A handheld device for mixing a liquid and a gas to form foam before a treatment procedure comprises: an inlet for letting a liquid enter the device, the inlet adapted for attachment to a syringe containing the liquid, an outlet for letting a formed foam exit the device, a chamber containing a gas, the chamber comprising the inlet and outlet, at least one agitation element disposed in the chamber, the at least one agitation element is arranged for independent movement in at least one degree of freedom, the at least one agitation element sized and shaped to mechanically agitate liquid flowing past the at least one agitation element, the liquid flowing in an overall inlet-to-outlet direction, the agitation being sufficient for the at least some of the liquid to mix with the gas to produce the formed foam; the device is dimensioned for holding in one hand.

A device for restricting flow of a fluid, in particular the flow of water in a sanitary fitting, includes a substantially cylindrical, hollow inlet body for the fluid, and a substantially cylindrical outlet body for the fluid, which is connected to the inlet body so as to be rotatable about a common longitudinal axis, and conducts the fluid via a cross borehole and a following cavity in the direction of the longitudinal axis. A mixing chamber includes a lateral intake borehole from which a further fluid can be supplied from outside the outlet body A clamping device fixes the set radial position of the inlet body and the outlet body relative to each other.