THE ROLE OF CELL-FUSION IN ERYTHROPOIESIS .1

The present haemopoietic pathways have been deduced from fixed materia l, and can be criticised on the grounds that they are an interpretatio n of a highly complex cytological picture and open to error. Furthermo re, the pathways have not helped in the search for the haemopoietic st em cell, the initiating and most essential element of the pathways. He nce a different approach to the study of haemopoiesis may be useful, a nd in this regard Sabin's work is valuable. Sabin is one of the few in vestigators who has carried out a study of erythropoiesis on the livin g organism. She studied hanging drop preparations of explanted blastod erms of the chicken, and found that special embryonic cells called ang ioblasts fused to form well demarcated aggregates which were transform ed into erythroblastic islands. In this paper, cell fusion leading to erythropoiesis has been further explored. Leishman stained smears of t he blastoderm of the chicken, the splanchnic mesenchyme of the tadpole , the bone marrow of the juvenile chicken and the bone marrow of the j uvenile frog were studied. Aggregates consisting of a set of nuclei en closed by a common cytoplasm were found in art four tissues, and the o rigin and fate of the aggregates could be deciphered. The aggregates a rose by a fusion of embryonic cells, and after the aggregate had attai ned a certain size, the cytoplasm underwent dissolution, denuding the nuclei. The bare nuclei, by manufacturing a haemoglobinised cytoplasm, were transformed into erythroblasts. The findings not only confirmed Sabin's observations on erythropoiesis in the chicken blastoderm but a lso showed that cell fusion was an integral part of erythropoiesis on a wider scare.