Abstract: A syringe for injecting liquids into blood vessels of living bodies comprising a cylinder equipped at one end with an attachment flange and at the other end with a catheter connection. A piston insertable into the cylinder and having a sealing ring arranged in a groove. Between the sealing ring and the inner wall of the cylinder there is arranged a substantially L-shaped slide ring operatively connected with the piston. This slide ring sealing bears by means of a first leg at the inner wall of the cylinder and by means of a second leg in a channel or recess which is parallel to the aforesaid groove. A substantially cylindrical shoulder extending from the channel up to an inclined portion of the tip of the piston extends at least to the center or center line of the deformed sealing ring.