AN INTRAVENOUS CATHETER INTRODUCING DEVICE INCLUDES A BARREL (1), A TUBULAR GRIP MEMBER (21) DISPOSED TO HOLD A NEEDLE SEAT (22) IN A POSITION OF USE SO AS TO PERMIT A TIP END (232) OF A NEEDLE CANNULA (23) TO EXTEND FORWARDLY OF THE BARREL ( 1 ) , A TUBULAR PLUNGER (3) WHICH IS MOVABLE ALONG A PASSAGE (11) OF THE BARREL (1) , AND A TUBULAR RECEPTACLE (34) WHICH IS RETAINED IN AN ACCOMMODATION COMPARTMENT (31) OF THE TUBULAR PLUNGER (3) AND WHICH HAS SOCKET AND AIR-PERMEABLE ENDS (343, 344) AND A FLASHBACK CHAMBER (342) . WHEN THE PLUNGER (3) IS PRESSED FORWARDLY TO PERMIT ENGAGEMENT OF THE SOCKET END (343) WITH A REAR PLUG PORTION (223) OF THE NEEDLE SEAT (22) AND TO RELEASE THE GRIP MEMBER (21) FROM THE BARREL (1) , A REARWARD MOVEMENT OF THE NEEDLE SEAT (22) BY VIRTUE OF A BIASING FORCE OF A BIASING MEMBER (4) WILL FORCE THE RECEPTACLE (34) TO MOVE REARWARDLY SO AS TO RETRACT THE NEEDLE CANNULA (23) INTO THE PASSAGE (11).
