Sperm maturation process, the binding to the DNA of the sperm nucleus alkaline protein occurs conversion of the group type, rich in lysine residues of histones have been gradually replaced by rich in arginine and cystine residues of protamine. Under acidic conditions, aniline blue, and the lysine residue is combined to generate a blue or violet blue compound, thereby indicating the existence of the lysine residue protein-rich, and nucleoprotein mature sperm were stained red.