This disclosure relates to a system that comprises means for obtaining a signal representative of the electrocortical activity of the patient, means for analyzing this signal in order to derive from it a signal of depth of anaesthesia, means for monitoring the value and development over time of this signal of depth of anaesthesia, these means being associated with means for calculation of control commands of the injection means, in order to automatically bring the signal of depth of anaesthesia to below a predetermined value during at least one predetermined period of time, in that the means for injection of anaesthetics comprise first means for injection of a hypnotic and second means for injection of a morphinomimetic, in that the means for calculation of the control commands of the injection means comprise means allowing an operator to input a type of induction of anaesthesia chosen from a group of types of induction that differ in terms of the initial concentration of hypnotic, and in that the means for inputting the type of induction comprise means for establishing the initial concentration of hypnotic, which is associated with an initial concentration of morphinomimetic predetermined according to the chosen type of induction.