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Medium is a man-made nourishment for the growth and maintenance of microorganisms, plant tissues and animal tissues and generally contains carbohydrates, nitrogenous substances, inorganic salts (including trace elements) and vitamins and water. Different media according to actual needs, add some can not synthesize their own compounds, namely growth factor. Some microorganisms, such as autotrophic microorganisms, do not require a carbon source, so the above substances are only generic. Natural medium also known as complex medium, is containing the chemical composition is not clear or not constant chemical composition of natural organic matter. The natural medium is mainly taken from animal body fluids or isolated from animal tissues. Its advantage is rich in nutrients, good training effect, the disadvantage is the complex composition, the source is limited. There are many types of natural media / fluids, including biological fluids (such as serum), tissue extracts (such as embryonic fluid). Characteristics of natural media and existing problems: Tissue culture technology to establish early, in vitro cultured cells are the use of natural media, such as protein hydrolyzate, serum and so on. Its advantage is rich in nutrients and a variety of cell growth factors, hormones, osmotic pressure, pH and also similar to the body environment, the disadvantage is that it is not a clear mixture of ingredients, subject to its source and regulatory issues, Production process is complex, large differences between batches, and gradually replaced by synthetic medium. In practice, natural media are often used in combination with synthetic media. Currently there are common hydrolyzed milk protein and newborn calf serum. The natural medium in general belongs to the incomplete medium. In practice, natural media are often used in combination with synthetic media. Currently there are common hydrolyzed milk protein and newborn calf serum. Synthetic media are prepared by sequentially adding precisely weighed amounts of high purity chemicals to distilled water and containing the ingredients (including trace elements) as well as their amounts. Synthetic media are generally used for quantitatively demanding studies in the laboratory such as nutrition, metabolism, heredity, identification and bioassays. Reference Manufacture and Application of Microbial Culture Medium Medium Manual Modern Bacteriological Medium and Biochemical Test Manual