UROBILIN 495 



The Pigmentation in Icterus. — Living tissues have but a slight 

 tendency to take up bilc-pignicnts, much of the tissue-staining ob- 

 served at autopsy being due to postmortem imbibition from the blood 

 and lymph. Quincke*^® found that after subcutaneous injection of 

 bihrubin only the connective tissue, both cells and intercellular fibrils, 

 becomes diffusely colored; later, it fades out of the cells, leaving only 

 the fibrils stained. Muscle-cells, fat-cells, and vessel-walls take up the 

 pigment only after their death. If the jaundice continues for a long 

 time, the subcutaneous deposits of bilirubin may undergo a slow oxida- 

 tion, the color changing to an olive or to a dirty grayish green. The 

 pigment in the connective tissues is at first in solution, but may be de- 

 posited in a granular form after a considerable amount has accumu- 

 lated. Bile pigments and bile salts may both be present in consider- 

 able amounts in the blood and not pass through the kidneys, and also 

 they may fail to pass into the tissues; hence we may have cholemia 

 without icterus or choluria, because of the firmness with which the pig- 

 ments are bound in the plasma (Hoover^^). 



The question whether in icterus the skin may be colored b}' other 

 pigments than bilirubin, especially by its reduction product, urobilin, 

 seems to have been decided negatively. Bile-pigment is probably not 

 absorbed as such from the intestine in sufficient quantity to cause 

 icterus. Such bile-pigment as enters the blood from the liver is ex- 

 creted through the kidneys chiefly, but also in the sweat. Ordinarily, 

 other secretions (milk, tears, saliva, sputum) are not colored in jaun- 

 dice, but if the secretions are mixed with inflammatory exudations, 

 they may then be colored (e. g., pneumonic sputum). When the bile- 

 pigment is resorbed from the skin, it may be in part transformed into 

 urobilin, which appears in the urine in increased amounts during the 

 period of recovery from jaundice. Part of the bile-pigment is prob- 

 ably eliminated by the liver after the cause of obstruction has been 

 removed from the bile-passages. 



Urobilin" 



This pigment is probably formed chiefly, if not solely, from bile pig- 

 ments by the action of reducing bacteria in the intestine. It is ex- 

 creted in the urine only as its chromogen, urobilinogen, but in the 

 feces both urobilin and urobihnogen may be found; when exposed to 

 air the chromogen oxidizes quickly to urobilin. Addis^* states that 

 bilirubin is reduced to urobilinogen in the bowel and is then largely 

 absorbed, to be at once oxidized and polymerized into urobilin, two 

 molecules of urobilinogen uniting under the influence of oxj^gen to 

 form one of urobilin. In the liver the urobilin is largely worked over 



«« Vichow's Arch., 1884 (95), 125. 



«^ Bibliography and review by Meyer-Betz, Ergeb. inn. Med., 1913 (12), 734; 

 Wilbur and Addis, Arch. Int. Med., 1914 (13), 235. 

 68 Arch. Int. Med., 1915 (15), 412. 



