In TCM books, qi is always mentioned in the same breath with blood and body fluid, for they are all the fundamental substances constituting the hurnan body and maintaining its life activities. However, among them qi is particularly important for the human body. That is why TCM often explains the life activities of the human body in the viewpoint of qi. For this reason, Zhang Jingyue said: "Man's life relies entirely upon this qi." Classic on Medical Problems states: "qi is the root of the human body; once the root is damaged, the sten and leaves would turn withered." And, also, Basic Questions points out : "One's life is the combination of qi of heaven and earth".

Qi in the humạn body is composed of congenital qi and acquired qi. The former is inherited from one's parents before birth,

the latter is derived from cereal essence transformed by the spleen and stomach and fresh air inbaled frorn the natural world by the lung. Therefore, qi is a combination of three kinds of factors. It is casy to see that the source or production of qi is related to innate endowment, acquired nutrition and environmental conditions, and the actions of the kidney, spleen, stomach, lung as well.

Congenital qi and acquired qi complement each other. Congenital qi is the material foundation for the production of acquired

qi, and acquired qi continuously supplements congenital qi with nourishments. Both of them are, therefore, described as an inter-dependent relation-congenital qi promoting acquired qi, which, in turn, nourishing congenital qi. There are all kinds of qi

and, their functions are too intricate to be expounded in a few words. To provide a precise exposition, let's discuss them under six beads.

1. Promoting Action of Qi

Qi, as a sort of refined substance full of vigour, plays a promoting and activating role in the growth and development of the

human body, the physiological activities of the zang-fu organs and meridians, the production and circulation of blood, as well as the production, distribution and excretion of body fluid. If the above functions are weakened due to qi- deficiency, the following pathologic changes will occur: tardy growth and development of the human body, hypofunction of the zang- fu organs and meridians, stagnation of blood, fluid retention, etc.

2. Warming Action of Qi

Whether man's body temperature is normal or not depends on the warming action of qi. Classic on Medical Problems says:"Qi is responsible for warming." Only through the warming action of qi can al zang-fu organs, meridians and other structures

perform their normal functional activities, and can such liquid substances as blood and body fluid circulate normally. As the saying goes: "Blood flows in warmth, while it coagulates in cold." For example, the insufficiency of yang-qi may impair the warming action of qi, causing an aversion to cold, cold limbs. Lowered body temperature and so on. Conversely, qi excess may result in the failure of qi to disperse heat, marked by preference for cold, fever, etc. Basic Questions states, "Qi excess produces heat, while qi deficiency produces cold."

3. Defending Action of Qi

Qi has defending function to defend the body surface against the exogenous pathogens and to combat with the invaded exogenous pathogens to drive them out of the body. The book Basic Questions, therefore, states: "Wben vital qi exists in the body, the exogenous pathogens can not attack the body." And "If the pathogens invade and occupy the body, qi-deficiency is bound to ensue." Thereby leading to illness.

4. Controlling Action of Qi

Qi also has controlling action, by which is meant the ability to control the liquid substances and fix the internal organs in the

body. This is shown in the following aspects:

(1) Keeping the blood flowing within the vessels to prevent it from extravasating without reason.

(2) Controlling and regulating the secretion and excretion of sweat, urine, -sperm, saliva, gastrointestinal juices, etc., to

maintain a relative balance of water metabolism.

(3) Firming the internal organs in their normal positions without prolapse. If this action is impaired, hemorrhage, premature ejaculation, spontaneous sweating, urinary incontinence, and spermatorrhea will occur. If this action fails to work normally,

such prolapses as gastroptosis, nephroptosis, hysteroptosis will be brought about.

The promoting and controlling actions of qi are the two aspects of mutual opposition and mutual complement. Provided

these two actions work harmoniously, blood circulation and water metabolism can be normally carried on.