An improved technique for making thin sections of gallstones has enabled us to examine their morphology microscopically. Using this technique in various types of gallstones, we found a network of mucin, which was considered to play an important role in gallstone formation.

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We used infrared absorption spectroscopy to clarify the characteristics of black pigment in gallstones, which is insoluble and amorphous, and is considered to be a polymer of bilirubin or calcium bilirubinate with tetrapyrrol units. Black stones contain several metallic elemental components that exist as complex compounds with bilirubin. Chemical analysis of gallbladder bile indicates that the mechanism by which unconjugated bilirubin is precipitated depends on the pH level or on bile acid components. Black pigment is formed by the bridging action of mucin, forming complexes with metal ions in the bile. Hemolytic jaundice, liver cirrhosis, and cardiac valve replacement have been implicated in the etiology of black stone formation. In hemolytic jaundice and cardiac valve replacement, overproduction of bilirubin, due to hemolysis, is responsible for black stone formation, while in liver cirrhosis, a high concentration of ionized calcium and increased pH levels are the main factors in such stone formation.eases could be a key to understanding the pathogenesis of black stones. We present recent data on the analysis of black stone composition, and discuss the pathogenesis of black stones based on their composition and the pathophysiology of background diseases. Origin of black pigment Chemical analysis of black stonesOur analysis revealed that an amorphous non-lustrous black residue, insoluble in both water and in organic solvents, constituted 46.6% of the black stones' components, while the amounts of bilirubin and cholesterol, 12.4% and 0.8%, respectively, were much lower than in calcium bilirubinate stones (Table 1). This black residue, the so-called black pigment, which is the main component of black stones, is difficult to analyze by ordinary methods. We used infrared absorption spectroscopy to clarify its characteristics.