**2. The concept of "Essence" and "Qi"**

"Essence" and "Qi," important categories in the ancient Chinese philosophy, are simple understanding of natural phenomena. The connotation and denotation of the concepts "Essence" and "Qi" are consistent in the ancient Chinese philosophy; both are invisible subtle materials existing in the universe with continuous movement and are the primitive composition of the universe, i.e., "Essence" is "Qi" and is also known as "Essence Qi." The concepts "Essence" and "Qi" in ancient Chinese philosophy were introduced into TCM, great changes about their connotation and denotation have taken place, and "Essence" and "Qi" became two concepts. "Essence" is the overall appellation on tangible materials inherited from the parents and acquired as useful subtle substances to the human body, is the most basic material that constitutes the Zang-Fu, tissues, and organs and maintains life activities of the human body, is the source of human life, and is also the origin of other life materials of the body.

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© 2017 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

© 2016 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, "Qi" in TCM is the overall appellation on all the invisible subtle energetic materials in constant motion in the human body and functional activities of internal organs, is both an important part of the body, and is the power source of vital activities. In terms of its source, Qi originated from Essence and can be converted by Essence and is a more subtle material than Essence; Qi can also produce Essence, Essence, and Qi can be interconverted. In terms of its function, Qi can stimulate and promote the functional activities of the Zang-Fu organs and control the process of the human body; Qi is the fundamental that supports the life activity of the body, so when the movement of Qi stops, the end of life will arrive. Essence belongs to Yin, is tangible, and tends to be a material property; Qi belongs to Yang, is intangible, and tends to be a functional property. Essence is the material basis of viscera functional activities, and Qi is the motive force of promoting and regulating physiological activities of Zang-Fu organs.

Qi, as the master of the brain, regulates Yin-Yang and five elements, tonifies the five vital organs of the human body, keeps the six hollow viscera unobstructed, and is in charge of chemical and biological transformation and defenses. Qi of the human body comes from the congenital Essence inherited from parents, the refined food Essence transformed by the spleen, and the fresh air inhaled by the Lung. After birth, the congenital Essence is stored in the kidney to promote development and to control the reproductive activity of the human body. "Both life and death depend on Qi." Qi always underpins the basic theory of TCM and acts as its cornerstone. Qi has been used as a healing technique in China for 4000 years. This shows that Qi is closely related to health, disease, and life.
