Erythropoietin and the development of erythrocytes. Effect of erythropoietin in vitro which simulates that of a massive dose in vivo.

During the differentiation of erythrocytes some cells develop which contain a high concentration of haemoglobin and no cytoplasmic basophilia. Erythropoietin has the effect of increasing the proportion of these cells in preparations of marrow. Two of the communications which follow discuss the effect on these cells of erythropoietin and of ageing and haemorrhage. The third communication describes a factor in the serum of a polycythaemic calf which enhances the activity of erythropoietin.