CSF refers to cerebrospinal fluid.1. Normal cerebrospinal fluid exists in the human central nervous system, including the ventricles, subarachnoid space, and central canal of the spinal cord as a colorless, clear fluid that can play a protective, supportive, and nutritional role for the brain and spinal cord. In normal people, the pressure, cell count and biochemical indicators of cerebrospinal fluid have a normal range. 2. If a patient develops central nervous system infection, subarachnoid hemorrhage, meningeal carcinomatosis, or demyelinating disease, the pressure, cell count and biochemical indicators of cerebrospinal fluid, will undergo some changes. For example, in septic meningitis, the pressure of the cerebrospinal fluid is significantly higher than normal, the cell count is significantly higher, the appearance of the cerebrospinal fluid becomes cloudy, like rice soup, not colorless and transparent, the sugar and chloride are reduced, and the protein value is increased. It is possible to determine what disease the patient has by the changes in biochemistry and cell count and pressure. Therefore, cerebrospinal fluid examination, for central nervous system diseases, is a very important adjunctive test.