Abstract: A pack for slow administration to a patient of extremely accurate volumes of sterile, for example pharmaceutical, nutrient or energy-source liquid, comprises in combination at least three systems adapted to be interconnected. The first system is a flowrate regulator. The second system is, for each sterile liquid administered, a sterile bag with a mobile, flexible and continuous wall which delimits an internal cavity in which is at least one opening enabling it to communicate selectively with the exterior. The third system is a solid or fluid piston operating on the interior or exterior side of the wall of said bag to vary its volume, and, in the case of a fluid piston, at least one alarm means indicating any leak in the wall or one of the walls of the bag, adapted by its existence or its properties to convert non-perceptible leakage into a perceptible phenomenon.