The functions of bile have scarcely been studied in fish, but presumably resemble those in higher vertebrates. In mammals bile is composed mainly of bilirubin and biliverdin, which are breakdown products of haemoglobin, and is produced continuously. These salts act like detergents and serve to emulsify lipids, thus making lipids more accessible to enzymes because of the increased surface area, allowing some lipids to be absorbed undigested as micro-droplets. In mammals, about 80 percent of the bile is recycled through the liver and gall bladder.
5. METHODS OF MEASUREMENT AND ANALYSIS FOR DIGESTION STUDIES