In Chinese medicine Jing is the essence of organic life. It refers to the material substance, physical structure and sensate life of a person - the tangible aspects. Jing has two sources: that which a person is born with and that which is created whilst living. The quantity and quality of prenatal Jing (xian-tian-zhi-Jing) is fixed at conception. Together with original Qi, prenatal Jing determines as person's basic makeup and constitution. Postnatal Jing (hou-tian-zhi-Jing) is derived from ingested food. Disharmonies of Jing manifest during development, maturation and reproduction.