Rudiments of Acupuncture

"In disease one must differentiate between the external and the internal location of the pathogen. In acupuncture there are differentiations of deep or shallow insertion. If the illness is on the biao, or external, level, one should insert superficially; if on the internal level, one should insert more deeply. The location of the illness must be reached; but it is important not to insert too deeply so as to not injure the five zang organs. Inserting too shallowly, however, will not allow the physician to reach the area of illness, and the qi and blood can be disrupted, which allows an opportunity for pathogens to enter. Acupuncture performed without a guiding principle can be dangerous or damaging." -The Rudiments of Acupuncture, Nei Jing Chapter 50