Studies on bile pigments IV. Direct bilirubin in canine bile

Two forms of the direct bilirubin separated from the dried canine cholecystic bile were subjected to paper chromatography and emission or infra-red spectroscopy, and the following results were obtained: 1. The two forms of the direct bilirubin contain plenty of bile acid or its salt, and benzidine- and ninhydrine-positive substances together with various inorganic elements were also detected. 2. The ester-form bilirubin had carboxyl radical by infrared spectroscopy. But it will not be easily concluded that an existence of carboxyl radical will owe to free carboxyl radical of the dibasic acid bilirubin by the reason why an existence of plenty of bile acid in the sample may inhibit the characteristic absorption of ester. 3. It may be suggested that the two forms of the direct bilirubin combine with bile acid or its salt, and that the affinity between them is stronger in the salt-form bilirubin. 4. It seems probable that properties of the salt-form and ester-form bilirubins are not influenced by an existence of bile acid or its salt, and further by acornbination with it.