From the results presented in Part 2 it is supposed that the reticulocyte ripening substances in the bovine liver found by the author may be protein belonging to a globulin fraction or a substance attached to some particles of the cytoplasm, which can not be precipitated by the general centrifugation. The supernatant obtained from the saline extract by centrifuging at a low speed was again put to ultra-centrigu-gation at 40,000 r. p. m., thus splitting fraction into two, soluble fractions and microsome or mitochondrial fractions. Ripening test on reticulocytes proved that the effective substance had been transfered to the soluble fraction. The globulin fraction obtained from the saline exfract by the half saturation with ammonium sulfate also proved to be effective. Electro-paper chromatography of the protein obtained from the saline extract revealed that it contained a fraction of γ-globulin which was found to be lacking in the water extract. Thus the ripening substance of reticulocyte has been prove to be a protein belonging to the γ-globulin fraction originated from the hyaloplasm.