Platelets were separated during extracorporeal circulation by the method of Tulliir ct aZ. in the Latham Blood Processor equipped with a 375 ml disposable centrifuge bowl. The average yield of platelets recovered from each 710 ml unit of blood was 0.665 X 1011 2 0.244 X 1011 ( 2 1 S. D.) N =

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Plasmapheresis was performed in normal blood donors using simple plastic equipment. Removal of plasma in amounts up to 1.0 liter at a single venipuncture proved feasible and produced no major changes in the donor’s blood counts and serum protein levels. Chronic plasmapheresis for periods up to 23 weeks with maximal rates not exceeding 1.5 liters of plasma withdrawn per week, produced no changes in formed elements and only minor changes in serum protein levels. Five donors were subjected to acute plasmapheresis with removal of 5 liters of plasma in 5 days. In this group, serum protein depletion was observed with particular depletion appearing at the end of the 5-day period. From calculations of protein replacement, the presence of a ready extravascular protein reserve, of a size somewhat less than the intravascular pool, was suggested. An average maximal protein replacement of 49 Gm. per day was observed during the most intensive plasmapheresis, and the data suggest that protein withdrawals should not exceed this amount if serum protein levels are to be maintained. Although no rebound of serum protein was observed, recovery after depletion required at least 2 to 4 weeks.

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