ABSTRACT
The primitive erythroblasts in 21 cases of embryonic hearts from 4 to 9 weeks of gestation were studied with a light microscope. The nuclear diameter, the motosis, and the loss of nuclei of the primitive erythoblasts were analyzed quantitatively. The results obtained were as follows. 1. At 4 weeks of gestation, the blood cells consisted of proerythroblasts, along with basophilic polychromatophilic primitive erythroblasts. The nuclear diameter ranged from 3.20 µm to 9.20 µm, but the main range was from 4.20 µm to 6.00 µm. It was revealed that 9.50% had diameter of more than 6 µm. 2. At the fist half of the 7 week gestation when hepatic hemopoiesis developed, the blood cells consisted of basophilic, polychromatophilic, and eosinophilic erythroblasts. Cells of more than 6 µm in nuclear diameter were about 1.10% and thereafter gradually disappeared. The range of the nuclear diameters was from 2.60 µm to 7.00 µm, while a range from 3.40 µm to 5.20 µm wqs the main. The proportion of cells less than 4 µm in nuclear diameter was 39.58% and thereafter rapidly increased. 3. From the second half of 7 weeks to 9 weeks of gestation, the erythrocytes originating from hepatic hemopoiesis increasingly replaced the circulating primitive erythroblasts, which became mature during this time. The erythrocytes showed 72.88% at 9 weeks of gestation. The proportions of cells less than 4 µm in nuclear diameter in the first and second haIves of 8 weeks and 9 weeks were 52.73%, 80.02%, and 89.09%, which represented the rapid destruction of nuclei. 4. Mitosis in the primitive erythroblasts occurred principally up to the early 6th weeks, and very weakly at 8 weeks. 5. As the crown-rump length increased, the average nuclear diameter decreased very significantly (P<0.01, y=-0.2811X + 0.3171). The results suggest that distrilbution of the nuclear diameter, the maturity, the rate of nuclear loss, and the mitotic figure offer credible data for estimating embryonic age.