having applied the picric acid-bromphenol blue ( bpb ) and the phosphomolybdic acid-benzidine ( pma-b ) methods -- the first method detecting the total histone content , the second one only free histones -- we have found that cell nuclei of the rat embryos permanently contain histones , nevertheless , in such a pattern that the free histone appears only at a well-defined stage of embryogenesis .
C0007610
cell nuclei of
C0019652
histone