Because of the work of Mann and his associates, it is now known that the parenchymal cells of the liver serve to excrete bilirubin but not to form it. The demonstration of this fact supplies the key to many riddles. Bilirubin is formed from the pigment of broken-down red blood corpuscles, and is carried in the blood stream to the liver and there excreted. The amount of bilirubin in the blood at any one time serves as a measure both of the destruction of blood and of the function of the liver.
Various methods for determining the quantity of bilirubin in the blood have been devised, but it was not until Davis, working in the Boston City Hospital, published a paper on "The Determination of the Icterus Index with Capillary Blood"1 that a practical method for determining the quantity of bilirubin in the blood of infants and small children
TAYLOR R. THE ICTERUS INDEX IN CHILDREN. Am J Dis Child. 1927;34(6):989-993. doi:10.1001/archpedi.1927.04130240068009