This article is only available in the PDF format. Download the PDF to view the article, as well as its associated figures and tables. IN THE ABSENCE of excessive hemolysis, an increase of bile pigments in the blood or tissues indicates some type of abnormality at the "hepatocellular barrier," i. e., the aggregations of hepatic and reticulo-endothelial elements that separate the blood-containing sinusoids from the bile capillaries. Bilirubin, on which the color of bile depends, is an iron-free derivative of hemoglobin formed by the action of reticulo-endothelial cells at the site of the breakdown of red blood cells that is constantly taking place within the body. In its initial state the pigment "hemobilirubin" or "bilirubinglobin" is firmly conjugated with globin or with an albumin-like constituent of the serum complex. This bilirubinprotein compound is not excreted by the kidney and fails to give a prompt direct color reaction with Ehrlich reagent. It is, however, readily removed from the blood by the liver, so that levels between 0.1 and 1 mg. per hundred cubic centimeters are