Today, medical care in China often consists of a mixture of both Western and traditional Chinese medicine although Western-style medicine tends to be dominant. Large public hospitals in cities across the country offer both of these approaches to medical treatment. The Chinese will usually visit a doctor trained in Western medicine if they feel that they are seriously ill and need to be treated quickly. If the problem is not too serious or urgent, the patient will most likely see a traditional doctor who can better restore harmony to the body.    Traditional Chinese medicine, as practiced today and in past centuries, is based upon an array of theories and practices from both foreign and native sources. The history of Chinese medicine is said to go back as far as 5,000 years to the time of Shennong, a divine husbandman credited with the discovery of medicinal herbs.    According to Chinese legend, Shen Nung, the Chinese father of agriculture and leader of an ancient clan, took it upon himself to test, one by one, hundreds of different plants to discover their nutritional and medicinal properties. Many of these turned out to be poisonous to humans. Over the millennia, Chinese have used themselves as guinea pigs in this same way to continue testing plants for their properties of inducing cold(han), heat(jeh), warmth(wen), and coolness(liang). They classified the medicinal effects of the plants on the various parts of the body, then tested them to determine their toxicity, what dosages would be lethal and so forth.     Historical writer Liu Shu reported that " Shennong tasted hundreds of herbs himself; at times, as many as 70 poisonous herbs in one day". The validity of that statement is surely one to be debated but Shennong Bencaojing (Shennong's Classic on material Medical) describes the medicinal effects of some 365 herbs and is the earliest known text of its kind. Another early text, which continues to be a cornerstone in the Chinese medical canon, is Huang Dineijing (The Yellow Emperor's Canon of Interior Medicine). While authorship is unknown, its present-day version is believed to have been compiled between second century BC and eighth century AD and later revised during the Song Dynasty (960 -1279). Over the centuries, volumes upon volumes of commentary have been written about this ancient text. Its influence remains important as the main principles of Chinese medicine are still based on theories first set forth by it.     The stem of Chinese ephedra is a sudorific but its roots, to the contrary, can check perspiration. Cassia bark is warming in nature and is useful in treating colds. Mint is cooling in nature and is used to relieve the symptoms of illness resulting from heat factors. This accumulation of experience strengthened the Chinese understanding of natural phenomena and increased the applications of natural principles in Chinese medicine. The same principles described in the preceding are also applied to assess the patient's living environment, his life rhythms, the foods he prefers or avoids, his personal relationships and his language and gestures as a tool in better understanding his illness and suggesting improvements in various areas. Once the excesses or imbalances are pinpointed, they can be adjusted and physical and mental health and balance restored. This attainment of equilibrium in the body's flow of energy is the ultimate guiding principle of Chinese medical treatment.    Yin-yang philosophy and the theory of five elements form a system of categories that explain the complete relationships between parts of the body and the environment. Yin and yang represent two opposite sides in nature such as hot and cold or light and dark. Each of the different organs is said to have yin or yang characteristics. Balance between the two is vital for maintaining health. The five elements--earth, fire, water, metal and wood-are categories of characteristics into which all known phenomena can be classified. For example, just as water subdues fire, phenomena associated with water are said to control those classified under fire.