The US as a Net Debtor: The Sustainability of the US External Imbalances

Disclosure is made of an improved assembly for the collection, separation and isolation of serum or plasma from blood without subjecting the desired serum or plasma to contamination by exposure to the atmosphere and which utilizes a thixotropic barrier material to effect the isolation. A representative embodiment of the improved assembly comprises an air-evacuated glass collection container, a self-sealing, airtight elastomeric closure for the container which is penetrable by a blood bearing cannula and a thixotrope having a specific gravity of from about 1.03 to about 1.09 disposed in a specially constructed reservoir positioned adjacent to the closure member and within the air-evacuated collection container.