BLOOD BILIRUBIN

Bilirubin is the most important of the bile pigments, the remaining two, biliverdin and bilicyanin, being oxidation products of bilirubin. It occurs in the blood as an acid and is therefore capable of forming salts differing in properties from the free acid. It is produced as the result of the break-down of the red cells of the blood; this probably occurs in the ramifications of the reticulo-endothelial system and has been shown to be almost entirely extrahepatic. 1 The bilirubin so produced is carried in the blood stream as a colloidal suspension and excreted from the liver into the bile passages. Before this excretion occurs, it undergoes a transformation in the liver cells from the form in which it is found in the blood to that in which it appears in the bile. The exact nature of this conversion is a matter of dispute, but the recent work of Collinson and