1. E.D.P. De Robertis, W.W. Nowinski, and F.A. Saez. General Cytology, 3rd Ed., W.B. Saunders Co., Philadelphia, London, p. 60.
2. H. Popper and F. Schaffner. Liver: Structure and Function. The Blakiston Div., McGraw-Hill Book Co.,N.Y., Toronto, London, p.14.