《黄帝内经·素问·调经论》
病生于阳经在表的，都是感受了风雨寒暑邪气的侵袭；病生于阴经在里的，都是由于饮食不节、起居失常、房事过度、喜怒无常所致。
其生于阳者，得之风雨寒暑；其生于阴者，得之饮食居处，阴阳喜怒。
The diseases in the Yang Jing, which are on the surface of the body, are all caused by the invasion of the evil Qi of wind, rain, cold and heat. The diseases in the Yin Jing, which are in the body, are all caused by irregular diet, irregular life, excessive sexual intercourse, and irregular joy and anger.