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 human 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, ZhangJingyue said: "Man's life relies entirely upon this qi." Classic onMedical Problems states:"qi is ihe root of the human body; once the root is damaged, the stem and leaves would turn withered". And, also, Basic Questions points out : "One's life is the combination of qi of heaven and earth".

    在中医书中，气总是与血和津液相提并论，因为它们都是构成人体和维持生命活动的基本物质。然而，它们之中，气对于人体尤为重要。这就是中医为什么要用气的观点来解释生命活动。因此，张景岳说：“人之有生，全赖此气”。《难经》则指出：“气者，人之根本也；根绝则茎叶枯矣”。《素问》还指出：“天地合气，命之曰人”。

    Qi in the human 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 inhaled from the natural world by the lung. Therefore, qi is a combination of three kinds of factors. It is easy 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.

    人体之气由先天之气和后天之气组成。前者为出生之前秉承父母之气，后者来自与脾胃生化的水谷精微及肺从自然界吸入的清气。因此，气是以上三种因素的结合。很显然气的根源与产生与先天禀赋、后天营养和周围的环境有关，也与肾、脾、胃、肺共同活动有关。

    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 interdependent 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 heads.

    先天之气与后天之气互相补充。先天之气是后天之气产生的物质基础，后天之气则补充和营养先天之气。因此，两者之间是互相依赖的关系—先天之气是后天之气的基础，后天之气营养先天之气。各种气和它们之间的功能极其复杂，不是三言两语可以讲清的。让我们用以下的六个标题来讨论，以提供一个精确的解释。

    1 . Promoting Action of Qi 1.气的推动功能

    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.

    气，一种充满活性的精微物质，对人体的生长发育、脏腑经络的生理活动、血液的产生和循环、津液的产生、散布和排泄都起到促进和推动作用。如果因为气虚而使以上的功能减弱，就会发生以下的病理改变：人体生长发育的停滞、脏腑经络功能减弱、血液凝滞和津液停滞等。

    2. Warming Action of Qi 2.气的温煦功能

    Whether man's body temperature is normal or not depends on the warming action of qi. Classic on Medical Problerns says:" Qi is responsible for warming." Only through the warming action of qi can all zang-fu organs，meridiarns 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 preduces heat, while qi deficiency produces cold."

    人体体温正常与否依赖于气的温煦作用。《难经》曰：气者，温也。只有通过气的温煦作用，脏腑经络和其它组织结构才能行使其正常的功能活动，血液和体液等津液物质才能正常循环。语云：“血得温而运，得寒而凝。 ”例如：阳气不足会导致气的温煦作用减弱，引起恶寒、四肢冰冷、体温降低等等。相反，如气过剩则会导致气无法散热，引起喜冷、发热等症状。《素问》指出：“气实者，热也；气虚者，寒也”。