METHODS

Pure, crystalhe fibrinogen was obtained from the Lister Institute. 250 mg. were dissolved in 10 ml. of sterile distilled water and labelled with radioactive iodine, 13lI, by the method described by Veall, Pearson and Hanley (1955). Between IOO and 200 PC of 1311 were used for tagging the fibrinogen and some 10 per cent of this radioactivity was bound to the protein after completion of the labelling procedure. The solution of labelled fibrinogen was tested for the presence of non-protein bound radioiodme by precipitation of the protein with cold 5 per cent trichloracetic acid and by dialysis for 24 hours against normal saline. Approximately 98 per cent of the radioactivity was bound to the precipitated protein and on two occasions only 4.2 and 6.3 per cent of the total radioactivity passed into the dialyzing saline. A specimen of blood, to serve as a blank for the dextran or Evans blue determinations, was taken from the patient and then a measured quantity of a solution of high molecular weight dextran or Evans blue was injected intravenously, followed immediately afterwards by a known amount of labelled fibrinogen. Ten minutes were allowed to elapse after the completion of the injections and then four venous blood samples were taken into heparinized containers at intervals of approximately 10 minutes. Another four specimens of venous blood were obtained during the next 24 hours and thereafter samples were collected at intervals of I or 2 days for the next 11 to 15 days.