AN OPERABLE VARIABLE-VOLUME VENTED CONTAINER ASSEMBLY FOR USE IN ADMINISTERING PARENTERAL FLUIDS INCLUDES A HOUSING HAVING A CHAMBER FOR RETAINING FLUID. A DISTAL END PORTION OF THE HOUSING HAS A PASSAGEWAY THERETHROUGH FOR COMMUNICATING WITH THE CHAMBER. VENTING MEANS COMMUNICATING BETWEEN THE CHAMBER THE CHAMBER AND THE EXTERIOR OF THE HOUSING, FOR ALLOWING AIR TO ENTER THE HOUSING AS FLUID LEAVES THE CHAMBER THROUGH THE PASSAGEWAY, IS PROVIDED. THE VENTING MEANS INCLUDES AN AIR-PERMEABLE LIQUID-IMPERMEABLE ELEMENT POSITIONED TO ALLOW GASES PASSING THROUGH THE VENTING MEANS TO PASS THROUGH THE ELEMENT. THE ELEMENT IS POROUS AND CAPABLE OF DEVELOPING SUFFICIENTLY HIGH SURFACE TENSION UNDER CONTACT TO SERVE AS A BARRIER AGAINTS LIQUID PASSAGE THERETHROUGH DURING NORMAL USE OF THE CONTAINER ASSEMBLY. A STOPPER IS SLIDABLY POSITIONED IN FLUID TIGHT ENGAGEMENT INSIDE THE HOUSING.(FIG. 1)
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