Eight to 25 per cent of intravenously injected Na2Cr51O4 binds firmly with erythrocytes of the chicken, pigeon and duck. Calculation of the maximum life span of these avian red cells was made from the disappearance time of circulating radioactivity. The maximum life span of the chicken erythrocyte was found to be 35 days, of the pigeon erythrocyte 35-45 days, and the duck erythrocyte 42 days. Comparing the life span of avian erythrocytes with those of other animal species, the rate of red cell turnover in the mammals, birds, and reptile (turtle) was found to correlate directly with basal heat production per kilogram body weight.
Using erythrocytes tagged with Na2Cr51O4 in vitro, the total red blood cell volume was found to be 17-24 ml. per Kg. body weight in the rooster, 9-12 ml. per Kg. in the hen, 25-31 ml. per Kg. in the duck, and 31-34 ml. per Kg. in the pigeon. These values proved somewhat lower than those obtained from the indirect estimates of red cell volume, using plasma volume figures and periphera blood hematocrit.