A system for preparing an injection includes a first container with a first cavity and a rigid outer wall and two ends, a movable stopper being provided on one side of the first cavity, which sealingly closes this cavity and is displaceable inside the first container and comprising a second container, which encloses a second cavity, one container comprising a first substance, and the other container comprising a second substance. The second container comprises an at least regionally elastic wall and in this way has a variable volume. The second container is designed such that a pressure can be built inside the second container by way of the at least regionally elastic wall. The second container is a tube.
