Cerebrospinal fluid: Cerebrospinal fluid is a colorless and transparent liquid existing in ventricles and subarachnoid space. The specific gravity is 1.005, and the total amount is 130 ~ 150ml. The average daily output is 524ml. Cerebrospinal fluid surrounds and supports the whole brain and spinal cord, effectively reducing the weight of the brain to 1/6, and playing a certain protective role in trauma. It plays a role in removing metabolites and inflammatory exudates from lymph in other parts of the body.