"Women are Yin below and Yang above, while men are the exact opposite, Yang below and Yin above," Du Heng said softly. "Men's kidneys produce essence, and like women, there must be waste produced. But this waste can't follow the same path as the essence, right?
"Moreover, waste is produced constantly. If it were to go along with the essence, you wouldn't be able to handle it.
"Using the concept of transitioning from Yin to Yang, the waste in the male body has to go from bottom to top, but there's no exit at the top. So, what should be done?"
Du Heng pointed to his own chin as he spoke, "Look here, men's beards are the male equivalent of menstrual periods.
"So, when you treat a man, you can also look at his beard. If his beard is thick, it indicates that his qi and blood are circulating smoothly. If his beard is sparse, it means that his qi and blood are deficient and not circulating well."
