An introducer is configured to distinguish an introducer provided with a sheath tube whose wall thickness is reduced, from an introducer provided with a sheath tube whose wall thickness is not reduced, and to recognize the relationship between the inner diameter and the outer diameter for the sheath tube in which the wall thickness is reduced. The device comprises a supply from which the liquid may flow and a receptacle with powder, whereby a drain tube connects the supply with a receiving receptacle which can be held at an inner underpressure. The distl end of the conduit may be substantially opposite the esophagus opening of the patient when the device is inserted into the oropharynx.