On Black Pigment of Gallstones with Special Reference to Comparison with Bilirubin Derivatives.

It was found in the preceding experiment that a black pigment isolated from black-appearing gallstones resembled melanins but was definitely different from the latter in the chemical structure. As a continuation of the study, this report depicts the results of comparison of the pigment with black substances prepared in vitro from various bilirubin materials. When synthetic calcium bili rubinate or powdered calcium bilirubinate stone was subjected to heating with hydrochloric acid followed by a certain fractionation procedure, the final products were almost identical with the black pigment in question both in general properties and spectroscopic findings. Free bilirubin also yielded the same product when it was heated with hydrochloric acid in the presence of a small amount of calcium chloride. These facts seem to justify that the black pigment of gallstones is of bilirubin origin. Furthermore, it was revealed that conversion of bilirubin into the black pigment involved a series of polymerizing reactions, the pigment being a high-molecular weight polymer.