Phenylhydrazine injection in salamanders (Triturus sp.) produces a complete loss of all erythrocytes and haemoglobin but does not result in an immediate erythropoietic response. Splenectomized newts survive absence of the erythron most readily. At 11-14 days after injection, the peripheral blood contains numerous, primitive cells which exhibit large, lepto-chromatic nuclei, wide variation in cytoplasmic basophilia, and variation in cell size. These cells constitute a spectrum of cells collectively called ‘erythroid precursor cells’ (EPC) which terminate in the formation of basophilic erythroblasts. Earlier cell forms (at 11 days) contain few cytoplasmic ribosomes and few organelles but the ribosome concentration gradually increases, as does a fibrillogranular precipitate presumed to be associated with haemoglobin synthesis. Metabolically, these cells are engaged in proliferation, RNA, haem, and protein synthesis. Erythroid precursor cells, which comprise 50-60% of the total blood cell population at 11-14 days, are replaced by basophilic erythroblasts at 15-18 days. The morphological and metabolic properties of these cells are compatible with their role in red blood cell formation. However, their similarity to mammalian marrow ‘transitional’ cells and the occurrence of similar cells in association with macrophages suggest possible differentiative potencies along several cell lines. While little is known about the origin of erythroid precursor cells, preliminary experiments suggest that they may be derived from circulating lymphocytes.

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