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Cheng Mingqian stated: Chu Cheng claimed that during sexual intercourse, if the yin blood arrives first and the yang essence follows to enter, a male fetus is formed; if the yang essence enters first and the yin blood subsequently joins, a female fetus is formed. If one believes this statement, why do some people who ejaculate semen first give birth to sons, while those who ejaculate later give birth to daughters? Li Dongyuan said: One or two days after menstruation ceases, the Blood Sea (Xue Hai) has just cleared; conception at this time results in a male. By the fourth or fifth day, the blood vessels are already vigorous; conception at this time results in a female. After the sixth or seventh day, even if sexual intercourse occurs, pregnancy cannot be achieved. If one believes this statement, why do some women conceive daughters immediately after menstruation ends, but conceive sons only after a long period post-menstruation? Why is it that some fail to conceive when having intercourse before the fourth or fifth day after menstruation ends, yet succeed when doing so after the eighth or ninth day? Yu Ziben wrote *Guang Si Yao Lue* (Essentials for Prolonging Offspring), prescribing formulas and drawing diagrams, asserting that "solid yang can enter hollow yin, but solid yin cannot receive yang," which is merely an old view of Li Dongyuan. He further stated that "weak yang cannot shoot into yin, and weak yin cannot grasp yang." If one believes this, why are there frail husbands and timid, weak wives who frequently conceive, unable to stop despite wanting to? Conversely, why are there individuals with robust qi and blood and superior vitality who struggle to produce offspring and cannot be saved? Zhu Danxi's discussion on treatment focuses primarily on women's menstruation. However, among wealthy families with many concubines, are there not those whose menstrual periods are regular? Some marry women who have frequently borne children by previous husbands, thinking it will be easy to conceive, yet they fail to get pregnant. When these women are remarried to others, they quickly bear sons. Is it possible that they cannot conceive here but can conceive elsewhere?

I believe that parents giving birth to children is like heaven and earth generating all things. The *Yi Jing* (Book of Changes) states: "The way of Earth is its docility, receiving from Heaven and acting according to the seasons." Since we know that Earth generates all things by simply following and receiving from Heaven, we should understand that mothers giving birth to children also simply follow and receive from fathers. Knowing that mothers follow and receive from fathers, does the process of conceiving depend primarily on the woman or the man? However, regarding the primacy of the man, it does not matter whether he is young or old, strong or weak, healthy or sickly, prone to premature ejaculation or able to retain semen. The key is whether, at the moment of sexual intercourse, the "hundred pulses arrive together" (Bai Mai Qi Dao). If the hundred pulses arrive together during intercourse, even an old, weak, sickly person prone to ejaculation can achieve conception. If the hundred pulses are disordered during intercourse, even a young, strong, healthy person capable of retaining semen will find it difficult to conceive. The blood gathered by the woman is indeed due to the convergence of the hundred pulses, yet compared to the man's essence, there must be a distinction in weight and importance. Confucius praised the Qian Yuan (Heavenly Origin) for initiating creation as "Great," and praised the Kun Yuan (Earthly Origin) for nourishing life as "Ultimate." Does this not imply something profound?

Regarding the differentiation between male and female fetuses, it is not determined by the sequence of essence and blood arrival, nor by how many days after menstruation cessation, nor by whether intercourse occurs before or after midnight, nor by whether the father is stronger than the mother or vice versa. It is solely determined by whether the essence and blood respectively arrive together via the hundred pulses, which decides the outcome. Therefore, if the arrival of the hundred pulses in the essence surpasses that of the blood, a male is formed. If the arrival of the hundred pulses in the blood surpasses that of the essence, a female is formed. As for those who suffer miscarriage after conception, those who give birth but cannot raise the child, those who raise the child but have a short lifespan, or those who live long but have no descendants, these outcomes are also determined by the firmness or fragility of the essence and blood, which dictates longevity. People of the world fail to observe that the firmness or fragility of their essence and blood was established at the very beginning of their endowment. Yet, they blame the mother exclusively for miscarriage, attribute the failure to raise the child to the son, and dismiss longevity or early death to fate. Is this not absurd?