According to tradition, Jīng is stored in the kidneys and is the most dense physical matter within the body. It is said to be the material basis for the physical body and is yīn in nature, which means it nourishes, fuels, and cools the body. As such it is an important concept in the internal martial arts. Jīng is also believed by some to be the carrier of our heritage. Production of semen, in the man, and menstrual blood, in the woman, are believed to place the biggest strains on jīng. Because of this, some even equate jīng with semen, but this is inaccurate; the jīng circulates through the eight extraordinary vessels and creates marrow and semen, among other functions. Jīng should not be confused with the related concept of jìn, nor with jīng, which appears in many early Chinese book titles, such as the Nèi Jīng, yì jīng and Chá Jīng, the fundamental text on all the knowledge associated with tea. The characteristics which constitute signs of good Jing share the embryological origin of neural crest cells. These cells undergo immense and challenging cellular migrations requiring great organisation. As such, Jing may simply represent the strength of embryological self-organisation in the organism. This will be manifestated most strongly in those cells which require most organisation; that is, the neural crest cells.
Allocation
One is said to be born with a fixed amount of jīng and also can acquire jīng from food and various forms of stimulation Theoretically, jīng is consumed continuously in life; by everyday stress, illness, substance abuse, sexual intemperance, etc. Prenatal jīng is very difficult to be renewed, and it is said it is completely consumed upon dying.
Restoration
Jīng is therefore considered quite important for longevity in traditional Chinese medicine ; many disciplines related to qìgōng are devoted to the replenishment of "lost" jīng by restoration of the post-natal jīng. In particular, the internal martial arts and the Circle Walking of Baguazhang may be used to preserve pre-natal jīng and build post-natal jīng, if performed correctly. Ginseng, particularly Korean and Chinese, is said to bolster the jīng. An early mention of the term in this sense is in a 4th-century BCE chapter called Neiye "Inner Training" of a larger text compiled during the Han dynasty, the Guǎnzi.
