chambers 10 12 entirely when the pistons 16 30 are pushed in completely connected to the second piston 30 is a connecting element 32 designed as a hollow needle for this purpose the piston 30 comprises a suitable for example cylindrical hub 34 fig4 into which the hollow needle 32 may be inserted and retained e g by gluing further a foam producing means 38 is rigidly or loosely and if desired removably connected to the piston 30 which sealingly abuts the inner wall 36 of the gas chamber 12 in particular the foam producing means 38 comprises two sieves 40 that cause the whirling and mixing of the two media and thus the production of foam the foam producing means 38 is connected to the piston 30 through a holder 42 in addition to or instead of two or more sieves the foam producing means 38 may also comprise for example one or more sinter filters impellers coils and or spirals a loose or removable connection between the foam producing means 38 and the piston 30 is advantageous in that the foam producing means 38 can be pulled from the cylindrical hub 38 of the present device together with the syringe 46 when expelling the foam from the syringe 46.