Affections of the central nervous system, including the brain and spinal cord, must necessarily be of a very grave character. Physiologists allow that the brain is chiefly concerned with the mental functions, but, in addition, it also presides over special movements, some of which are voluntary while others are of the excito-motor character. Derangement affecting any important part or nerve centre, either in the form of excess or deficiency of blood, undue pressure, or structural changes, produces either exalted function, or drowsiness going on to stupor, or paralysis.

Disease of the cerebellum or smaller brain causes giddiness and failure of the normal power to regulate the functions of locomotion.

The causes of cerebral derangement are numerous. As the brain presides over many important functions of the body, it is also sympathetically affected when the organs which perform those functions become the seat of structural or functional changes due to accident or disease.

The brain is invested by certain membranes which afford protection on the one hand, and on the other act as a medium through which pass the vessels carrying the necessary supply of blood for the nourishment of its tissues and the exercise of its function.