Abstract: A measuring instrument for studying fluid samples contains a flexural vibrator. A vibrator tube of which is fixed at at least one clamping position and forms on one side of the clamping position, in particular a carrier unit, a freely projecting vibrator section and on the other side a fluid feed tube section with a feed opening and a fluid discharge tube section with a fluid discharge opening. Accordingly, the vibrator tube is fixed or retained both at its fluid discharge tube section and at its fluid feed tube section with at least one independent holding device provided in addition to the clamping position.