Abstract
Summary
(1) Fertilized eggs of the leopard frog, Rana pipiens, were exposed to solutions of radiophosphorus of different activities (65, 300 and 550 microcuries). (2) Auto-radiographs and microphotographs were prepared from whole and sectioned embryos in 7 different stages of development. (3) Auto-radiographs show that the uptake of phosphorus32 is greatest in embryos exposed to the most active solutions and also that the process is a cumulative one, increasing with the age of the embryo. (4) The most active areas of the embryo in each of the stages studied are those areas where cell division is high and the population of cells is largest. (5) With the appearance and differentiation of organ primordia, the rate of phosphorus turnover increases, thus indicating that phosphorus is probably being utilized more rapidly in those areas in the synthesis of nucleoproteins.
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