The Chinese see everything in the world under two opposing aspects that alternate, yet complement each other. Yang is external, expansive, luminous, open, active. Yin is interior, enclosed, somber, passive, Thus, heat is Yang, cold is Yin. As applied to the analysis of the sympathetic nervous system, this thought discerns that the orthosym- pathetic system is Yang and the parasympathetic is Yin. According to the Chinese, the excessive vital energy of the sympathetic system (sympathicotonia) brings on illnesses by an excess of Yang, while excessive vital energy of the parasympathetic system (vagotonia) brings on illnesses by an excess of Yin.
Treatises on acupuncture describe with great precision the particular paths along the body’s surface and the points where the action of acupuncture is exerted. These descriptions are the result of several thousand years of experience. Though they do not correspond to anatomical facts well known to Western science, since they are based on Chinese anatomical studies that measure in terms of fingerbones and nails. The lines do not correspond with the actual paths of the nerves, or with those of the blood vessels. The hypothesis has been formulated that these lines pass over the outcropping points of minute nervous filaments of the sympathetic system.