The changing opinions with respect to the genesis of the bile pigments have recently been reviewed in The Journal.1 From the older conception that bilirubin is formed in the liver cells out of the blood pigment hemoglobin, the pendulum of belief has swung to the conclusion, now supported by highly convincing evidence, that this bile pigment can be generated outside of and independently of the hepatic tissue. Thus, the liver functions primarily, if not exclusively, as an organ of elimination for pigmentary substances, bilirubin and biliverdin, for which there is at present no known function. In the light of current indications, they may consequently be regarded as true excretory substances.
There is another closely related compound, urobilin, which has awakened considerable clinical interest ever since its discovery by Jaffé in 1869. In the urine, a colorless precursor, urobilinogen, or parent substance of this pigment, is frequently present. The chromogen
THE ORIGIN OF UROBILIN. JAMA. 1925;85(7):518. doi:10.1001/jama.1925.02670070038016
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