UROBILIN AND UROBILINOGEN 165 



Urobilin occurs in normal bile and in normal stool except in that of 

 the new-born. It is present in the urine in negligible quantities. Con- 

 cerning its presence in the blood there is little definite information. If it 

 occurs therein it is not demonstrable by our present methods. The writer 

 has frequently attempted to determine its presence in the serum of patients 

 that were excreting considerable quantities in the urine and stool, but 

 without avail. When normal serum is heated with strong hydrochloric 

 acid a positive Ehrlich reaction is obtained, but this is probably due to 

 decomposition of one of the heterocyclic amino acids, such as tryptophan. 

 Gerhardt and others have obtained the reaction with serous fluids other 

 than blood. Conner and Eoper claim to have found it in the serum of 

 pneumonia patients shortly before death. When urobilin is added to 

 blood it rapidly disappears probably as a result of oxidation by oxyhemo- 

 globin (Roth and Herzfeld). 



An increased amount of urobilin is found in the. stool, in the bile, 

 and occasionally in the urine, in pernicious anemia and other conditions 

 associated with a destruction of red blood cells, and also in diffuse lesions 

 of the liver. Urobilin is absent from the stool in jaundice due to complete 

 closure of the common bile duct and in severe diarrhea. 



Mechanism of Urobilin Formation. The voluminous literature per- 

 taining to this subject abounds in theoretic discussion and hypotheses. 

 The enterogenous theory had its chief exponent in Friederich Mueller (6) 

 (1892). It appears to be least open to criticism, and is supported by 

 numerous clinical and experimental observations. It postulates that uro- 

 bilin results from the reduction of bilirubin by the bacteria of the large 

 intestine. The following evidence is submitted in support of the enterog- 

 enous theory: 1. The transformation of bilirubin into urobilin in vitro 

 by bacteria (Mueller, 1892 (a) ; Fischler (a), 1906). 2. Urobilin is ab- 

 sent from the stool and urine of severely jaundiced patients but. appears 

 when urobilin-free bile is administered by stomach tube (F. Mueller (&), 

 1892). 3. Bilirubin alone is found in the intestine of the new-born until the 

 third day, when urobilin appears coincident with the development of the 

 bacterial flora. 4. Diarrheal stools often contain bilirubin but no urobilin. 

 This is apparently due to the rapid propulsion of the intestinal contents 

 that is, the stool is expelled before the bacteria have had an opportunity 

 to reduce bilirubin. 5. Urobilin is not present in the small intestine where 

 bacteria are absent, but appears distally to the ileocecal valve (Schmidt). 



Normally some urobilin is absorbed from the large intestine and 

 brought to the liver where it is partly excreted into the bile and partly 

 converted into another substance, probably bilirubin. The liver does not 

 permit urobilin to escape into the general circulation. The traces that are 

 normally found in the urine may be due to absorption from the lower 

 bowel by the blood of the inferior hemorrhoidal plexus. 



When extensively diseased the liver may permit urobilin to escape into 



