In Vitro Studies of Erythropoiesis I. The Effect of Normal Serum on Heme Synthesis and Oxygen Consumption by Bone 1 1arrow

T HE EVALUATION of the erythropoietic function of the bone marrow in vivo has always beets exceedingly difficult due to the anatomic inaccessibilit.y of the organ and its variable dilution of red cell precursors by fat and other cell types. Its both experimetital aninlals and hunsan beings, studies on erythropoiesis have depended ots itldirect nseasurements of function such as myeloiderythroid ratio, reticulocyte level, fecal urobilitsogen, and, more recently, red cell nsass determinations and serum iron turnover rates. Such in vivo studies have produced nsuch useful information. However, these methods oftets present difficulties when precise measurements are desired, and the observed values are often the result of the itidependent action of several variables. Such difficulties have long made apparent the need for suitable niethods of studying bone marrow activity its vitro. Sitsce the original work of Carrel and Burrows,’ there have been tsumeroits studies of bone marrow by various modifications of the tissue culture technic. The classic method of tissue culture depetsds ots the observation of cells emigrating from pieces of tissue on solid media in the “fihroblast. form.” This method has obvious limitatiotis in the study of the erythroid elements of bone marrow.2 Its recent years most tissue culture studies of bone marrow have followed the cell suspensiotl technic of Osgood atid Browtslee.3 By this nlethod, changes in the total tsumber of cells of various types can be followed duritlg the incubation period. However, in the first 48 hours of culture, accurate evaluation of changes its cell counts is difficult.4 Because of the rapid appearatsce of fibroblasts after two to three days, there is considerable doubt about the viability of eryt.hropoietic elensents its the culture.5 The multiplication of primitive erythroid cells has not heels demonstrated, and the observed process is probably nlaitlly otle of maturatiots. In addition to cell counts, workers in this field have followed chatsges in the morphologic appearance of the bone marrow elemetsts.2 This is subject to the criticism that challges its functional capacity may not be reflected its nsorphologic changes. Its addition, morphologic changes its tissue culture may be produced by other factors, such as changes in pH, inadequate oxygetlation, accutisulatiois of waste products, etc. It is interestiisg to isote that workers studying