The characteristics of the cerebrospinal fluid in intracranial infections are differentiated according to whether the cause of the intracranial infection is bacterial, viral, fungal, or tuberculosis. 1. If it is viral meningitis, a lumbar puncture is performed to examine the cerebrospinal fluid, which has a clear appearance, mildly elevated protein, and possibly elevated or normal sugar and chloride. 2. The pressure of the cerebrospinal fluid is increased, the protein is also increased, there may be hundreds or thousands of cells, the sugar is very low in the biochemistry, the chloride may also be reduced. 3, if it is tuberculous meningitis, the cerebrospinal fluid may be clear, after a period of resting on the surface of the cerebrospinal fluid can form a film, if biochemical examination, the salt is very low, the sugar may be reduced. If fungus causes intracranial infection, the pressure of lumbar puncture will be very high, which may reach more than 300 mmH2O, and the chloride and sugar may be low, and the protein is high.