554 XI. HEMOGLOBIN CATABOLISM, I 



able to find a later publication of this evidence in detail. It is claimed that 

 even fresh bile (sterile?) can transform mesobilane into (/-urobilin. Meso- 

 bilane administered per as or intraduodenally, or incubated with normal 

 feces or with acholic feces plus bile, was found to yield /-tetrahydromesobilene, 

 while acholic feces alone were inactive. The experiments with acholic feces, 

 however, do not appear decisive; Watson assumes that for the conversion 

 of mesobilane into /-tetrahydromesobilane a bile factor and a fecal factor 

 are required. Bacterial reduction is postulated for the reduction of bilirubin 

 to mesobilane, but not for the conversion of mesobilane to (/-urobilin, nor 

 apparently for its conversions to /-tetrahydromesobilane. We have seen 

 above that according to Baumgiirtel, on the contrary, liver enzymes can 

 perform the reduction of bilirubin to mesobilane, but not its further reduc- 

 tion to tetrahydromesobilane; the optical activity of the latter and of (/-uro- 

 bilin indicate bacterial formation. The difference between (/-urobilin and 

 /-tetrahydromesobilene may well be due to the activity of bacteria in the bile 

 which are different from those active in the intestine. 



Formation of mesobilane in the liver. Lemberg and co-workers 

 {171S) found mesobilane as the prevalent urobilinogen in some cases 

 of liver disease, although it usually forms only a small part of the 

 urobilinogen. From this they concluded that mesobilane may be 

 formed by the diseased liver. Baumgartel (i.94) has shown that the 

 liver enzymes can reduce not only biliverdin to bilirubin {cf. above), 

 but also the latter to mesobilane. It is thus likely that the small 

 amount of mesobilane present in normal urobilinogen is formed in 

 this way in the liver. Baumgartel estimates this as 20% of the total 

 urobilinogen, while Lemberg and co-workers {17 IS) found no more 

 than 10%. Further investigations on the conditions which cause an 

 increased formation of mesobilane would be of interest. 



Urobilin in the fetus and newborn. Urobilin is found in the liver and gall 

 bladder of the fetus or the stillborn, and in the urine of the newborn, before 

 bacteria and urobilin are present in the intestine {373,1017,2114,2387,274U 

 3101). This is, however, no proof of extraintestinal formation of urobilin, 

 since Winternitz {3101; cf. also 1273) has shown that urobilin of the mother 

 passes the placenta and is found in the umbilical cord. Urobilin is less 

 readily removed from the circulation of the newborn than from that of the 

 adult. On the other hand, the urobilinuria in icterus neonatorum is explained 

 by Royer {23S7) as due to extraintestinal urobilin formation. 



9.2. Endogenous Urobilin Metabolism 

 9.2.1. Enterohepatic Circulation. While we have seen that there 

 is no convincing evidence for the reab.sorption of bilirubin from the 

 intestine, the enterohepatic circulation of urobilin has been estab- 

 lished beyond doubt. It was first demonstrated by von MUller 



