When the pregnant woman is going to the toilet, if her husband calls out to her suddenly from behind and she instinctively turns her head to the left, it indicates a male fetus; if she turns her head to the right, it indicates a female fetus. This is because the male fetus conceives in the left uterus, while the female fetus conceives in the right uterus. When the male fetus is on the left, the left side becomes heavier; thus, when turning her head, she instinctively protects the heavier side by leaning towards the left. When the female fetus is on the right, the right side becomes heavier; thus, when turning her head, she instinctively protects the heavier side by leaning towards the right. Applying this principle to pulse diagnosis (Mai Zhen), the logic remains the same. If the fetus is on the left, Qi and Blood (Qi Xue) protect the fetus and become abundant on the left; consequently, the pulse reflects this, with a rapid pulse on the left indicating a male, and a large pulse on the left also indicating a male. If the fetus is on the right, Qi and Blood protect the fetus and become abundant on the right; consequently, the pulse reflects this, with a rapid pulse on the right indicating a female, and a large pulse on the right also indicating a female. The Classic states: "When the Yin pulse beats vigorously and is distinct from the Yang, it signifies pregnancy." This means that since conception occurs below the navel and abdomen, Qi and Blood protect the fetus and become abundant in the lower part; therefore, the Chi pulse (associated with Yin) beats vigorously and is distinctly different from the Cun pulse (associated with Yang). Similarly, if an abscess or boil appears on the upper body, Qi and Blood flow upwards, causing the Cun pulse to be vigorous; if it appears on the lower body, Qi and Blood flow downwards, causing the Chi pulse to be vigorous; if it appears on the left, Qi and Blood flow to the left, causing the left pulse to be vigorous; if it appears on the right, Qi and Blood flow to the right, causing the right pulse to be vigorous.