"NAN Jing(难经 Nànjīng)," or "The Yellow Emperor's Canon of 81 Difficult Issues," is one of the most important classics of traditional Chinese medicine (TCM). It seeks to explain and clarify some seemingly unfathomable statements in "The Yellow Emperor's Inner Canon," the earliest surviving text on the theories and practices of TCM, dating back more than 2,300 years.

Some Chinese scholars claim that "Nan Jing" not only provides answers to difficult questions posed in "The Yellow Emperor's Inner Canon," but also to some from even earlier, long-lost Chinese medical texts, as a number of issues discussed are not found in the Inner Canon.

But one thing most Chinese scholars and historians are agreed upon is that "Nan Jing" made a significant contribution to the evolution of TCM in ancient China.

The book is composed of 81 chapters: chapters 1-22 discuss sphygmology - knowledge of the pulse; chapters 23-29 deal with channels and collaterals; chapters 30-47 explain viscera organs; chapters 48-61 study diseases and ailments; chapters 62-68 focus on acupoints; and the last 13 chapters explore acupuncture.

Through elaborate discussion and careful analyses, the book establishes a number of important concepts and theories, such as the life-gate and sanjiao (or triple body parts) concepts and the idea of the seven important portals - the digestive system. These laid a solid foundation for the further development of TCM theory.

It is believed that the book was authored by Qin Yueren, also known as Bian Que(扁鹊 biǎn què), who lived during the Warring States Period (475-221 BC).

Bian Que was originally the name of a fabled doctor during the reign of the mythical Yellow Emperor between 2697-2597 BC. But the name was given to Qin Yueren(秦越人 Qín Yuèrén), who is widely regarded as the first medical doctor and physician in ancient China.

Qin became an apprentice of a folk doctor when he was still a teenager and traveled with him at work. During the day, he carried out chores while watching closely how his master treated patients. At night, he jotted down what he had observed, as well as his own thoughts and conclusions.

Thanks to his appetite for learning and hard work, Qin soon became a very famous doctor and physician and became known as Bian Que, the highest honor for a doctor in ancient times.

In addition to the traditional medical skills he learned from other doctors and his own experiences, Bian Que also invented his own methods. These include founding the "Four Diagnostic Methods." They are: looking (or observing a patient's complexion and tongue); listening (to a patient's voice and breathing patterns); inquiring (about a patient's physical condition and symptoms); and taking (a patient's pulse). Even today, these four methods remain a foundation for diagnoses in traditional Chinese medicine.

Using his exceptional medical skills, Qin once brought a "dead" man back to life. According to legend, one day he traveled to the state of Guo and saw many people mourning in the streets. Bian Que asked someone what had happened. He was told that a prince of the state, the designated heir to the duke, had just died of no apparent illness.

Bian Que decided to have a look. After introducing himself to the duke, he was taken to see the prince's body. Following careful examination, Bian Que told the duke that the prince was only in a state of "feigned death."

After giving the patient acupuncture and herbal tea, the prince came back to life, and after two more days of treatment had fully recovered.

In addition to Nan Jing, Qin Yueren is also ascribed authorship of "Bian Que's Internal Canon of Medicine" and "Bian Que's External Canon of Medicine." Nowaday, lots of Chinese medical practices are still based on his principles of healing.