《褚氏遗书》曰∶男女之合，二情交畅，阴血先至，阳精后充，血开裹精，精入为骨，而男形成。阳精先入，
阴血后参，精开裹血，血入居本，而女形成。
《圣济经》曰∶天之德，地之气，阴阳至和，流薄一体。因气而左动则属阳，阳资之则成男。因气而右动
则属阴，阴资之则成女。《易》称干道成男，坤道成女。此男女之别也。
李东垣曰∶经水断后一二日，血海始净，精胜其血，感者成男。四五日后，血脉已旺，精不胜血，感者成
女。至六七日后，虽交感亦不成胎。
朱丹溪曰∶《易》云∶干道成男，坤道成女。夫乾坤，阴阳之性情也。左右，阴阳之
道路也。男女，阴阳之仪象也。父精母血，因感而会。精之泄，阳之施也。血能摄精，精成其骨。此万物之资始于干
元也。血之行也，精不能摄血成其胞。此万物之资生于坤元也。阴阳交媾，胚胎始凝。胎所居，名曰子宫。一
系在下，上有两歧，一达于左，一达于右。精胜其血，则阳为之主，受气于左子宫，而男形成。精不胜血，则
阴为之主，受气于右子宫，而女形成，孕成而始化胞也。
马玄台曰∶男子先天之气，方父母媾精时，阴气不胜其阳则成男。凡医书谓阴血先至，阳精后冲，纵气来
乘，血开裹精，阴外阳内则成男，其义亦渺。大约阴气不胜其阳，则为男。女子先天之气，方父母交媾时，阳
气不胜其阴，则为女。凡医书谓阳精先入，阴血后参，横气来助，精开裹血，阴内阳外则成女，其义亦渺。大约
阳气不胜其阴，则为女。
The *Chu Shi Yi Shu* (Remnant Books of Master Chu) states: When male and female unite, with mutual emotions flowing smoothly, if the Yin blood arrives first and the Yang essence follows to fill it, the blood opens to wrap the essence. The essence enters to form the bone structure, and the male fetus is formed. If the Yang essence enters first and the Yin blood subsequently participates, the essence opens to wrap the blood. The blood enters to reside in the root, and the female fetus is formed.
The *Sheng Ji Jing* (Holy Relief Classic) states: The virtue of Heaven (Yang Qi), the Qi of Earth (Yin Qi), reach a state of supreme harmony between Yin and Yang, flowing and blending into one entity. Due to Qi moving to the left, it belongs to Yang; nourished by Yang, it forms a male. Due to Qi moving to the right, it belongs to Yin; nourished by Yin, it forms a female. The *I Ching* (Book of Changes) states that the Dao of Qian forms males, and the Dao of Kun forms females. This is the distinction between males and females.
Li Dongyuan states: One or two days after menstruation ceases, the Blood Sea is just cleared. Essence surpasses blood; conception results in a male. Four or five days later, the blood vessels are vigorous, and essence cannot surpass blood; conception results in a female. By the sixth or seventh day, even if intercourse occurs, pregnancy will not be conceived.
Zhu Danxi states: The *I Ching* says: "The Dao of Qian forms males, the Dao of Kun forms females." Qian and Kun represent the nature of Yin and Yang. Left and right represent the pathways of Yin and Yang. Male and female represent the manifestations of Yin and Yang. The father's essence and mother's blood meet due to mutual influence. The emission of essence is the bestowal of Yang. Blood can retain essence, and essence forms its bones. This is why all things originate from the Primordial Qian. The movement of blood is such that essence cannot retain blood to form the Bao (uterus/womb). This is why all things are nurtured from the Primordial Kun. When Yin and Yang intertwine, the embryo begins to condense. The place where the embryo resides is called the Zi Gong (Uterus). There is a single cord below, branching above into two paths, one leading to the left and one to the right. If essence surpasses blood, Yang becomes dominant, receiving Qi in the left Zi Gong, and the male fetus is formed. If essence does not surpass blood, Yin becomes dominant, receiving Qi in the right Zi Gong, and the female fetus is formed. Only after pregnancy is established does the Bao transform.
Ma Xuantai states: Regarding the innate Qi of men, at the moment of parental union, if Yin Qi cannot overcome Yang Qi, a male is formed. Medical texts generally claim that if Yin blood arrives first and Yang essence follows, and when Zong Qi (Constitutional Qi) arrives to overpower, the blood opens to wrap the essence, resulting in Yin outside and Yang inside forming a male; this reasoning is obscure. Generally speaking, if Yin Qi cannot overcome Yang Qi, a male is formed. Regarding the innate Qi of women, at the moment of parental union, if Yang Qi cannot overcome Yin Qi, a female is formed. Medical texts generally claim that if Yang essence enters first and Yin blood participates, and when Heng Qi (Lateral Qi) assists, the essence opens to wrap the blood, resulting in Yin inside and Yang outside forming a female; this reasoning is also obscure. Generally speaking, if Yang Qi cannot overcome Yin Qi, a female is formed.