Responsiveness of the Erythron to Variations of Oxygen Tension in the Chick Embryo and Young Chicken

The reactivity of the chick embryo erythron to varying ambient oxygen concentrations was investigated. The hemoglobin (Hb) concentration, the hematocrit and red cell count were determined in embryos incubated in 40 % O2, air and 15 % O2. The age of the embryos varied between 9 and 19 days. The results indicated that embryos weighing less than 7 g and approximately less than 14 days old do not increase their Hb, hematocrit or erythrocyte count when exposed to 15 % O2. In embryos aged 16 days or over the 15 % O2 exerts a stimulatory effect: the Hb and hematocrit values exceed those found in the embryos incubated in 40 % O2. The mean corpuscular volume and the mean corpuscular Hb are not affected by differences in ambient oxygen concentrations. It is pointed out that the 15th day of incubation seems to represent a critical phase in chick embryo development—it is not only approximately the date when myeloid erythropoiesis begins to dominate, but also the date when, for instance, some polyamines begin to be synthetized and the hypophysis becomes functionally active.