A system for preparing and making available a flowable medium (43) that is formed by mixing a dry substance (39) with a fluid (41), in particular a medium for therapeutic purposes includes a) a first container (1) receiving the fluid (41) and has a wall part (3) able to deform counter to a restoring force to change the container volume, b) a second container (35) receiving the dry substance (39), and c) a transfer device (21) for producing a fluid communication between the first container (1) and the second container (35).
