious visible manifestations. Generally, Qi still exists, but the spirit, consciousness, and essence cease to function; only a skilled physician can determine this. Among all Zang and Fu organs, Lung failure leads to death most rapidly. Because the Lung is the canopy (Huagai) of the Zang and Fu organs, and they rely on its Qi for nourishment, when this organ fails, the Zang and Fu organs receive no endowment. For the others, prognosis depends on the severity of the failure, the strength or weakness of other organs, and the state of post-heaven dietary intake. Based on these, one can determine auspiciousness or inauspiciousness, and thus predict the length of life. However, generally, it does not exceed one year. These observations are based on personal experience, not speculation.