Abstract: In the preparation of concentrated fibrinogen extracted from the blood for making fibrin glue for use, e.g., as tissue adhesive or intra-arterial embolizing agent, the blood and subsequently obtained plasma are separated by centrifuging. In order to efficiently and rapidly prepare a small quantity of fibrinogen from a patient's own blood to be administered to the same patient during imminent surgery, an arrangement is disclosed wherein the blood or plasma to be centrifuged is transferred to a flat bag or packet which is then fitted into an insert fixture assembly which reliably secures the packet in the centrifuge cup in a suitable orientation.