1. Rains AJH: Gallstones, Causes and Treatment. London, W. Heineman Medical Books, 1964
2. Miyake H, Johnston CG: Gallstones: Etiological studies. Digestion 1:219?228, 1968
3. Nakayama F: Studies on calculus versus milieu: Gallstone and bile. J Lab Clin Med 77:366?377, 1971
4. Suzuki N: On black pigment of gallstones with special reference to difference from melanins. Tohoku J Exp Med 85:238?247, 1965
5. Koga A, Todo S: Structure study of so-called black gallstones. Nihon Shokakibyo Gakukai Zasshi (Jpn J Gastroenterol) 74:1154?1159, 1977 (in Japanese with English summary)