Supplemented by Kidney Essence, Food Essence produced by the Spleen and Stomach is the main source of Blood. Nutritional values of one's diet and the strengths and weaknesses of Spleen and Stomach can directly influence the formation of Blood. Thanks to the mutual action of the Heart, Lung, Spleen and Liver, Blood continuously circulates around the body within the Vessels. It is carried to the Zang-fu organs as well as to the skin, muscles, tendons and bones. It is through this process that Blood can serve the functions of nourishing and moistening the whole body. Therefore, our normal physiological activities are maintained. Blood is also the material basis of mental activities. To ensure normal circulation of Blood, Vessels must not be obstructed and Blood stasis should not occur. In Chinese medicine, Body Fluids are also known as Jinye. It is subdivided into two kinds. Jin is more dilute, flows easily among the pores, skin and muscles and has a moistening function. Ye has a thicker nature, moving less easily in the joints, viscera, bowels, brain and marrow and has nourishing function. The two Fluids are difficult to separate completely and that is why they are combined into one term, Jinye. Body Fluids are formed from water and food and its distribution and excretion are accomplished by the joint action of many Zang-fu organs, including Spleen, Lung and Kidney. That explains why Chinese medicine always pays much attention to restore the normal functions of the Lung, Spleen and Kidney in the treatment of Jinye Metabolic Disorders. Body Fluids are distributed through the body surface for moistening and nourishing muscles, skin and hair. They moisten and protect the eyes, nose, mouth and ears. They flow into Blood Vessels, turn reddish and transform into Blood. Abnormal retention of Fluids is a pathological process resulting from disturbances of Water Metabolism. This process can lead to the formation of pathological products including Dampness, which are thicker turbid substances, as well as Phlegm, which are even more turbid and thick. Blood and Body Fluids are both liquid substances with a Yin nature. Both Blood and Body Fluids are derived from Food Essence, therefore they have the same source. Severe bleeding can reduce Body Fluids, and similarly, loss of Body Fluids will affect the production of Blood. Qi belongs to Yang and has a warming capacity, while Blood belongs to Yin and carries the nourishing function. Relationships between the two are described in two classical teachings: "Qi is the commander of Blood" and "Blood is the mother of Qi". These concepts are explained as follows. Qi is the motivating force behind Blood formation. Blood can be produced properly only when Qi is prosperous, otherwise, Blood production will be weak. That is why, in clinical practice, Chinese medicine practitioners prefer to treat Blood deficiency with herbs that tonify Qi, together with herbs that nourish Blood. Qi is the driving force which propels Blood to move forward in the Vessels. Blood will flow properly in the body only when Qi is moving smoothly. Stagnation in Qi flow will induce Blood stasis. Blood stasis is a pathological state resulting from a reversed or impaired flow of Blood in the body, or the stagnation of Blood flow in localized body parts. As soon as Blood stasis is formed, it can further affect the circulation of Blood and lead to new pathological changes. This can cause a variety of diseases and syndromes. For instance, if the Heart-qi is deficient, then chest is stressed and shortness of breath may be seen, and Heart Blood stasis may occur. Under such circumstances, Chinese medicine practitioners prefer to prescribe herbs that nourish Qi and remove Blood stasis. Qi has the function of keeping Blood circulating normally within the Vessels and not be leaking out from the Vessels. The function of Qi in bleeding prevention is mainly based on normal function of the Spleen. With reference to the concept of Blood as the mother of Qi, Blood is the provider of nutrients to Qi, facilitating its movement. In this sense, Qi cannot exist wthout Blood. The development as well as transportation of Body Fluids are dependent on Qi sufficiency. The ascending, descending, exiting, and entering of Qi is the driving force for the transportation, distribution, and excretion of Body Fluids as urine and sweat. Meanwhile, Body Fluids are carriers of Qi and therefore, loss of Body Fluids often damages Qi.